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Trazodone is a triazolpyridine derivative approved for the treatment of depression, and currently marketed as oral formulations. The transdermal administration of this drug could reduce side effects, related to peak plasma concentration, and improve patient adherence due to a reduced administration frequency. The aims of this work were: (a) the evaluation of the effect of pH vehicle and permeation enhancers on trazodone permeability across porcine skin ex-vivo; (b) the development and optimization of a transdermal drug delivery system containing trazodone hydrochloride. From the results obtained, it was found that the effect of pH of the vehicle on the permeation of trazodone across the skin is quite complex, because it influences both solubility and partitioning and that the presence of fatty acids in the vehicle has a notable effect on permeation (the enhancement factor obtained was approx. 100). For both the fatty acid selected (oleic and lauric) a parabolic relationship between the transdermal flux and the concentration was found, with an optimum activity in the range 2-3 %. In the second part of the work, different patches were prepared and tested ex-vivo. Overall, the results obtained seem to highlight that drug loading, rather than the components of the adhesive matrix, plays the most relevant role for the permeation of trazodone. The addition of lauric acid, which produced a considerable enhancement in solution, was not effective when included in the patch. The obtained data are promising although probably not clinically relevant for the treatment of depression, but might be interesting for the treatment of insomnia and anxiety disorder, which require much lower doses., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Introduction: Previous studies have examined the correlation between paroxetine concentrations and therapeutic efficacy in patients diagnosed with major depressive disorder (MDD), but findings have been contradictory., Aims: This study aimed to investigate the relationships among plasma concentrations, severity of symptoms, and adverse drug reactions (ADRs) to optimize individual dosing., Methods: Eighty-seven MDD patients, after completing treatment with paroxetine, were divided into low-concentration (LC, n  = 38), medium-concentration (MC, n  = 27), and high-concentration (HC, n  = 22) groups, based on cutoff value concentrations with the 50% response rate and the laboratory alert level from the 2017 consensus guidelines for therapeutic drug monitoring in neuropsychopharmacology. The severity of depression and anxiety was evaluated using a 17-item Hamilton Depression Scale (HAMD-17) and Hamilton Anxiety Scale (HAMA), respectively. Dosage, plasma concentrations, scale scores, and ADRs were recorded across the three groups at different treatment stages to define the therapeutic reference range., Results: The 4-week plasma concentration of paroxetine (65.00 ng/mL) could predict the clinical response in MDD patients at 8 weeks. Symptom relief in patients with 4-week paroxetine concentrations ranging from 65.00 to 120.00 ng/mL at 8 weeks was greater than in those with concentrations below 65.00 ng/mL, with no significant difference observed above this range. In addition, more cases of liver injury and weight gain were observed in patients with high paroxetine concentrations., Conclusion: Our results support that early paroxetine concentration may predict clinical efficacy and the incidence of ADRs, thus improving individual dosing regimens for MDD patients., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: Venlafaxine is frequently prescribed for patients with depression. To control the concentration of venlafaxine within the therapeutic window for the best treatment effect, a model to predict venlafaxine concentration is necessary., Aim: Our objective was to develop a prediction model for venlafaxine concentration using real-world evidence based on machine learning and deep learning techniques., Method: Patients who underwent venlafaxine treatment between November 2019 and August 2022 were included in the study. Important variables affecting venlafaxine concentration were identified using a combination of univariate analysis, sequential forward selection, and machine learning techniques. Predictive performance of nine machine learning and deep learning algorithms were assessed, and the one with the optimal performance was selected for modeling. The final model was interpreted using SHapley Additive exPlanations., Results: A total of 330 eligible patients were included. Five influential variables that affect venlafaxine concentration were venlafaxine daily dose, sex, age, hyperlipidemia, and adenosine deaminase. The venlafaxine concentration prediction model was developed using the eXtreme Gradient Boosting algorithm (R 2  = 0.65, mean absolute error = 77.92, root mean square error = 93.58). In the testing cohort, the accuracy of the predicted concentration within ± 30% of the actual concentration was 73.49%. In the subgroup analysis, the prediction accuracy was 69.39% within the recommended therapeutic range of venlafaxine concentration within ± 30% of the actual value., Conclusion: The XGBoost model for predicting blood concentration of venlafaxine using real-world evidence was developed, guiding the adjustment of regimen in clinical practice., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Background and Objectives: Viloxazine extended-release (viloxazine ER) capsules (Qelbree TM ) is a novel nonstimulant recently approved as a treatment for attention-deficit/hyperactivity disorder in children and adolescents. Here, we determined whether the pharmacokinetics of viloxazine are impacted by consuming the capsule contents sprinkled on applesauce rather than an intact capsule, and the effect of a high-fat meal on the pharmacokinetics of viloxazine ER., Methods: This was a randomized, open-label, crossover, three-treatment, three-period study in healthy adults using orally administered single-dose viloxazine ER 200 mg capsules. Subjects consumed: (1) an intact capsule after a 10-h fast (control condition); (2) the capsule contents sprinkled on one tablespoon of applesauce; and (3) an intact capsule with a standard high-fat meal. Blood samples were collected for 48 h post-dosing. Relative bioavailability analyses were performed to assess the impact of each test condition against the control condition (intact capsule, fasting). The absence of an impact was indicated if the 90% confidence interval (CI) for the least-squares geometric mean ratio (LSGMR) of maximal concentration (C max ), the area under the concentration-time curve from time 0 to the last measurable concentration time (AUC last ), and the area under the concentration-time curve from time 0 to infinity (AUC inf ) were within the predetermined no-difference limits of 80-125%., Results: Out of 27 enrolled subjects, 25 were included in the pharmacokinetic analysis. The LSGMR (90% CI) for viloxazine ER sprinkled vs. intact were 90.10% (83.35-97.40) for C max , 93.71% (89.09-98.57) for AUC last , and 95.37% (89.80-101.28) for AUC inf . The LSGMR (90% CI) for viloxazine ER consumed in the fed state vs. fasting state were 90.86% (84.05-98.21) for C max , 89.68% (85.26-94.33) for AUC last , and 92.35% (86.96-98.07) for AUC inf . The 90% CIs of the LSGMRs were within the predetermined no-difference limits of 80-125%. Viloxazine ER was well tolerated, with most adverse events reported as mild., Conclusions: These data suggest that viloxazine ER can be consumed sprinkled on applesauce or as intact capsules with or without meals without significantly changing its pharmacokinetics., (© 2021. The Author(s).)

Clinical trials of olanzapine combined with fluoxetine (Olanzapine/Fluoxetine Combination, OFC) in the treatment of refractory depression have shown significant efficacy, but the drug-drug interaction (DDI) between them remains unclear. In this report, the pharmacokinetic interaction between olanzapine and fluoxetine was studied in wild-type (WT) and Mdr1a/b gene knockout (KO) rats. By analyzing the pharmacokinetics and tissue distribution of olanzapine in single dose and combination, the potential DDI mediated by P-gp was explored. The results showed that in WT rats, the combination of fluoxetine increased the peak concentration (C max , 44.1 ± 5.1 ng/mL in the combination group vs 9.0 ± 1.5 ng/mL in the monotherapy group) and the exposure (AUC 0-t , 235.8 ± 22.7 h × ng/mL in the combination group vs 47.5 ± 8.4 h × ng/mL in monotherapy group) of olanzapine, and decreased the clearance (CL, 8119.0 ± 677.9 mL/h/kg in the combination group vs 49,469.0 ± 10,306.0 mL/h/kg in monotherapy group). At the same time, fluoxetine significantly increased the in vivo exposure of olanzapine in brain, liver, kidney and ileum of WT rats, indicating the occurrence of DDI. The same phenomenon was observed in Caco-2 cells in vitro as well. However, in KO rats, there was no significant difference in pharmacokinetic parameters between the monotherapy group and the combination group. In conclusion, P-gp plays an important role in the pharmacokinetic interaction between olanzapine and fluoxetine in rats. This study may provide a reference for the clinical safety of olanzapine combined with fluoxetine., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Venlafaxine (VEN) is primarily metabolized by CYP2D6. Although several studies have reported the significant effects of CYP2D6 on VEN and O-desmethylvenlafaxine (ODV) pharmacokinetics in Whites, limited data are available regarding the effects of the Asian-specific CYP2D6 genotype on VEN metabolism. This study evaluated the effects of the CYP2D6*10 and CYP2D6*5 genotypes on the steady-state plasma concentrations of VEN and ODV in Japanese patients., Methods: This study included 75 Japanese patients with depression who were treated with VEN. Steady-state plasma concentrations of VEN and ODV were measured using liquid chromatography. Polymerase chain reaction was used to determine CYP2D6 genotypes. A stepwise multiple regression analysis was performed to analyze the relationship between independent variables (sex, age, smoking habit, and number of mutated alleles, CYP2D6*10 and CYP2D6*5), subject-dependent variables (plasma concentrations of VEN and ODV [all corrected for dose and body weight]), and the ODV/VEN ratio., Results: Significant correlations were observed between the daily dose of VEN (corrected for body weight) and plasma concentrations of VEN (r = 0.498, P < 0.001) and ODV (r = 0.380, P = 0.001); ODV plasma concentrations were approximately 3.2 times higher than VEN plasma concentrations (VEN versus ODV = 18.60 ng/mL versus 59.10 ng/mL). VEN plasma concentrations (corrected for dose and body weight) did not differ with differing numbers of CYP2D6-mutated alleles. However, the ODV/VEN ratio decreased as the number of mutated CYP2D6 alleles increased (P = 0.001)., Conclusions: This is the first study to examine the effects of CYP2D6*10 in a clinical setting. Although no effects on the plasma concentrations of VEN or ODV were observed, CYP2D6 polymorphism affects the ODV/VEN ratio. Further studies are needed to confirm the clinical relevance of these findings., Competing Interests: N. Yasui-Furukori has been a speaker for Otsuka Pharmaceutical Co. Ltd., Mochida Pharmaceutical Co. Ltd., Dainippon Sumitomo Pharmaceutical Co., and MSD Co. K. Shimoda has received research support from Novartis Pharma K.K., Dainippon Sumitomo Pharma Co., Astellas Pharma Inc., Meiji Seika Pharma Co. Ltd., Eisai Co. Ltd., Pfizer Inc., Otsuka Pharmaceutical Co. Ltd., Daiichi Sankyo Co., and Takeda Pharmaceutical Co. Ltd., and honoraria from Eisai Co. Ltd., Mitsubishi Tanabe Pharma Corporation, Takeda Pharmaceutical Co. Ltd., Meiji Seika Pharma Co. Ltd., Janssen Pharmaceutical K.K., Shionogi & Co. Ltd., Dainippon Sumitomo Pharma Co., Daiichi Sankyo Co., and Pfizer Inc. The funders did not have any role in data collection or in the study design, analysis, decision to publish, or preparation of the manuscript. The remaining authors declare no conflict of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

According to previous studies, R-(-)-venlafaxine (VEN) has higher enantioselectivity than S-(+)-VEN, and the plasma concentration of R-(-)-VEN varies depending on CYP2D6 activity. Therefore, we examined the pharmacokinetic effects of CYP2D6*10 genotypes on the steady-state concentrations of the enantiomers of VEN. The individuals were 71 Japanese depressed patients treated with racemic VEN. The concentrations of the enantiomers of VEN and O-desmethylvenlafaxine (ODV) were measured. Polymerase chain reaction (PCR) was used to determine the CYP2D6*10 genotypes. The plasma concentrations of S-(+)-VEN were approximately 1.9-fold higher than those of R-(-)-VEN. The plasma concentrations of S-(+)-VEN and R-(-)-VEN seemed to be higher in individuals with two mutant alleles of CYP2D6*10, although no significant differences were found in the plasma levels of S-(+)-VEN and R-(-)-VEN between CYP2D6*10 genotypes. The number of mutant alleles of CYP2D6*10 was a significant factor associated with the R-(-)-ODV/R-(-)-VEN ratio (P = .004) in multiple regression analysis. This suggests that CYP2D6*10 mutations affect the metabolism of R-(-)-VEN and S-(+)-VEN. Further studies are needed to examine how these findings affect clinical practice., (© 2021 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).)

Venlafaxine (VEN) is a P-glycoprotein (P-gp) substrate, and nifedipine has been described by in vitro and experimental studies as a P-gp inhibitor. The present study aimed to investigate whether nifedipine alters the kinetic disposition of VEN enantiomers and their metabolites in healthy subjects. A crossover study was conducted in 10 healthy subjects phenotyped as extensive metabolizers for cytochrome P450 (CYP) 2D6, CYP2C19, and CYP3A. In phase 1, the subjects received a single oral dose of 150 mg racemic VEN, and in phase 2, a single oral dose of 40 mg nifedipine was administered with the VEN treatment. Plasma concentrations of VEN enantiomers and their metabolites O-desmethylvenlafaxine and N, O- didesmethylvenlafaxine (ODV and DDV, respectively) were evaluated by liquid chromatography with tandem mass spectrometry up to 72 hours after drug administration. Phase 2 was compared with phase 1 using the 90% confidence interval (CI) of the ratio of geometric means for C max and area under the curve (AUC). AUC enantiomeric ratios S-(+)/R-(-) were evaluated within each and between phases using the Wilcoxon test (P ≤ .05). The kinetic disposition of VEN was enantioselective (phase 1) with VEN S-(+)/R-(-) AUC ratio median of 2.83 (AUC 0-∞ , 526 vs 195 ng·h/mL). However, AUC median did not differ between enantiomers for the metabolites ODV (1971 vs 2226 ng·h/mL) and DDV (199 vs 151 ng·h/mL). The 90%CI of the ratio of geometric means showed that the phases are bioequivalent. A single oral dose of 40 mg nifedipine did not alter VEN enantiomer pharmacokinetics in healthy subjects., (© 2020, The American College of Clinical Pharmacology.)

Aim: This paper completes a series of three manuscripts on the clinically relevant evidence of the use of trazodone in major depressive disorder. The first paper provided general clinical guidance on the use of trazodone in major depressive disorder. The second paper evaluated the different clinical scenarios in which trazodone prolonged-release or trazodone Contramid® once-a-day may be more indicated. This third and last paper evaluates the clinically relevant evidence about the use of trazodone in major depressive disorder (MDD) with insomnia., Methods: Medline and Cochrane Library searches were performed using the keywords 'trazodone' AND 'depression' AND 'insomnia', to identify the most relevant literature on the use of trazodone in patients with MDD and insomnia. European and the United States prescribing information was reviewed as well. More weight was given to the information that was deemed as most relevant for daily clinical practice., Results: Trazodone is an effective medication for patients with MDD and insomnia., Discussion: Trazodone is efficacious for the treatment of a broad array of depressive symptoms and is particularly useful for patients presenting with insomnia as one of the symptoms of depression., Conclusions: Trazodone improves sleep and depression and is particularly helpful for patients whose symptoms of depression include insomnia.

The antidepressant bupropion is stereoselectively metabolized and metabolite enantiomers have differential pharmacologic effects, but steady-state enantiomeric disposition is unknown. Controversy persists about bupropion XL 300 mg generic equivalence to brand product, and whether generics might have different stereoselective disposition leading to enantiomeric non-bioequivalence and, thus, clinical nonequivalence. This preplanned follow-on analysis of a prospective, randomized, double-blinded, crossover study of brand and 3 generic bupropion XL 300 mg products measured steady-state enantiomeric plasma and urine parent bupropion and primary and secondary metabolite concentrations and evaluated bioequivalence and pharmacokinetics. Steady-state plasma and urine bupropion disposition was markedly stereoselective, with up to 40-fold differences in plasma concentrations of the active metabolite S,S-hydroxybupropion vs. R,R,-hydroxybupropion. Urine metabolite glucuronides were prominent, but glucuronidation was metabolite-specific and enantioselective. There were no differences between any generic and brand, or between generics, in plasma enantiomer concentrations of bupropion or the major metabolites. All generic products satisfied formal bioequivalence criteria (peak plasma concentration (C max ) and area under the plasma concentration-time curve over 24 hours (AUC 0-24 )) using enantiomers for bupropion as well as for metabolites, and generics were comparable to each other, and were considered bioequivalent, based on enantiomeric analysis. Enantiomeric bioequivalence explains the previously observed therapeutic equivalence of bupropion generics and brand in treating major depression. These results have important implications for understanding the clinical therapeutic effects of bupropion based on complex and stereoselective metabolism., (© 2020 The Authors. Clinical Pharmacology & Therapeutics © 2020 American Society for Clinical Pharmacology and Therapeutics.)

This study evaluated the effect of 3 doses of a trazodone hydrochloride 6% oral drops solution on the QT interval of healthy volunteers. Subjects were randomly assigned to receive a single dose of trazodone 20 mg, 60 mg, and 140 mg, moxifloxacin 400 mg, and trazodone-matched placebo in 5 periods separated by 7-day washouts, according to a double-blind, crossover study design. Subjects were monitored continuously, and triplicate ECGs were extracted from baseline (predose) until 24 hours postdose. Blood samples for trazodone and moxifloxacin analyses were collected at the same time points. The concentration-QTc relationship assessed on placebo-adjusted change from baseline for Fridericia-corrected QT (ΔΔQTcF) was the primary end point. ΔΔQTcF values of 4.5, 12.3, and 19.8 ms for the 20-, 60-, and 140-mg doses were observed at the corresponding trazodone peak plasma concentrations. The upper bound of the 90%CI exceeded 10 ms for the 60- and the 140-mg doses. Time-matched analysis results were in line with these findings. No significant trazodone effect on heart rate or PR or QRS intervals and no clinically significant new morphological changes were present. In this moxifloxacin-validated ECG trial, trazodone had a modest, dose-dependent effect on cardiac repolarization, with no QTc prolongation observed with the 20-mg dose and an effect exceeding the values set in E14 guideline with the 60- and 140-mg doses. The effect on cardiac repolarization is unlikely to represent a clinical risk for ventricular proarrhythmia, but caution should be used with concomitant use of other medications that prolong QT or increase trazodone exposure., (© 2020 The Authors. The Journal of Clinical Pharmacology published by Wiley Periodicals LLC on behalf of American College of Clinical Pharmacology.)

Venlafaxine (VEN), a first-line antidepressant, and Zuojin Pill (ZJP), a common Chinese herbal medicine consisting of Rhizoma Coptidis and Fructus Evodiae , have a high likelihood of combination usage in patients with depression with gastrointestinal complications. ZJP exhibits inhibitory effects on recombinant human cytochrome P450 isoenzymes (rhP450s), especially on CYP2D6, whereas VEN undergoes extensive metabolism by CYP2D6. From this perspective, we investigated the influence of ZJP on the metabolism of VEN in vitro and in rats for the first time. In this study, ZJP significantly inhibited the metabolism of VEN in both rat liver microsomes (RLM) and human liver microsomes (HLM); meanwhile, it inhibited the O -demethylation catalytic activity of RLM, HLM, rhCYP2D6*1/*1, and rhCYP2D6*10/*10, primarily through CYP2D6, with IC 50 values of 129.9, 30.5, 15.4, and 2.3 μg/ml, respectively. Furthermore, the inhibitory effects of ZJP on hepatic metabolism and pharmacokinetics of VEN could also be observed in the pharmacokinetic study of rats. The area under drug concentration-time curve 0 - 24 hour of VEN and its major metabolite O -desmethylvenlafaxine (ODV) increased by 39.6% and 22.8%, respectively. The hepatic exposure of ODV decreased by 57.2% 2 hours after administration ( P = 0.014). In conclusion, ZJP displayed inhibitory effects on hepatic metabolism and pharmacokinetics of VEN in vitro and in rats mainly through inhibition of CYP2D6 activity. The human pharmacokinetic interaction between ZJP and VEN and its associated clinical significance needed to be seriously considered. SIGNIFICANCE STATEMENT: Zuojin Pill, a commonly used Chinese herbal medicine, demonstrates significant inhibitory effects on hepatic metabolism and pharmacokinetics of venlafaxine in vitro and in rats mainly through suppression of CYP2D6 activity. The human pharmacokinetic interaction between Zuojin Pill and venlafaxine and its associated clinical significance needs to be seriously considered., (Copyright © 2020 by The American Society for Pharmacology and Experimental Therapeutics.)

Background: Cancer-related fatigue is a significant problem and is associated with poor quality of life. Behavioral interventions include exercise and cognitive-behavioral therapy, which survivors may be unwilling or unable to adopt. Pharmacologic interventions (e.g., selective serotonin reuptake inhibitors) have been disappointing. One potential therapy is the antidepressant bupropion, a norepinephrine-dopamine reuptake inhibitor that targets both inflammation and the hypothalamic-pituitary-adrenal axis. The current study is intended to provide a rigorous test of the efficacy and tolerability of bupropion for cancer-related fatigue., Methods: A randomized, double-blind, placebo-controlled trial will examine the effects of bupropion on cancer-related fatigue. The trial will be conducted nationwide through the University of Rochester Medical Center (URMC) National Cancer Institute Community Oncology Research Program (NCORP). Disease-free breast cancer survivors (n = 422) who completed chemotherapy and/or radiotherapy 12-60 months previously and report significant fatigue will be randomized 1:1 to receive bupropion (300 mg/day) or placebo. Outcomes will be assessed at baseline and the 12-week follow-up. The primary outcome, fatigue, will be measured with the Functional Assessment of Chronic Illness Therapy - Fatigue (FACIT-F). Secondary outcomes include quality of life, depression, and drug tolerability. Exploratory outcomes include cognition and symptomatology. Potential biological mechanisms and genetic moderators of cancer-related fatigue will also be explored., Discussion: This study is the first placebo-controlled trial to our knowledge to evaluate bupropion for cancer-related fatigue. Positive results could revolutionize the treatment of cancer-related fatigue, as bupropion is safe, inexpensive, widely-available, and may be more tolerable and acceptable for many patients than current, limited treatment options., (Copyright © 2020 Elsevier Inc. All rights reserved.)

There is a paucity of clinical trials for the treatment of pediatric insomnia. This study was designed to predict the doses of trazodone to guide dosing in a clinical trial for pediatric insomnia using physiologically-based pharmacokinetic (PBPK) modeling. Data on the pharmacokinetics of trazodone in children are currently lacking. The interaction potential between trazodone and atomoxetine was also predicted. Doses predicted in the following age groups, with exposures corresponding to adult dosages of 30, 75, and 150 mg once a day (q.d.), respectively, were: (i) 2- to 6-year-old group, doses of 0.35, 0.8, and 1.6 mg/kg q.d.; (ii) >6- to 12-year-old group, doses of 0.4, 1.0, and 1.9 mg/kg q.d.; (iii) >12- to 17-year-old group, doses of 0.4, 1.1, and 2.1 mg/kg q.d. An interaction between trazodone and atomoxetine was predicted to be unlikely. Clinical trials based on the aforementioned predicted dosing are currently in progress, and pharmacokinetic data obtained will enable further refinement of the PBPK models., (© 2019 ANGELINI S.p.A. CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals, Inc. on behalf of the American Society for Clinical Pharmacology and Therapeutics.)

Rat CYP2D1 has been considered as an ortholog of human CYP2D6 To assess the role of CYP2D1 in physiologic processes and drug metabolism, a CYP2D1 -null rat model was generated with a CRISPR/Cas9 method. Seven base pairs were deleted from exon 4 of CYP2D1 of Sprague-Dawley wild-type (WT) rats. The CYP2D1 -null rats were viable and showed no abnormalities in general appearance and behavior. The metabolism of venlafaxine (VLF) was further studied in CYP2D1 -null rats. The V max and intrinsic clearance of the liver microsomes in vitro from CYP2D1 -null rats were decreased (by ∼46% and ∼57% in males and ∼47% and ∼58% in females, respectively), while the Michaelis constant was increased (by ∼24% in males and ∼25% in females) compared with WT rats. In the pharmacokinetic studies, compared with WT rats, VLF in CYP2D1 -null rats had significantly lower apparent total clearance and apparent volume of distribution (decreased by ∼36% and ∼48% in males and ∼23% and ∼25% in females, respectively), significantly increased area under the curve (AUC) from the time of administration to the last time point, AUC from the start of administration to the theoretical extrapolation, and C max (increased by ∼64%, ∼59%, and ∼26% in males and ∼43%, ∼35%, and ∼15% in females, respectively). In addition, O -desmethyl venlafaxine formation was reduced as well in CYP2D1 -null rats compared with that in WT rats. Rat depression models were developed with CYP2D1 -null and WT rats by feeding them separately and exposing them to chronic mild stimulation. VLF showed better efficacy in the WT depression rats compared with that in the CYP2D1 -null rats. In conclusion, a CYP2D1 -null rat model was successfully generated, and CYP2D1 was found to play a certain role in the metabolism and efficacy of venlafaxine. SIGNIFICANCE STATEMENT: A novel CYP2D1 -null rat model was generated using CRISPR/Cas9 technology, and it was found to be a valuable tool in the study of the in vivo function of human CYP2D6. Moreover, our data suggest that the reduced O -desmethyl venlafaxine formation was associated with a lower VLF efficacy in rats., (Copyright © 2019 by The American Society for Pharmacology and Experimental Therapeutics.)

Aims: The aims of this study were to characterize escitalopram pharmacokinetic profile, to identify factors influencing drug exposure, notably drug-drug interactions with antiretrovirals, and to simulate expected exposure under standard dosage regimen., Methods: A population pharmacokinetic analysis was performed using NONMEM. A total of 159 plasma concentration measurements were obtained from 39 human immunodeficiency virus (HIV)-infected and 71 uninfected psychiatric patients. The influence of age, weight, sex, HIV and psychiatric cohorts, racemic citalopram treatment, and comedications on oral clearance was examined. Simulations served to calculate the percentage of patients expected to be under- or over-exposed, considering established therapeutic targets (15-80 ng/mL)., Results: A 1-compartment model with first-order absorption and elimination described the data adequately. The average escitalopram clearance and volume of distribution were 23.1 L/h (interindividual variability 51%), and 920 L, respectively. Escitalopram disposition did not differ between HIV-infected and uninfected patients, and was not affected by antiretroviral treatments. Coadministration of at least 1 proton-pump inhibitor (CYP2C19 inhibitor) modestly influenced escitalopram elimination (clearance decreased by 19%), with limited clinical relevance. Model-based simulations showed that, under a standard regimen of 10 mg once daily, a significant proportion of patients (56%) might be under-exposed., Conclusion: The variability in escitalopram disposition is large and poorly explained by demographic, clinical and environmental covariates, thus suggesting a role for dosage individualization based on therapeutic drug monitoring in case of poor clinical response. Escitalopram disposition is modestly impacted by comedications and therefore no a priori dosage adjustments are needed in patients receiving antiretroviral treatments, including boosted regimens., (© 2019 The British Pharmacological Society.)

Objective: Selective serotonin reuptake inhibitors are commonly used for the treatment of pregnancy-related and postnatal depression. However, only a few studies have evaluated the passage of these drugs into human milk, often with conflicting results. Here, we sought to evaluate the passage of selective serotonin reuptake inhibitors into human milk in the first days after delivery and their potential association with neonatal outcomes. Study design: The passage of selective serotonin reuptake inhibitors into human milk was expressed both as percentage of milk-to-plasma ratio of drug concentrations and as the relative infant dose (RID). Selective serotonin reuptake inhibitors were quantified by high-performance liquid chromatography combined with mass spectrometry. Results: Nineteen women treated with selective serotonin reuptake inhibitors during the third trimester of pregnancy and lactation were considered. Human milk-to-plasma ratios ranged from 51.1% to 703.4%. The patients had a median RID of 1.5%, with differences among the selective serotonin reuptake inhibitors. All newborns had been breastfed from birth up to day three of life. At 1 week follow up, 58% of infants were breastfed, 37% were complementary fed, and 5% were formula fed. No side effects due to passage of selective serotonin reuptake inhibitors into human milk were found. Conclusions: Selective serotonin reuptake inhibitors were detected in human milk, with milk-to-plasma ratios which in some cases exceeded 100%. Given the need for maternal therapy and the low incidence of neonatal adverse events, it is advisable not to preclude breastfeeding a priori but recommend it with careful follow-up.

Bupropion is an atypical antidepressant of the aminoketone group, structurally related to cathinone, associated with a wide interindividual variability. An extensive pharmacokinetic and pharmacodynamic review of bupropion was performed, also focusing on chemical, pharmacological, toxicological, clinical and forensic aspects of this drug without a limiting period. Bupropion is a chiral, basic, highly lipophilic drug, clinically used as racemate that undergoes extensive stereoselective metabolism. Its major active metabolites, hydroxybupropion, threohydrobupropion, and erythrohydrobupropion reach higher plasma concentrations than bupropion. Bupropion exerts its effects mainly by inhibiting dopamine and norepinephrine reuptake and by blocking several nicotinic receptors. Recent reports highlight recreational use of bupropion via intranasal insufflation and intravenous use. Seizures, insomnia, agitation, headache, dry mouth, and nausea are some of the reported adverse effects. Neurologic effects are major signs of intoxication that should be carefully managed. Finally, the characterization of the polymorphic enzymes involved in the metabolism of bupropion is essential to understand factors that may influence the interindividual and intraindividual variability in bupropion metabolite exposure, including the evaluation of potential drug-drug interactions and pharmacogenetic implications.

Objectives: The present paper aimed to assist physicians in the accurate choice among second-generation agents (SGAs) for patients with cardiovascular disease (CVD). Methods: We reviewed the published pharmacokinetic (PK) and pharmacodynamic (PD) clinical data that report potential -or absence of- drug interactions between second-generation agents (SGAs) and CVD drugs most commonly used in cardiology, including antiplatelet drugs and anticoagulants, statins, beta-blockers, angiotensin-converting enzyme inhibitors, calcium channel blockers, diuretics and the antiarrhythmic drugs amiodarone and digoxin. We also reviewed the cardiovascular safety profile that has been published for each class of SGAs and side effects reported by patients with CVD. Results: Most relevant PK/PD data about SGAs and CVD drugs are based on small studies or detailed case reports. In many cases, the drug interactions are at most assessed in healthy volunteers so that the clinical relevance of findings needs further investigation in patients with CVD. Case reports of serious, sometimes fatal reactions due to concomitant administration of certain drugs require careful consideration. The major cardiac side effects of SGAs include HR increase, postural hypotension and slight prolongation of the intraventricular conduction time and QT interval. On normal dosage of antidepressants, both advanced heart block and ventricular arrhythmias could occur in patients with severe heart disease, together with clinically important loss of myocardial contractile force. Conclusions: Data reported in the present review should help physicians about their decision-making processes that govern SGAs use in CVD patients.

Background and Objective: Bupropion is used for the treatment of major depressive disorder. We determined the pharmacokinetics, safety, and tolerability of extended-release bupropion XL in healthy Chinese volunteers., Methods: This open-label, single-center pharmacokinetic study was conducted between May 2016 and June 2016. Eligible volunteers received bupropion XL 150 mg once daily for 5 days, then 300 mg once daily from days 6 to 14. Pharmacokinetic parameters were evaluated after first and repeated doses by non-compartmental and population pharmacokinetic analyses., Results: Fifteen out of 16 enrolled volunteers completed the study. The geometric mean of the bupropion area under the concentration-time curve from 0 to 24 h (AUC 0-24 ) was 498.2 and 1,165.7 h·ng/mL on days 1 and 14, respectively; maximum plasma concentration (C max ) was 49.9 ng/mL on day 1 and steady-state maximum observed plasma concentration (C ss&#95;max ) was 111.9 ng/mL on day 14. Among the three metabolites, hydroxybupropion showed the highest AUC 0-24 and C max . The population pharmacokinetic model findings indicated an apparent oral clearance of 221 L/h for bupropion in a typical healthy 60.9-kg Chinese volunteer., Conclusions: This was the first pharmacokinetic study for bupropion XL and its active metabolites in the Chinese population. The AUC and C max of bupropion XL and its three metabolites increased approximately in a dose-proportional manner with an increase from 150 mg to 300 mg. Adverse events were similar to those reported in studies outside China. A population pharmacokinetic model was developed for bupropion XL, with pharmacokinetics of bupropion adequately described by a two-compartment model with first-order absorption and linear elimination plus lag time., Trial Registration Number: NCT02698553.

Controversy persists about bupropion XL 300 mg generic equivalence to brand product. A prospective, randomized, double-blinded crossover in 70 adults with major depression in stable remission taking any bupropion XL 300 mg tested bioequivalence and therapeutic equivalence of available XL 300 mg products. After a 4-week lead-in on patients' existing bupropion, four 6-week phases evaluated brand and three generics. Patients were uninformed of switching. Drug overencapsulation ensured blinding. There were no differences between any generic and brand, or between generics, in peak plasma concentration (C max ) and area under the plasma concentration-time curve over the 24-hour dosing interval (AUC 0-24 ) for racemic bupropion or major metabolites. All generics met formal bioequivalence criteria for bupropion and metabolites. There were no differences between generics and brand, or between generics, in depression symptoms or side effects, assessed by every 3-week in-person interview and daily smartphone-based self-report. There were no differences in patients' perceptions of bupropion products. Results show three bupropion XL 300 mg generic products are both bioequivalent and not therapeutically different from brand drug and each other., (© 2018 The Authors Clinical Pharmacology & Therapeutics © 2018 American Society for Clinical Pharmacology and Therapeutics.)

Aims: CYP2D6*9, CYP2D6*10 and CYP2D6*41 are the most frequent reduced-function CYP2D6 alleles in Caucasians. Despite lacking in vivo evidence, they are collectively classified with an enzyme activity score of 0.5. Thus, the aim of this study was to compare the functional impact of CYP2D6*9, CYP2D6*10 and CYP2D6*41 on CYP2D6 metabolism in a large patient population., Methods: A total of 1003 patients (mainly Caucasians) with data on CYP2D6 genotype and serum concentrations of venlafaxine and metabolites were included from a therapeutic drug monitoring service in Oslo, Norway. The O-desmethyl-to-N-desmethyl-venlafaxine metabolic ratio (MR) was applied as CYP2D6 biomarker and compared (Mann-Whitney) between carriers of CYP2D6*9-10 (merged) and CYP2D6*41, either combined with CYP2D6*1 or non-coding (null) alleles. MR subgroup estimates were obtained by multiple linear regression for calculations of CYP2D6*9-10 and CYP2D6*41 activity scores., Results: MR was significantly lower in carriers of CYP2D6*41 than CYP2D6*9-10 (P < 0.002). The majority of CYP2D6*41/null carriers (86.7%) had MR in the observed range of CYP2D6null/null carriers compared with the minority of CYP2D6*9-10/null carriers (17.4%). CYP2D6 genotype explained 60.7% of MR variability in the multivariate analysis providing subgroup estimates of 9.54 (95% CI; 7.45-12.20), 3.55 (2.06-6.10), 1.33 (0.87-2.05) and 0.47 (0.35-0.61) in carriers of CYP2D6*1/null (n = 269), CYP2D6*9-10/null (n = 17), CYP2D6*41/null (n = 30) and CYP2D6null/null (n = 95), respectively. Based on these estimates, the calculated activity score of CYP2D6*41 was 0.095 compared to 0.34 for CYP2D6*9-10., Conclusions: CYP2D6 metabolism measured as the O/N-desmethylvenlafaxine ratio is significantly lower in Scandinavian carriers of CYP2D6*41 vs. CYP2D6*9-10. Thus, these alleles should be differentiated when classifying CYP2D6 phenotype from genotype., (© 2018 The British Pharmacological Society.)

1. Bupropion, an antidepressant drug has been approved as a racemate containing equal amounts of R- and S-enantiomers. Recently, the chirality of bupropion has received significant attention in the delineation of stereoselective pharmacokinetic (PK) and disposition data. Although the non-stereoselective metabolism of bupropion was well established, the emerging data suggest that bupropion exhibits complex stereoselective metabolism, leading to the formation of various stereoisomeric metabolites. Along with the chiral PKs of bupropion, hydroxybupropion, threohydrobupropion and erythrohydrobupropion, the metabolism data also provided insights into the roles of both CYP2B6 and CYP2C19 enzymes in the stereoselective disposition. Furthermore, the metabolism studies also suggested specific involvement of CYP2B6 pathway in the stereoselective hydroxylation of bupropion to R,R-hydroxybupropion, which was considered as a better marker for CYP2B6 activity. 2. Other significant learnings were: (1) understanding the in vivo CYP2D6 inhibitory potential of bupropion with respect to the chirality of parent drug and the metabolites; (2) the potential involvement of bupropion and metabolites towards significant down regulation of CYP2D6 mRNA; (3) significant in vivo CYP2D6 inhibitory activity (86%) exhibited by R,R-hydroxybupropion and threohydrobupropion. 3. The newly published data on chiral PKs and disposition of bupropion and its metabolites can be used to gauge the drug-drug interaction potential when bupropion is combined in clinical therapy. Moreover, such data would be useful to understand the consequences (if any), due to the combination of bupropion with other drugs both from a safety and efficacy perspective because of the prevalence of polypharmacy situations in many therapeutic areas including CNS indications.

BACKGROUND AND OBJECTIVE: An increasing trend in prescribing proton pump inhibitors (PPIs) inevitably increases the risk of unwanted drug-drug interactions (DDIs). The aim of this study was to uncover pharmacokinetic interactions between two PPIs-omeprazole and pantoprazole-and venlafaxine., Methods: A therapeutic drug monitoring database contained plasma concentrations of venlafaxine and its active metabolite O-desmethylvenlafaxine. We considered three groups: a group of patients who received venlafaxine without confounding medications (non-PPI group, n = 906); a group of patients who were comedicated with omeprazole (n = 40); and a group of patients comedicated with pantoprazole (n = 40). Plasma concentrations of venlafaxine, O-desmethylvenlafaxine and active moiety (venlafaxine + O-desmethylvenlafaxine), as well as dose-adjusted plasma concentrations, were compared using non-parametrical tests., Results: Daily doses of venlafaxine did not differ between groups (p = 0.949). The Mann-Whitney U test showed significantly higher plasma concentrations of active moiety, as well as venlafaxine and O-desmethylvenlafaxine, in both PPI groups [p = 0.023, p = 0.011, p = 0.026, +29% active moiety, +27% venlafaxine, +36% O-desmethylvenlafaxine (pantoprazole); p = 0.003, p = 0.039 and p < 0.001, +36% active moiety, +27% venlafaxine, +55% O-desmethylvenlafaxine (omeprazole)]. Significantly higher concentration-by-dose (C/D) values for venlafaxine and active moiety were detected in the pantoprazole group (p = 0.013, p = 0.006, respectively), while in the omeprazole group, C/D ratios for all three parameters-venlafaxine, O-desmethylvenlafaxine and active moiety-were significantly higher (p = 0.021, p < 0.001 and p < 0.001, respectively)., Conclusions: Significantly higher plasma concentrations for all parameters (venlafaxine, O-desmethylvenlafaxine, active moiety) suggest clinically relevant inhibitory effects of both PPIs, most likely on the cytochrome P450 (CYP) 2C19-mediated metabolism of venlafaxine. The findings might be the result of different degrees of CYP2C19 involvement, therefore the inhibition of CYP2C19 by both PPIs may lead to an increased metabolism via CYP2D6 to O-desmethylvenlafaxine.

Venlafaxine, a novel third-generation antidepressant drug, has been described as a reference treatment for major depression, owing to its ability of inhibiting both noradrenalin and serotonin neuronal reuptake, and inhibiting dopamine reuptake slightly. However, its clinical application is hampered by a limited brain distribution. Glucosylation is an effective way to enhance the brain targeting ability of drugs, but the bidirectional transport of glucose transporter 1 (GLUT 1 ) might decrease the concentrations of venlafaxine-glucose (V-G) in brain before the release of parent drug venlafaxine. To conquer this drawback of GLUT 1 , "lock-in" thiamine disulfide system (TDS) was introduced to modify the V-G conjugate. Both conjugates could release venlafaxine when incubated with the various buffers, mice plasma, and brain homogenate. The evaluation in vivo demonstrated that venlafaxine-TDS-glucose (V-TDS-G) had an improved targeting ability and significantly increased the level of venlafaxine in brain compared to the naked venlafaxine and V-G. The relative uptake efficiency (RE) and concentration efficiency (CE) were enhanced to 5.69 and 5.70 times higher than that of naked venlafaxine, respectively. The results of this study suggest that the conjugate strategy based on the glucose-TDS (G-TDS) is available to enhance the delivery of central nervous system (CNS) drugs into brain., (© 2017 John Wiley & Sons A/S.)

Background: To uncover pharmacokinetic interactions between venlafaxine and doxepin or mirtazapine in a naturalistic sample., Methods: A therapeutic drug monitoring database containing plasma concentrations of venlafaxine (VEN) and its active metabolite O-desmethylvenlafaxine (ODVEN) was analyzed. We included 1067 of 1594 patients in the analysis. Three study groups were considered; a group of patients under venlafaxine without confounding medications, V 0 (n = 905), a group of patients co-medicated with doxepin, V DOX (n = 25) and a second group, co-medicated with mirtazapine, V MIR , n = 137. Plasma concentrations of VEN, ODVEN and the clinically relevant active moiety, sum of venlafaxine and O-desmethylvenlafaxine (ODVEN) (AM), as well as dose-adjusted plasma concentrations (C/D) were compared., Results: Median concentrations in the doxepin group showed 57.7% and 194.4% higher values for AM and VEN respectively; these differences were statistically significant (p < 0.001 for AM and p = 0.002 for VEN). Similar differences were detected for C/D concentrations of active moiety and VEN (p < 0.001 and p = 0.001) with higher values also in the doxepin group. The ratios ODVEN/VEN were lower in the doxepin group (p < 0.001). A co-medication with mirtazapine did not cause any changes in venlafaxine metabolism., Conclusions: Higher concentrations for VEN and AM imply an inhibiting effect of doxepin on the metabolism of venlafaxine, although the huge variability of concentrations has to be taken into account. It is recommended to monitor plasma concentrations in combination treatment to avoid problems in safety and efficacy., Limitations: Despite the large size of our study sample, the naturalistic nature of this data may arise some concerns of information bias potentially resulting from non-standardized data recording., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Recent preclinical and clinical data suggest that low dose of caffeine enhances the effects of common antidepressants. Here we investigated the effects of chronic administration of caffeine (5mg/kg, twice daily for 14days) and its withdrawal on day 15th on the activity of per se ineffective doses of fluoxetine (5mg/kg) and escitalopram (2mg/kg) given on day 15th. We found decreased immobility time in the forced swim and tail suspension tests in mice in which caffeine was administered simultaneously with antidepressants on day 15th following a 14-day caffeine treatment and no alterations in the spontaneous locomotor activity. A decrease in the level of escitalopram and an increase in the level of caffeine in serum were observed after concomitant administration of these compounds, while the joint administration of caffeine and fluoxetine was not associated with changes in their levels in serum or brain. Caffeine withdrawal caused a decrease in Adora1 mRNA level in the cerebral cortex (Cx). Administration of escitalopram or fluoxetine followed by caffeine withdrawal caused an increase in this gene expression, whereas administration of escitalopram, but not fluoxetine, on day 15th together with caffeine caused a decrease in Adora1 mRNA level in the Cx. Furthermore, antidepressant-like activity observed after joint administration of the tested drugs with caffeine was associated with decreased Slc6a15 mRNA level in the Cx. The results show that withdrawal of caffeine after its chronic intake may change activity of antidepressants with concomitant alterations within monoamine, adenosine and glutamate systems., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: It is well known that the standard doses of a given drug may not have equivalent effects in all patients. To date, the management of depression remains mainly empirical and often poorly evaluated. The development of a personalized medicine in psychiatry may reduce treatment failure, intolerance or resistance, and hence the burden and costs of mood depressive disorders. The Geneva Cocktail Phenotypic approach presents several advantages including the "in vivo" measure of different cytochromes and transporter P-gp activities, their simultaneous determination in a single test, avoiding the influence of variability over time on phenotyping results, the administration of low dose substrates, a limited sampling strategy with an analytical method developed on DBS analysis. The goal of this project is to explore the relationship between the activity of drug-metabolizing enzymes (DME), assessed by a phenotypic approach, and the concentrations of Venlafaxine (VLX) + O-demethyl-venlafaxine (ODV), the efficacy and tolerance of VLX., Methods/design: This study is a multicentre prospective non-randomized open trial. Eligible patients present a major depressive episode, MADRS over or equal to 20, treatment with VLX regardless of the dose during at least 4 weeks. The Phenotype Visit includes VLX and ODV concentration measurement. Following the oral absorption of low doses of omeprazole, midazolam, dextromethorphan, and fexofenadine, drug metabolizing enzymes activity is assessed by specific metabolite/probe concentration ratios from a sample taken 2 h after cocktail administration for CYP2C19, CYP3A4, CYP2D6; and by the determination of the limited area under the curve from the capillary blood samples taken 2-3 and 6 h after cocktail administration for CYP2C19 and P-gp. Two follow-up visits will take place between 25 and 40 days and 50-70 days after inclusion. They include assessment of efficacy, tolerance and observance. Eleven french centres are involved in recruitment, expected to be completed within approximately 2 years with 205 patients. Metabolic ratios are determined in Geneva, Switzerland., Discussion: By showing an association between drug metabolism and VLX concentrations, efficacy and tolerance, there is a hope that testing drug metabolism pathways with a phenotypical approach would help physicians in selecting and dosing antidepressants. The MARVEL study will provide an important contribution to increasing the knowledge of VLX variability and in optimizing the use of methods of personalized therapy in psychiatric settings., Trial Registration: ClinicalTrials.gov NCT02590185 (10/27/2015). This study is currently recruiting participants.

Venlafaxine is a commonly used antidepressant agent. We aimed to provide detailed information on the associations between venlafaxine dose and concentrations of venlafaxine, by patient age and sex. From a therapeutic drug monitoring (TDM) database located at Odense University Hospital, Denmark, we identified all adults for whom the treating physician had requested clinical advice on the TDM result for venlafaxine between 2002 and 2012. We identified 1077 TDM samples of venlafaxine from 334 males and 743 females (median age 45 years), and the median daily dose was 225 mg. Median plasma concentration of venlafaxine and o-desmethylvenlafaxine (ODV) was 306 nmol/L and 861 nmol/L, respectively. The median dose-corrected serum level for venlafaxine was 1.49 nmol/L/mg., while the dose-corrected serum level of men and women were 1.21 nmol/L/mg and 1.60 nmol/L/mg, respectively. The dose-corrected sum of venlafaxine and ODV was 8.91 nmol/L/mg (IQR 6.56-12.26) versus 5.52 nmol/L/mg (IQR 4.16-7.52) for patients above 64 years and below the age of 65 years, respectively. Dose-corrected plasma concentrations of venlafaxine and ODV are increased to a clinically significant degree in patients above the age of 64, and initiation of venlafaxine therapy in the elderly should be made cautiously and supported by drug measurements., (© 2017 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).)

Objectives: Escitalopram (S-CT) is used widely to treat patients with panic disorder (PD) and the CYP2C19 enzyme is responsible for S-CT metabolism. We hypothesized that CYP2C19 polymorphisms were associated with S-CT treatment response in Chinese patients with PD., Patients and Methods: Seventy-eight patients with PD completed the assessment by the Panic Disorder Severity Scale - Chinese Version (PDSS-CV) and the Hamilton Anxiety Scale (HAMA-14) during an 8-week period. All patients were administered a fixed dose of 10 mg/day S-CT. Three CYP2C19 metabolizer phenotypes were analyzed by PCR-genotyping microarray, including extensive metabolizer (EM), intermediate metabolizer, and poor metabolizer (PM)., Results: This prospective, open-label and observational study showed that the proportion of EM (43.6%) was higher than that of PM (10.2%). There were higher response ratios of PDSS-CV in PM (the second to fourth week: 62.5-100%) than in EM (the second to fourth week: 23.5-55.9%) (Ps<0.05); also, there were higher response ratios of HAMA-14 in PM (the second to fourth week: 75.0-100%) than in EM (the second to fourth week: 17.7-52.9%) (Ps<0.05). Treatment response was based on the reduction of PDSS-CV and HAMA compared with the baseline. There was higher reduction of PDSS-CV in the patients with PM (68.78±9.04 for the fourth week and 84.30±9.81 for the eighth week) than EM (49.66±20.77 for the fourth week and 63.12±22.60 for the eighth week) (Ps<0.05); also, there was higher reduction of HAMA-14 in the patients with PM (70.11±8.98 for the fourth week and 81.32±8.25 for the eighth week) than EM (51.51±18.53 for the fourth week and 62.79±18.28 for the eighth week) (Ps<0.05)., Conclusion: The CYP2C19 genetic polymorphism is associated with S-CT treatment response in Chinese patients with PD. CYP2C19 PM could play a key role in early treatment response of S-CT.

Purpose: The prevalence of neuropathic pain is high in the general population, and high priority is given to the management of this pain condition. The treatment of neuropathic pain remains challenging, despite the publication of national and international recommendations. The purpose of this narrative review of venlafaxine (VLX) is to provide a better knowledge of the pharmacology of this drug and a clearer view of its efficacy and tolerability in neuropathic pain., Methods: Two independent reviewers searched PubMed with the following search terms: serotonin and noradrenalin reuptake inhibitors OR VLX hydrochloride AND pain. The reviewers included all clinical studies that investigated VLX in neuropathic pain conditions and excluded animal studies, studies on fibromyalgia, studies that focused on the prevention of neuropathic pain, case reports, and studies that did not clearly describe neuropathic pain in the included patients. We describe the 13 studies that we analyzed., Findings: Eleven were randomized clinical trials, and the comparator was placebo in 8 studies. Nine studies reported that VLX was effective against neuropathic pain. However, among the trials, only one against placebo included a large number of patients with >200 participants and one against prégabaline and carbamazepine had >200 patients. Most of the adverse events reported in the selected studies were consistent with known adverse events of VLX, and most were mild to moderate. However, most studies were of very short duration., Implications: Most of the clinical studies found that VLX was effective and well tolerated. However, given the limited number of study and the limitations of all these studies, further large clinical trials are needed. Currently, considering the limited therapeutic options for treating neuropathic pain and the highly variable nature of responses to all drugs, VLX has a place as a treatment option for neuropathic pain., (Copyright © 2017 Elsevier HS Journals, Inc. All rights reserved.)

What is known and objectives: Multiple adverse drug reactions (ADRs) are expected, and thus should be prevented in the elderly comorbid patient on polypharmacy. Rosuvastatin is commonly prescribed for the treatment and prevention of atherosclerotic diseases, and in rare cases, is associated with rhabdomyolysis. Maprotiline is a tetracyclic antidepressant, infrequently used in the United States, but seemingly more broadly in European countries. Acute colonic pseudo-obstruction (Ogilvie's syndrome) caused by maprotiline has thus far, to our knowledge, not yet been described in the literature., Case Summary: We present a unique case of synchronous rhabdomyolysis and Ogilvie's syndrome in an 80-year-old lung cancer survivor following a recent ischemic stroke for which she was prescribed clopidogrel and rosuvastatin for secondary prevention, and maprotiline for post-stroke, new-onset insomnia and anxiety. The ADRs resolved on removal of the offending agents and initiation of conservative treatment. Retrospective pharmacogenetic testing of the patient's drug-metabolizing enzymes and transporters was performed to guide further management and prevent future potential drug interactions and ADRs. What is novel and conclusions: This is an interesting, albeit unfortunate, complex case that depicts the risk of rare adverse effects to medications and their potential relationship to pharmacogenetics. The impact of anticholinergic side effects of antidepressants on gastrointestinal motility, risk of myopathies with statins, increased susceptibility to ADRs caused by drug-drug interactions, and the utility of pharmacogenomic testing are discussed. The question whether commercially available pharmacogenomic tools are relevant for everyday use to direct patient care and reduce harmful drug-drug interactions is addressed and warrants further research.
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Objectives: To evaluate the pharmacokinetics of paroxetine controlled-release (CR) tablets after single and multiple oral administrations and to evaluate its safety profile in healthy Chinese subjects., Methods: This was a phase 1, open-label, single- and multiple-dose combined study. All 12 healthy subjects received a single oral dose of 25-mg paroxetine CR, followed by a washout period of 5 days. Then, the subjects received multiple oral doses of 25-mg paroxetine CR for 14 consecutive days. Serial venous blood samples were collected 96 hours after single dosing and 24 hours after the last dose in multiple-dosing. Blood samples were analyzed using LC-MS/MS. Pharmacokinetic parameters of paroxetine were calculated via noncompartmental analysis using the WinNonlin software (Pharsight Corp., Mountain View, CA, USA)., Results: For both single- and multiple-dose regimens, a lag time of ~ 4 hours was observed before the absorption of paroxetine CR tablet with a t max of ~ 7 - 9 hours. From single- to multiple-dose regimens, the mean C max increased from 7.08 to 36.95 ng/mL, the mean AUC 0-24h increased from 100.91 to 706.75 h×ng/mL, and the mean t 1/2 increased from 12.3 to 83.6 hours (all p < 0.05). The point estimate and 90% confidence intervals of the C trough ratio indicated that the concentration of paroxetine reached steady state after 14 days of repeated dosing. The point estimate of the accumulation factor indicated that the extent of drug exposure at steady state was ~ 9 times that of single dosing. All reported adverse events were considered to be mild., Conclusions: Paroxetine CR tablet is absorbed with a delay of ~ 4 hours after oral administration, and the accumulation factor is ~ 9 at steady state. Paroxetine CR tablet is well tolerated by healthy Chinese subjects.
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The FDA-approved antidepressant and smoking cessation drug bupropion is known to inhibit dopamine and norepinephrine reuptake transporters, as well as nicotinic acetylcholine receptors (nAChRs) which are cation-conducting members of the Cys-loop superfamily of ion channels, and more broadly pentameric ligand-gated ion channels (pLGICs). In the present study, we examined the ability of bupropion and its primary metabolite hydroxybupropion to block the function of cation-selective serotonin type 3A receptors (5-HT 3A Rs), and further characterized bupropion's pharmacological effects at these receptors. Mouse 5-HT 3A Rs were heterologously expressed in HEK-293 cells or Xenopus laevis oocytes for equilibrium binding studies. In addition, the latter expression system was utilized for functional studies by employing two-electrode voltage-clamp recordings. Both bupropion and hydroxybupropion inhibited serotonin-gated currents from 5-HT 3A Rs reversibly and dose-dependently with inhibitory potencies of 87 μM and 112 μM, respectively. Notably, the measured IC 50 value for hydroxybupropion is within its therapeutically-relevant concentrations. The blockade by bupropion was largely non-competitive and non-use-dependent. Unlike its modulation at cation-selective pLGICs, bupropion displayed no significant inhibition of the function of anion-selective pLGICs. In summary, our results demonstrate allosteric blockade by bupropion of the 5-HT 3A R. Importantly, given the possibility that bupropion's major active metabolite may achieve clinically relevant concentrations in the brain, our novel findings delineate a not yet identified pharmacological principle underlying its antidepressant effect., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The maximum plasma concentration (C max ) and the area under the plasma concentration-time curve (AUC) are commonly used to establish bioequivalence between two formulations of the same oral medication. Similarly, these pharmacokinetic parameters have also been used to establish bioequivalence between two sites of administration for the same injectable formulation. However, these conventional methods of establishing bioequivalence are of limited use when comparing modified-release formulations of a drug, particularly those with rates of absorption that are amenable to change with the site of injection. Inherent differences in the rate of absorption can result in clinically significant differences in early exposure and drug response. Here, we propose the use of the partial AUC (pAUC) as a measure of early exposure to aid in the assessment of bioequivalence between the gluteal and the deltoid site of administration for long-acting injectable antipsychotics.

Serotonin transporter (SERT) inhibitors treat depression by elevating brain extracellular 5-hydroxytryptamine (5-HT Ext ). However, only one-third of patients respond adequately. Treatment-resistant depression (TRD) is a major unmet need. Interestingly, elevating 5-HT Ext beyond what is achieved by a SERT inhibitor appears to treat TRD. Adjunctive administration of 5-hydroxytryptophan (5-HTP) safely elevates 5-HT Ext beyond the SERT inhibitor effect in humans; however, 5-HTP cannot be a clinically viable drug because of its poor pharmacokinetics. A slow-release (SR) delivery mode would be predicted to overcome the pharmacokinetic limitations of 5-HTP, substantially enhancing the pharmacological action and transforming 5-HTP into a clinically viable drug. Animal studies bear out this prediction. Thus, adjunct 5-HTP SR could be an important new treatment for TRD. Here, we review the clinical and preclinical evidence for this treatment., (Copyright © 2016. Published by Elsevier Ltd.)

Bupropion sustained release is used to promote smoking cessation in males and nonpregnant females. However, its efficacy as a smoking cessation aid during pregnancy is not reported. The pregnancy-associated changes in maternal physiology may alter the pharmacokinetics and pharmacodynamics of bupropion and consequently its efficacy in pregnant smokers. Therefore, the aims of this study were to determine the steady-state pharmacokinetics of bupropion during pregnancy and the effect of functional genetic variants of CYP2B6 and CYP2C19 on bupropion pharmacokinetics in pregnant women. Plasma and urine concentrations of bupropion and its metabolites hydroxybupropion (OHBUP), threohydrobupropion, and erythrohydrobupropion were determined by liquid chromatography-mass spectrometry. Subjects were genotyped for five nonsynonymous single-nucleotide polymorphisms that result in seven CYP2B6 alleles, namely *2, *3, *4, *5, *6, *7, and *9, and for CYP2C19 variants *2, *3, and *17 The present study reports that the isoform-specific effect of pregnancy on bupropion-metabolizing enzymes along with the increase of renal elimination of the drug could collectively result in a slight decrease in exposure to bupropion in pregnancy. In contrast, pregnancy-induced increase in CYP2B6-catalyzed bupropion hydroxylation did not impact the plasma levels of OHBUP, probably due to a higher rate of OHBUP glucuronidation, and renal elimination associated with pregnancy. Therefore, exposure to OHBUP, a pharmacologically active metabolite of the bupropion, appears to be similar to that of the nonpregnant state. The predicted metabolic phenotypes of CYP2B6*6 and variant alleles of CYP2C19 in pregnancy are similar to those in the nonpregnant state., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

Bupropion is a widely used antidepressant, smoking cessation aid, and weight-loss therapy. It is administered as a racemic mixture, but the pharmacokinetics and activity of bupropion are stereoselective. The activity and side effects of bupropion are attributed to bupropion and its metabolites S,S- and R,R-OH-bupropion, threohydrobupropion, and erythrohydrobupropion. Yet the stereoselective metabolism in vitro and the enzymes contributing to the stereoselective disposition of bupropion have not been characterized. In humans, the fraction of bupropion metabolized (fm) to the CYP2B6 probe metabolite OH-bupropion is 5-16%, but ticlopidine increases bupropion exposure by 61%, suggesting a 40% CYP2B6 and/or CYP2C19 fm for bupropion. Yet, the CYP2C19 contribution to bupropion clearance has not been defined, and the enzymes contributing to overall bupropion metabolite formation have not been fully characterized. The aim of this study was to characterize the stereoselective metabolism of bupropion in vitro to explain the stereoselective pharmacokinetics and the effect of drug-drug interactions (DDIs) and CYP2C19 pharmacogenetics on bupropion exposure. The data predict that threohydrobupropion accounts for 50 and 82%, OH-bupropion for 34 and 12%, erythrohydrobupropion for 8 and 4%, and 4'-OH-bupropion for 8 and 2% of overall R- and S-bupropion clearance, respectively. The fm,CYP2B6 was predicted to be 21%, and the fm,CYP2C19, 6% for racemic bupropion. Importantly, ticlopidine was found to inhibit all metabolic pathways of bupropion in vitro, including threohydrobupropion, erythrohydrobupropion, and 4'OH-bupropion formation, explaining the in vivo DDI. The stereoselective pharmacokinetics of bupropion were quantitatively explained by the in vitro metabolic clearances and in vivo interconversion between bupropion stereoisomers., (Copyright © 2016 by The Author(s).)

Tryptophan (TRP) is marketed as a calmative for horses despite reservations about its efficacy. The aim of this study was to measure the effect of oral TRP administration on the reaction speed of horses. Sixty mature horses were used in a two stage randomised, blind, cross-over study, receiving a placebo and an oral dose of TRP (30, 60 or 120 mg/kg body weight), before undergoing a reaction speed test. Blood samples were taken up to 96 h after TRP administration, to identify signs of acute haemolytic anaemia. Plasma TRP concentrations were increased (P <0.001) by the administration of TRP paste. However, TRP had no effect on the reaction speed of horses when startled. There was no evidence of alterations in clinical pathology parameters in 432 blood samples. While the safety of these doses of TRP can be confirmed, there was no evidence to suggest that a single dose of TRP is an effective calmative for horses., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Aim: This paper examines the use of Trazodone Contramid® in major depressive disorder (MDD), with a focus on practical guidance regarding real world challenges. The paper includes clinical case reports, developed for didactic reasons, which detail the practical management with Trazodone Contramid® of patients with MDD and either insomnia or anxiety or dementia or isolated (ipo)manic symptoms, which often fulfill the criteria for a diagnosis of MDD with with anxious distress or MDD with mixed features, according to the new DSM-5 classification., Methods: A literature search was performed using appropriate keywords to identify studies where any formulation of trazodone was used. The reference lists of those studies identified were cross-referenced for additional studies., Results: Based on the literature search and our clinical experience, we report that trazodones may be particularly useful in those forms of depression with comorbid anxiety or insomnia or isolated manic symptoms or dementia., Discussion: Trazodone has proven an effective medication in patients with MDD but has not been extensily studied in terms of its efficacy for specific phenotypes of depression. Hereby we report that Trazodone Contramid® may be particularly effective in those forms of MDD that are characterized by comorbid insomnia, and/or anxiety, and/or isolated manic symptoms and/or dementia. These forms of depression are very common and a thorough knowledge of Trazodone Contramid® pharmacological properties will aid choosing and managing this medication at the best., Conclusions: Trazodone contramid is a relatively new formulation of trazodone, which has proven effective in MDD, particularly in those difficult to treat cases of MDD characterized by symptoms such as insomnia, anxiety, dementia or (ipo)manic symptoms. The once-a-day formulation of trazodone may provide a combination of improved tolerability and efficacy over other antidepressants and over the conventional immediate-release formulation of the same medication.

Antidepressants are commonly prescribed medications in the United States, and there is increasing interest in individualizing treatment selection for more than 20 US Food and Drug Administration-approved treatments for major depressive disorder. Providing greater precision to pharmacotherapeutic recommendations for individual patients beyond the large-scale clinical trials evidence base can potentially reduce adverse effect toxicity profiles and increase response rates and overall effectiveness. It is increasingly recognized that genetic variation may contribute to this differential risk to benefit ratio and thus provides a unique opportunity to develop pharmacogenetic guidelines for psychiatry. Key studies and concepts that review the rationale for cytochrome P450 2D6 (CYP2D6) and cytochrome P450 2C19 (CYP2C19) genetic testing can be delineated by serum levels, adverse events, and clinical outcome measures (eg, antidepressant response). In this article, we report the evidence that contributed to the implementation of pharmacokinetic pharmacogenetic guidelines for antidepressants primarily metabolized by CYP2D6 and CYP2C19., (Copyright © 2016 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.)

Psoriasis is a chronic inflammatory disease associated with several comorbidities, including depression. Previous studies have shown that inflammatory diseases downregulate the expression and suppress activity of CYP isoforms. Venlafaxine (VLX) is an antidepressant metabolized mainly by CYP2D6 to O-desmethylvenlafaxine (ODV), CYP3A to N-desmethylvenlafaxine (NDV), and CYP2D6 and CYP3A to N,O-didesmethylvenlafaxine (DDV). This study evaluated the influence of psoriasis on the enantioselective pharmacokinetics of VLX. Psoriasis patients (n = 13) and healthy volunteers (n = 11) phenotyped as CYP2D6 extensive (EM) or poor metabolizers (n = 1) received a single oral dose of 150 mg racemic VLX. Plasma concentrations of TNF-α, IFN-γ, IL-6, IL-8, and IL-17 cytokines were higher in EM psoriasis patients when compared with healthy volunteers. IL-6 plasma concentrations varied from 0.4 to 12.9 pg/mL (mean, 2.1 pg/mL) in healthy volunteers and from 0.4 to 29.3 pg/mL (mean, 4.2 pg/mL) in psoriatic patients. VLX pharmacokinetics are enantioselective in healthy volunteers and psoriasis patients phenotyped as EM. Higher AUC values for the (S)-VLX, (S)-NDV, and (S)-DDV enantiomers were observed in healthy volunteers, whereas higher AUC values for (S)-VLX and (R)-ODV were found in psoriasis patients phenotyped as EM. Psoriasis does not alter the pharmacokinetics of the VLX enantiomers probably because of the low levels of IL-6 plasma concentrations., (© 2015, The American College of Clinical Pharmacology.)

Purpose: To investigate the predictive value of the risperidone and venlafaxine metabolic ratios and CYP2D6 genotype., Methods: The determination of risperidone, 9-hydroxyrisperidone, and venlafaxine, O-desmethylvenlafaxine, N-desmethylvenlafaxine and CYP2D6 genotype was performed in 425 and 491 patients, respectively. The receiver operator characteristic method and the area under the receiver operator characteristic curve were used to illustrate the predictive value of risperidone metabolic ratio for the individual CYP2D6 genotype. To evaluate the proposed cutoff levels of >1 to identify individuals with a poor CYP2D6 genotype, the sensitivity, specificity, positive predictive values, and negative predictive values were calculated., Results: Area under the receiver operator characteristic curve to predict poor metabolizers for risperidone/9-hydroxyrisperidone and N-desmethylvenlafaxine/O-desmethylvenlafaxine ratios was 93% and 99%, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value (confidence interval) of a risperidone/9-hydroxyrisperidone ratio >1 to predict a CYP2D6 poor metabolizer genotype were 91% (76%-97%), 86% (83%-89%), 35% (26%-46%), and 99% (97%-100%), respectively. The corresponding measures for N-desmethylvenlafaxine/O-desmethylvenlafaxine were 93% (76%-97%), 87% (83%-89%), 40% (32%-51%), and 99% (98%-100%)., Conclusions: Risperidone/9-hydroxyrisperidone and N-desmethylvenlafaxine/O-desmethylvenlafaxine metabolic ratios >1 strongly predict individuals with poor metabolizer genotype, which could guide psychotropic drug treatment to avoid adverse drug reactions and to increase their therapeutic efficacy in patients prescribed these drugs.

Paroxetine is a selective serotonin reuptake inhibitor (SSRI) and is used for the treatment of depression and anxiety problems, but suffers from the drawback of poor oral bioavailability (less than 50%) due to its extensive first pass metabolism. The objective of the present study was to develop a paroxetine loaded nanoemulsion (o/w type) for direct nose-to-brain delivery. Nanoemulsions were prepared by the spontaneous emulsification technique using Capmul MCM, Solutol HS 15 and propylene glycol as oil phase, surfactant and co-surfactant, respectively, for delivery of drug directly to the brain through the nasal route for better management of depression. Formulations were studied for droplet size, polydispersity index (PDI), percentage transmittance, refractive index, viscosity, zeta potential, surface morphology and in vitro permeation study. TEM images of optimized formulation showed spherical droplets with a mean diameter of 58.47 ± 3.02 nm, PDI of 0.339 ± 0.007 and zeta potential values of -33 mV. The formulation showed good results for transmittance (100.60 ± 0.577%), refractive index (1.412 ± 0.003) and viscosity (40.85 ± 6.40 cP). Permeation studies revealed a 2.57-fold enhancement in permeation as compared to the paroxetine suspension. Behavioural studies such as the forced swimming test and locomotor activity test were done on Wistar rats to study the antidepressant effect of the optimized formulation. Treatment of depressed rats with paroxetine nanoemulsion (administered intranasally) significantly improved the behavioural activities in comparison to paroxetine suspension (orally administered). Biochemical estimation results revealed that the prepared nanoemulsion was effective in enhancing the depressed levels of glutathione and decreasing the elevated levels of TBARS.

Background/aims: The study aimed at investigating the effects of multiple-dose bupropion (potent inhibitor of CYP2D6) on the pharmacokinetics (PKs) of single-dose nebivolol (CYP2D6 substrate) and to evaluate the clinical relevance of this potential drug interaction., Methods: This open-label, nonrandomized clinical study had a 2-period design: during period 1 (reference), a single dose of 5 mg nebivolol was administered, while during period 2 (test), 5 mg nebivolol + 300 mg bupropion were ingested concomitantly, after a pretreatment regimen with bupropion (7 days). The PK parameters of nebivolol and its active metabolite were analyzed by noncompartmental modeling, while the pharmacodynamic (PD) parameters (blood pressure and heart rate) were assessed at rest., Results: Bupropion plus nebivolol increased the mean peak plasma concentrations (Cmax) of nebivolol (1.67 ± 0.69 vs. 3.80 ± 1.70 ng/ml) and its active metabolite (0.68 ± 0.22 vs. 1.13 ± 0.38 ng/ml) compared to nebivolol alone. After bupropion pretreatment, the exposure to nebivolol was increased by 7.2-fold for the parent drug and 4-fold for the hydroxylated active metabolite. The difference between the PD parameters measured during the 2 periods was not significant., Conclusion: The study concluded that bupropion influenced the PKs of nebivolol in healthy volunteers, but a clinical relevance was not established. However, this latter aspect requires further investigation., (© 2016 S. Karger AG, Basel.)

Introduction: Second-generation antipsychotics (SGAs) are frequently co-prescribed with drug metabolic inducers and inhibitors. SGA pharmacokinetic drug-drug interactions (DDIs) with inducers and inhibitors have not received enough attention in the literature but can be studied in by using therapeutic drug monitoring (TDM)., Areas Covered: The limited information available on oral SGA pharmacokinetic DDIs is reviewed. A systematic literature search on the available oral SGA TDM studies is completed. By integrating TDM studies with the information on in vitro metabolism studies, case report/series and prospective studies, a table is provided to manage average SGA patients taking inducers or inhibitors by using TDM and/or dose SGA changes. Adding an inhibitor or discontinuing an inducer may increase plasma concentrations and cause adverse drug reactions (ADRs) on clozapine or risperidone. Quetiapine and lurasidone, which are very sensitive to decreases of plasma concentrations by induction, should not be administered with potent inducers. Prescribing sertindole with TDM may make its use safer., Expert Opinion: Reading our article may encourage: 1) clinicians using these combinations to publish TDM case reports/series to demonstrate whether our dose indications are correct or not, in their patients with DDIs; and 2) pharmacokinetic researchers to study these DDIs in prospective and retrospective ways using large TDM databases.

Bupropion hydrochloride is a norepinephrine-dopamine disinhibitor (NDDI) approved for the treatment of depression and smoking cessation. Bupropion is a trimethylated monocyclic phenylaminoketone second-generation antidepressant, which differs structurally from most antidepressants, and resides in a novel mechanistic class that has no direct action on the serotonin system. Comprehensive chemical, physical, and spectroscopic profiles are presented. This analytical profile provides an extensive spectroscopic investigation utilizing mass spectrometry, one- and two-dimensional NMR, solid-state NMR, IR, NIR, Raman, UV, and X-ray diffraction. The profile also includes significant wet chemistry studies for pH, solubility, solution, and plasma stability. Both HPLC and UPLC methodology are presented for bupropion and its related impurities or major metabolites. The profile concludes with an overview of biological properties that includes toxicity, drug metabolism, and pharmacokinetics., (© 2016 Elsevier Inc. All rights reserved.)

Chimeric mice with humanized livers (PXB mice) are used to investigate the metabolism and pharmacokinetics of drugs in humans. However, residual murine enzymatic activities derived from the liver and the presence of mouse small intestinal metabolism can hamper the prediction of human drug metabolism. Recently murine Cytochrome P450 3a gene knockout chimeric mice with humanized livers (Cyp3a KO CM) were developed. To evaluate the prediction of drug metabolism, nefazodone (NEF) was administered orally at 10 mg/kg to the following mouse strains: Cyp3a KO CM, murine Cyp3a gene knockout (Cyp3a KO), PXB and severe combined immunodeficiency (SCID) mice. Liquid chromatography-mass spectrometry was used for metabolic profiling of plasma, urine and bile. The prediction of human metabolite levels such as hydroxy nefazodone (OH-NEF), triazoledione form (TD), m-chlorophenylpiperazine and dealkyl metabolites in Cyp3a KO CM was superior to that in Cyp3a KO, PXB or SCID mice. Further, clinical exposure levels of NEF, OH-NEF and TD were reproduced in Cyp3a KO CM. In contrast, NEF was rapidly metabolized to TD in both PXB and SCID mice but not in Cyp3a KO mice, suggesting that murine CYP3A is involved in the elimination of NEF in these mice. These findings demonstrate that the metabolic profile of NEF in Cyp3a KO CM differs qualitatively and quantitatively from that in PXB mice due to the higher metabolic rate of NEF and its metabolites via murine CYP3A. Therefore Cyp3a KO CM might be useful in predicting the metabolic profiles of drug candidates in humans., (Copyright © 2016 John Wiley & Sons, Ltd.)

A population PK model was developed in order to simultaneously describe citalopram and its major metabolite, n-desmethyl citalopram, plasma concentrations in two different strain of rats after intravenous (IV) and oral (PO) administration of citalopram. Citalopram was administered to Sprague-Dawley (SD) rats at doses: 0.3, 1, 3, and 10 mg/kg IV and 10 mg/kg PO. The compound was dosed orally to Wistar rats at doses: 0.3, 1, 3, 10, 30 and 60 mg/kg. Plasma samples were collected for citalopram and metabolite. Pharmacokinetic analyses were conducted using NONMEM 7.2. Values below the quantification limit (BLQ < 0.1 ng/mL) were included in the analyses and treated as censored information. The disposition of citalopram was best described by a 3-compartment model and its desmethyl metabolite by a 2-compartment model. Several models for the absorption rate were explored (e.g. first, zero order and combined first and zero order absorption, Michaelis-Menten, lag time) in combination with dose and/or time dependent covariate effects. Dose dependent oral bioavailability properties were also identified in this analysis. Citalopram IV clearance and metabolite formation rate were adequately described as linear processes. Metabolite clearance was adequately described using a Michaelis-Menten clearance with different parameters depending on the strain. This analysis demonstrates a very complex absorption/metabolism process explaining the highly non-linear pharmacokinetics observed across all the doses. This is the first combined parent/metabolite population PK analysis in both SD and Wistar rats over a wide range of IV and PO dosages for citalopram, a compound that exhibits highly nonlinear oral pharmacokinetics in rats.