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Mechanisms by which efavirenz diminishes methadone plasma concentrations are unknown. This investigation determined efavirenz influence on clinical methadone disposition and miosis, intravenous and oral alfentanil clearance (hepatic and intestinal cytochrome P450 3A4/5 (CYP3A4/5) activity), fexofenadine disposition (intestinal transporters activity), and efavirenz clearance and 8-hydroxylation (CYP2B6 activity), and human hepatocyte effects. Efavirenz induced systemic and oral alfentanil clearances two- to fivefold and induced efavirenz 8-hydroxylation. Efavirenz stereoselectively decreased methadone plasma concentrations 50-70%. Methadone systemic and oral clearances, hepatic clearance and extraction ratio, N-demethylation, and metabolite formation clearance were stereoselectively increased two- to threefold. Bioavailability decreased. Efavirenz shifted methadone concentration-miosis curves leftward and upward. Efavirenz induced hepatocyte CYP2B6 and CYP3A4 expression, activity, and methadone N-demethylation. Results show that efavirenz coinduced hepatic CYP2B6 and CYP3A4/5, coinduced hepatic and intestinal CYP3A4/5, and coinduced gastrointestinal CYP3A4/5 and efflux transporters. Methadone disposition was most consistent with efavirenz induction of hepatic CYP2B6-mediated methadone N-demethylation. Efavirenz may alter methadone pharmacodynamics. [ABSTRACT FROM AUTHOR]

Ritonavir diminishes methadone plasma concentrations, an effect attributed to CYP3A induction, but the actual mechanisms are unknown. We determined short-term (2-day) and steady-state (2-week) ritonavir effects on intestinal and hepatic CYP3A4/5 (probed with intravenous (IV) and oral alfentanil (ALF) and with miosis) and P-glycoprotein (P-gp) (fexofenadine), and on methadone pharmacokinetics and pharmacodynamics in healthy volunteers. Acute ritonavir increased the area under the concentration-time curve (AUC)0–∞/dose ratio (ritonavir/control) for oral ALF 25-fold. Steady-state ritonavir increased the AUC0–∞/dose ratio for IV and oral ALF 4- and 10-fold, respectively; reduced hepatic extraction (from 0.26 to 0.07) and intestinal extraction (from 0.51 to 0); and increased bioavailability (from 37 to 95%). Acute ritonavir inhibits first-pass CYP3A >96%. Chronic ritonavir inhibits hepatic CYP3A (>70%) and first-pass CYP3A (>90%). Acute and steady-state ritonavir increased the fexofenadine AUC0–∞ 2.8- and 1.4-fold, respectively, suggesting P-gp inhibition. Steady-state compared with acute ritonavir caused mild apparent induction of P-gp and hepatic CYP3A, but net inhibition still predominated. Ritonavir inhibited both intestinal and hepatic CYP3A and drug transport. ALF miosis noninvasively determined CYP3A inhibition by ritonavir.Clinical Pharmacology & Therapeutics (2008); 84, 4, 506–512 doi:10.1038/clpt.2008.102 [ABSTRACT FROM AUTHOR]

Ritonavir diminishes methadone plasma concentrations, an effect attributed to CYP3A induction, but the actual mechanisms are unknown. We determined ritonavir effects on stereoselective methadone pharmacokinetics and clinical effects (pupillary miosis) in healthy human immunodeficiency virus–negative volunteers. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone after no ritonavir, short-term (3-day) ritonavir, and steady-state ritonavir. Acute and steady-state ritonavir, respectively, caused 1.5- and 2-fold induction of systemic and apparent oral R- and S-methadone clearances. Ritonavir increased renal clearance 40–50%, and stereoselectively (S > R) increased hepatic methadone N-demethylation 50–80%, extraction twofold, and clearance twofold. Bioavailability was unchanged despite significant inhibition of intestinal P-glycoprotein. Intestinal and hepatic CYP3A was inhibited >70%. Ritonavir shifted methadone plasma concentration-miosis curves leftward and upward. Rapid ritonavir induction of methadone clearance results from increased renal clearance and induced hepatic metabolism. Induction of methadone metabolism occurred despite profound CYP3A inhibition, suggesting no role for CYP3A in clinical methadone metabolism and clearance. Ritonavir may alter methadone pharmacodynamics.Clinical Pharmacology & Therapeutics (2008); 84, 4, 497–505 doi:10.1038/clpt.2008.104 [ABSTRACT FROM AUTHOR]

Fostemsavir is an approved gp120‐directed attachment inhibitor and prodrug for the treatment of human immunodeficiency virus type 1 infection in combination with other antiretrovirals (ARVs) in heavily treatment‐experienced adults with multi‐drug resistance, intolerance, or safety concerns with their current ARV regimen. Initial in vitro studies indicated that temsavir, the active moiety of fostemsavir, and its metabolites, inhibited organic cation transporter (OCT)1, OCT2, and multidrug and toxin extrusion transporters (MATEs) at tested concentration of 100 uM, although risk assessment based on the current Food and Drug Administration in vitro drug–drug interaction (DDI) guidance using the mechanistic static model did not reveal any clinically relevant inhibition on OCTs and MATEs. However, a DDI risk was flagged with EMA static model predictions. Hence, a physiologically based pharmacokinetic (PBPK) model of fostemsavir/temsavir was developed to further assess the DDI risk potential of OCT and MATEs inhibition by temsavir and predict changes in metformin (a sensitive OCT and MATEs substrate) exposure. No clinically relevant impact on metformin concentrations across a wide range of temsavir concentrations was predicted; therefore, no dose adjustment is recommended for metformin when co‐administered with fostemsavir. [ABSTRACT FROM AUTHOR]

Intestinal P‐glycoprotein (P‐gp) activity plays a crucial role in modulating the oral bioavailability of its substrates. Fexofenadine has commonly been used as a P‐gp probe, although it is important to note the involvement of other drug transporters like, OATP1B1, OATP1B3, and OATP2B1. In vitro studies demonstrated an upregulation of P‐gp protein in response to exposure to pregnancy‐related hormones. The objective of this study was to investigate how intestinal P‐gp activity is impacted by menopausal status. This study sampled fexofenadine plasma concentrations over 0–12 h after probe drug administration from two groups of patients with breast cancer: premenopausal (n = 20) and postmenopausal (n = 20). Fexofenadine plasma concentrations were quantified using liquid‐chromatography tandem mass spectrometry. Area under the plasma concentration‐time curve from zero to infinity (AUCinf) was calculated through limited sampling strategies equation. Multiple linear regression was applied on AUCinf, maximum plasma concentration (Cmax), and time to Cmax. Postmenopausal patients showed a significant increase in Cmax (geometric mean and 95% confidence interval [CI] 143.54, 110.95–176.13 vs. 223.54 ng/mL, 161.02–286.06 and in AUCinf 685.55, 534.98–878.50 vs. 933.54 ng·h/mL 735.45–1184.99) compared to premenopausal patients. The carriers of the ABCB1 3435 allele T displayed higher Cmax values of 166.59 (95% CI: 129.44–214.39) compared to the wild type at 147.47 ng/mL (95% CI: 111.91–194.34, p = 0.02). In postmenopausal individuals, the decrease in P‐gp activity of ~40% may lead to an increased plasma exposure of orally administered P‐gp substrates. [ABSTRACT FROM AUTHOR]

The author discusses drug interactions with methadone, which have resulted in methadone-associated respiratory depression, and prolongation of the electrocardiographic QT interval. The author says that the current product label for oral methadone was updated in October 2006, and information provided therein is not accurate, and the product label needs to be revised. The author says that studies are unable to establish CYP3A as the predominant enzyme in methadone clearance.

Cardiovascular disease (CVD) is the leading cause of death worldwide. Physical activity interventions improve almost all modifiable CVD risk factors, but the effect of physical activity on low density lipoprotein cholesterol (LDL‐C) is uncertain. This may be due to lack of research on the feeding status in which the physical activity is performed. The aim of this study is to investigate the effect of fasted versus fed exercise on LDL‐C concentrations in males and females. One hundred healthy participants, equal males and females, aged between 25 and 60 years will be recruited and will undergo a home‐based 12‐week exercise intervention. After baseline testing, participants will be randomized to a fasted exercise (exercise after an 8‐h fast) or fed exercise (exercise 90–180 min after ingestion of 1 g kg−1 CHO) group and will perform 50 min of moderate intensity exercise (e.g., 95% heart rate of lactate threshold 1) three times a week either before or after a high carbohydrate (1 g kg−1) meal. Participants will visit the laboratory again at week 4 and week 12 and measurements will be taken for body composition, resting blood pressure, fasting blood glucose, lipid profiles and systemic inflammation, lactate threshold, and 14‐day blood glucose control. [ABSTRACT FROM AUTHOR]

Aims: Methadone metabolism and clearance are determined principally by polymorphic cytochrome P4502B6 (CYP2B6). Some CYP2B6 allelic variants affect methadone metabolism in vitro and disposition in vivo. We assessed methadone metabolism by CYP2B6 minor variants in vitro. We also assessed the influence of CYP2B6 variants, and P450 oxidoreductase (POR) and CYP2C19 variants, on methadone clearance in surgical patients in vivo. Methods: CYP2B6 and P450 oxidoreductase variants were coexpressed with cytochrome b5. The metabolism of methadone racemate and enantiomers was measured at therapeutic concentrations and intrinsic clearances were determined. Adolescents receiving methadone for surgery were genotyped for CYP2B6, CYP2C19 and POR, and methadone clearance and metabolite formation clearance were determined. Results: In vitro, CYP2B6.4 was more active than wild‐type CYP2B6.1. CYPs 2B6.5, 2B6.6, 2B6.7, 2B6.9, 2B6.17, 2B6.19 and 2B6.26 were less active. CYPs 2B6.16 and 2B6.18 were inactive. CYP2B6.1 expressed with POR variants POR.28, POR.5 and P228L had lower rates of methadone metabolism than wild‐type reductase. In vivo, methadone clinical clearance decreased linearly with the number of CYP2B6 slow metabolizer alleles, but was not different in CYP2C19 slow or rapid metabolizer phenotypes, or in carriers of the POR*28 allele. Conclusions: Several CYP2B6 and POR variants were slow metabolizers of methadone in vitro. Polymorphisms in CYP2B6, but not CYP2C19 or P450 reductase, affected methadone clearance in vivo. CYP2B6 polymorphisms 516G>T and 983T>C code for canonical loss of function variants and should be assessed when considering genetic influences on clinical methadone disposition. These complementary translational in vitro and in vivo results inform on pharmacogenetic variability affecting methadone disposition in patients. [ABSTRACT FROM AUTHOR]

Although rifampin drug–drug interaction (DDI) studies are routinely conducted, there have been instances of liver function test (LFT) elevations, warranting further evaluation. A literature review was conducted to identify studies in which combination with rifampin resulted in hepatic events and evaluate any similarities. Over 600 abstracts and manuscripts describing rifampin DDI studies were first evaluated, of which 30 clinical studies reported LFT elevations. Out of these, 11 studies included ritonavir in combination with other drug(s) in the rifampin DDI study. The number of subjects that were discontinued from treatment on these studies ranged from 0 to 71 (0–100% of subjects in each study). The number of subjects hospitalized for adverse events in these studies ranged from 0 to 41 (0–83.67% of subjects in each study). LFT elevations in greater than 50% of subjects were noted during the concomitant administration of rifampin with ritonavir‐boosted protease inhibitors and with lorlatinib; with labeled contraindication due to observed hepatotoxicity related safety findings only for saquinavir/ritonavir and lorlatinib. In the lorlatinib and ritonavir DDI studies, considerable LFT elevations were observed rapidly, typically within 24–72 h following co‐administration. A possible sequence effect has been speculated, where rifampin induction prior to administration of the combination may be associated with increased severity of the LFT elevations. The potential role of rifampin in the metabolic activation of certain drugs into metabolites with hepatic effects needs to be taken into consideration when conducting rifampin DDI studies, particularly those for which the metabolic profiles are not fully elucidated. [ABSTRACT FROM AUTHOR]

Obesity is an increasingly alarming public health threat, with nearly 20% of children classified as obese in the United States today. Children with obesity are commonly prescribed the opioids fentanyl and methadone, and accurate dosing is critical to reducing the risk of serious adverse events associated with overexposure. However, pharmacokinetic studies in children with obesity are challenging to conduct, so there is limited information to guide fentanyl and methadone dosing in these children. To address this clinical knowledge gap, physiologically‐based pharmacokinetic models of fentanyl and methadone were developed in adults and scaled to children with and without obesity to explore the interplay of obesity, age, and pharmacogenomics. These models included key obesity‐induced changes in physiology and pharmacogenomic effects. Model predictions captured observed concentrations in children with obesity well, with an overall average fold error of 0.72 and 1.08 for fentanyl and methadone, respectively. Model simulations support a reduced fentanyl dose (1 vs. 2 μg/kg/h) starting at an earlier age (6 years) in virtual children with obesity, highlighting the importance of considering both age and obesity status when selecting an infusion rate most likely to achieve steady‐state concentrations within the target range. Methadone dosing simulations highlight the importance of considering genotype in addition to obesity status when possible, as cytochrome P450 (CYP)2B6*6/*6 virtual children with obesity required half the dose to match the exposure of wildtype children without obesity. This physiologically‐based pharmacokinetic modeling approach can be applied to explore dosing of other critical drugs in children with obesity. [ABSTRACT FROM AUTHOR]

Background: Although aortic stenosis (AS) is the most common valvular heart disease in the western world, many affected patients remain undiagnosed. Auscultation is a readily available screening tool for AS. However, it requires a high level of professional expertise. Hypothesis: An AI algorithm can detect AS using audio files with the same accuracy as experienced cardiologists. Methods: A deep neural network (DNN) was trained by preprocessed audio files of 100 patients with AS and 100 controls. The DNN's performance was evaluated with a test data set of 40 patients. The primary outcome measures were sensitivity, specificity, and F1‐score. Results of the DNN were compared with the performance of cardiologists, residents, and medical students. Results: Eighteen percent of patients without AS and 22% of patients with AS showed an additional moderate or severe mitral regurgitation. The DNN showed a sensitivity of 0.90 (0.81–0.99), a specificity of 1, and an F1‐score of 0.95 (0.89–1.0) for the detection of AS. In comparison, we calculated an F1‐score of 0.94 (0.86–1.0) for cardiologists, 0.88 (0.78–0.98) for residents, and 0.88 (0.78–0.98) for students. Conclusions: The present study shows that deep learning‐guided auscultation predicts significant AS with similar accuracy as cardiologists. The results of this pilot study suggest that AI‐assisted auscultation may help general practitioners without special cardiology training in daily practice. [ABSTRACT FROM AUTHOR]

Background and Purpose: P‐glycoprotein (P‐gp) exhibits a broad substrate specificity and affects pharmacokinetics, especially intestinal absorption. However, prediction, in vivo, of P‐gp‐mediated drug–drug interaction (DDI) and non‐linear absorption at the preclinical stage, is challenging. Here we evaluate the use of human MDR1 mouse artificial chromosome (hMDR1‐MAC) mice carrying human P‐gp and lacking their own murine P‐gp to quantitatively predict human P‐gp‐mediated DDI and non‐linear absorption. Experimental Approach The P‐gp substrates (aliskiren, betrixaban, celiprolol, digoxin, fexofenadine and talinolol) were administered orally to wild‐type, Mdr1a/b‐knockout (KO) and hMDR1‐MAC mice, and their plasma concentrations were measured. We calculated the ratio of area under the curve (AUCR) in mice (AUCMdr1a/b‐KO/AUCwild‐type or AUCMdr1a/b‐KO/AUChMDR1‐MAC) estimated as attributable to complete P‐gp inhibition and the human AUCR with and without P‐gp inhibitor administration. The correlations of AUCRhuman with AUCRwild‐type and AUCRhMDR1‐MAC were investigated. For aliskiren, betrixaban and celiprolol, the Km and Vmax values for P‐gp in hMDR1‐MAC mice and humans were optimized from different dosing studies using GastroPlus. The correlations of Km and Vmax for P‐gp between human and hMDR1‐MAC mice were investigated. Key Results: A better correlation between AUCRhuman and AUCRhMDR1‐MAC (R2 = 0.88) was observed. Moreover, good relationships of Km (R2 = 1.00) and Vmax (R2 = 0.98) for P‐gp between humans and hMDR1‐MAC mice were observed. Conclusions and Implications: These results suggest that P‐gp‐mediated DDI and non‐linear absorption can be predicted using hMDR1‐MAC mice. These mice are a useful in vivo tool for quantitatively predicting P‐gp‐mediated disposition in drug discovery and development. [ABSTRACT FROM AUTHOR]

Direct oral anticoagulants, such as apixaban and rivaroxaban, are important for the treatment and prophylaxis of venous thromboembolism and to reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation. Because apixaban and rivaroxaban are predominantly eliminated by cytochrome P450 (CYP) 3A and P‐glycoprotein (P‐gp), concomitant use of combined P‐gp and strong CYP3A4 inhibitors and inducers should be avoided. Physiologically‐based pharmacokinetic models for apixaban and rivaroxaban were developed to estimate the net effect of CYP3A induction, P‐gp inhibition, and P‐gp induction by rifampicin. The disposition of rivaroxaban is more complex compared with apixaban because both hepatic and renal P‐gp is considered to contribute to rivaroxaban elimination. Furthermore, organic anion transporter‐3, a renal uptake transporter, may also contribute the elimination of rivaroxaban from systemic circulation. The models were verified with observed clinical drug–drug interactions with CYP3A and P‐gp inhibitors. With the developed models, the predicted area under the concentration time curve and maximum concentration ratios were 0.43 and 0.48, respectively, for apixaban, and 0.50–0.52 and 0.72–0.73, respectively, for rivaroxaban when coadministered with 600 mg multiple doses of rifampicin and that were very close to observed data. The impact of each of the elimination pathways was assessed for rivaroxaban, and inhibition of CYP3A led to a larger impact over intestinal and hepatic P‐gp. Inhibition of renal organic anion transporter‐3 or P‐gp led to an overall modest interaction. The developed apixaban and rivaroxaban models can be further applied to the investigation of interactions with other P‐gp and/or CYP3A4 inhibitors and inducers. [ABSTRACT FROM AUTHOR]

The evaluation of potential of a new molecular entity (NME) to inhibit P‐glycoprotein (P‐gp) in vivo is an integral part of drug development and is recommended by regulatory agencies. In this study, we compared the performance of 5 prediction methods and their associated criteria (including those from the European Medicines Agency, the US Food and Drug Administration, and the Pharmaceuticals and Medical Devices Agency of Japan) for assessing the potential of an NME to inhibit P‐gp in vivo based on in vitro assessment. We collected in vitro (eg, half‐maximal inhibitory concentration [IC50], fraction unbound to plasma protein) and in vivo (eg, dose, maximum concentration, change in maximum concentration or area under the plasma concentration–time curve of the substrate digoxin) data for 50 Food and Drug Administration–approved, orally administered drug products containing 53 NMEs, from the University of Washington Metabolism and Transport Drug Interaction Database, Drugs@FDA, and PubMed. All methods yielded similar accuracy with small differences in false‐negative (FN) and false‐positive (FP) predictions. In addition, use of ratio of the theoretical maximum gastrointestinal concentration to IC50 is sufficient for a reasonable prediction for these orally administered drugs as potential P‐gp inhibitors based on our dataset. The FN and FP rates varied depending on the cut‐off value for the ratio of the theoretical maximum gastrointestinal concentration/IC50. Possible reasons underlying FP and FN results from different methods should be taken into consideration to predict in vivo P‐gp inhibition. [ABSTRACT FROM AUTHOR]

Different views appear in the literature on the extent of specific cytochrome P450 (CYP) involvement in methadone metabolism. The aim of this work is to leverage knowledge from drug‐drug interaction (DDI) studies in new drug applications between methadone and antiviral medications to better understand methadone disposition and to inform design of future DDI studies with methadone. A database of DDI studies between all FDA‐approved human immunodeficiency virus and hepatitis C virus medications and methadone was constructed. The database contains data from 29 DDI studies. Sixteen of the 29 studies had statistically significant changes in methadone area under the concentration‐time curve. Methadone exposure was either decreased or unchanged when it was coadministered with weak to strong CYP3A inhibitors or a moderate CYP3A4 inducer. Methadone exposure was reduced when it was coadministered with CYP2B6 inducers. The role of other enzymes (CYP2C9, CYP2C19, and CYP2D6) cannot be fully elucidated from these studies. In conclusion, CYP2B6 plays a prominent role in methadone metabolism, although methadone exposure is not sensitive to CYP3A perturbation. In designing methadone DDI studies, (1) measuring R‐ and S‐methadone is more informative than measuring total methadone, and (2) CYP2B6 genotyping of subjects enrolled in methadone DDI studies should be considered. Finally, there is a need for the development of predictive models to determine the influence of medications on methadone disposition. [ABSTRACT FROM AUTHOR]

Aims: A dramatic increase in newborn infants with neonatal abstinence syndrome has been observed and these neonates are frequently treated with complex methadone dosing schemes to control their withdrawal symptoms. Despite its abundant use, hardly any data on the pharmacokinetics (PK) of methadone is available in preterm neonates. Therefore we investigated developmental PK of methadone and evaluated current dosing strategies and possible simplification in this vulnerable population. Methods: A single‐centre open‐label prospective study was performed to collect PK data after a single oral dose of methadone in preterm neonates. A population PK model was built to characterize developmental PK of (R)‐ and (S)‐methadone. Model‐based simulations were performed to identify a simplified dosing strategy to reach and maintain target methadone exposure. Results: A total of 121 methadone concentrations were collected from 31 preterm neonates. A one‐compartment model with first order absorption and elimination kinetics best described PK data for (R)‐ and (S)‐methadone. Clearance increases with advancing gestational age and differs between R‐ and S‐enantiomer, being slightly higher for the former (0.244 vs 0.167 L/h). Preterm neonates reached target exposure after 48 hours with currently used dosing schedules. Output from simulations revealed that target exposures can be achieved with a simplified dosing strategy during the first 4 days of treatment. Conclusion: Methadone clearance in preterm neonates increases with advancing gestational age and its disposition is influenced by its chirality. Simulations that account for developmental PK changes indicate a shorter methadone dosing strategy can maintain target exposure to control withdrawal symptoms. [ABSTRACT FROM AUTHOR]

Although current quetiapine labeling recommends that its dosage should be lowered 6‐fold when coadministered with strong cytochrome P450 (CYP)3A inhibitors, a reported case of coma in a patient receiving quetiapine with lopinavir and ritonavir prompted the reevaluation of labeling recommendations for the dosing of quetiapine when coadministered with human immunodeficiency virus (HIV) protease inhibitors. Literature and database (FDA Adverse Event Reporting System and United States Symphony Health Solutions' Integrated Dataverse Database) searches allowed us to identify cases of coma and related adverse events involving the coadministration of quetiapine and HIV protease inhibitors and to estimate the frequency of concomitant use. Literature review and physiologically based pharmacokinetic modeling allowed us to estimate the potential for CYP3A inhibition to contribute to adverse events related to HIV protease inhibitor–quetiapine coadministration. We identified excess sedation following coadministration of quetiapine and an HIV protease inhibitor in 3 reports without obvious confounders. In prescription claims data, 0.4% of quetiapine patients were dispensed a concurrent ritonavir prescription. The quetiapine dose was not reduced on ritonavir initiation in 90% of therapy episodes. Available data indicate to us that all HIV protease inhibitors combined with ritonavir are likely to be strong CYP3A inhibitors. We predicted that ritonavir would increase quetiapine exposure comparable to the strong CYP3A inhibitor ketoconazole. The current dosing recommendations for use of quetiapine with strong CYP3A inhibitors (ie, 6‐fold lower quetiapine dose) are appropriate and should be followed when quetiapine is coadministered with HIV protease inhibitors. [ABSTRACT FROM AUTHOR]

Aims: The present study evaluated the placental transfer and amniotic fluid distribution of bupivacaine enantiomers in health pregnant women and in human immunodeficiency virus (HIV)‐infected pregnant women receiving epidural anaesthesia for caesarean section. Methods: Twelve HIV‐infected pregnant women (HIV group) were treated long‐term (at least 8 weeks) with lopinavir/ritonavir (400/100 mg twice daily), and 12 healthy pregnant women (Control group) who submitted to epidural anaesthesia with racemic bupivacaine (75 mg) during caesarean section were investigated. At delivery, samples of maternal and fetal blood and amniotic fluid were collected (10–20 min after drug administration). Results: The placental transfer ratio of bupivacaine enantiomers was significantly higher among the pregnant women from the HIV group when compared with those from the Control group (Mann–Whitney test, P ≤ 0.05). Placental transfer ratios (median and 25th ‐ 75th percentiles) for (+)‐(R)‐bupivacaine were 0.58 (0.38–0.82) in the HIV group vs. 0.25 (0.18–0.33) in the Control group, and for (–)‐(S)‐bupivacaine, they were 0.54 (0.34–0.69) in the HIV group vs. 0.25 (0.19–0.29) in the Control group. The transplacental distribution of bupivacaine was stereoselective only in the HIV group. The umbilical artery/umbilical vein ratio and amniotic fluid/maternal vein ratio were low and nonstereoselective, and no statistically significant differences were observed between the groups. Conclusions: This study supports that the placental transfer of both bupivacaine enantiomers was 100% higher in HIV‐pregnant women treated with lopinavir/ritonavir when compared with that in healthy pregnant women receiving epidural anaesthesia for caesarean section. [ABSTRACT FROM AUTHOR]

Whether the combined use of probe drugs for CYP3A4 and P-glycoprotein can clarify the relative contribution of these proteins to pharmacokinetic variability of a dual substrate like tacrolimus has never been assessed. Seventy renal recipients underwent simultaneous 8-h pharmacokinetic profiles for tacrolimus, the CYP3A4 probe midazolam, and the putative P-glycoprotein probe fexofenadine. Patients were genotyped for polymorphisms in CYP3A5, CYP3A4, ABCB1, ABCC2 and SLCO2B1, - 1B1, and 1B3. Carriers of the ABCB1 2677G>A polymorphism displayed lower fexofenadine Cmax (-66%; P = 0.012) and a trend toward higher clearance (+157%; P = 0.078). Predictors of tacrolimus clearance were CYP3A5 genotype, midazolam clearance, hematocrit, weight, and age (R2 = 0.61). Fexofenadine pharmacokinetic parameters were not predictive of tacrolimus clearance. In conclusion, fexofenadine pharmacokinetics varied considerably between renal recipients but most of this variability remained unexplained, with only minor effects of genetic polymorphisms. Fexofenadine cannot be used to assess in vivo CYP3A4-P-glycoprotein interplay in tacrolimus-treated renal recipients. [ABSTRACT FROM AUTHOR]

Methadone is a cornerstone therapy for opioid addiction and a public health strategy for HIV/AIDS and hepatitis C reduction. Methadone is also used for acute and chronic pain. As use for chronic pain has grown, so too have adverse events. Constitutive and acquired (drug interactions) inter- and intraindividual variability in methadone pharmacokinetics and pharmacodynamics confounds reliable clinical use. Identification of enzymes and transporters responsible for methadone disposition has been a long-sought ideal. Initial in vitro studies identified CYP3A4 as metabolizing methadone. Subsequently, by extrapolation, CYP3A4 was long assumed to be responsible for clinical methadone disposition. However, CYP2B6 is also a major catalyst of methadone metabolism in vitro. It has now been unequivocally established that CYP2B6, not CYP3A4, is the principal determinant of methadone metabolism, clearance, elimination, and plasma concentrations in humans. Methadone disposition is susceptible to inductive and inhibitory drug interactions. CYP2B6 genetics also influences methadone metabolism and clearance, which were diminished in CYP2B6*6 carriers and increased in CYP2B6*4 carriers. CYP2B6 genetics can explain, in part, interindividual variability in methadone metabolism and clearance. Thus, both constitutive variability due to CYP2B6 genetics, and CYP2B6-mediated drug interactions, can alter methadone disposition, clinical effect, and drug safety. Methadone is not a substrate for major influx or efflux transporters. [ABSTRACT FROM AUTHOR]

Aims Oxidative bioactivation of amodiaquine (AQ) by cytochrome P450s to a reactive quinoneimine is considered as an important mechanism underlying its idiosyncratic hepatotoxicity. However, because internal exposure to its major metabolite N-desethylamodiaquine (DEAQ) is up to 240-fold higher than AQ, bioactivation of DEAQ might significantly contribute to covalent binding. The aim of the present study was to compare the kinetics of bioactivation of AQ and DEAQ by human liver microsomes (HLM) and to characterize the CYPs involved in bioactivation of AQ and DEAQ. Methods Glutathione was used to trap reactive metabolites formed in incubations of AQ and DEAQ with HLM and recombinant human cytochrome P450s (hCYPs). Kinetics of bioactivation of AQ and DEAQ in HLM and involvement of hCYPs were characterized by measuring corresponding glutathione conjugates (AQ-SG and DEAQ-SG) using a high-performance liquid chromatography method. Results Bioactivation of AQ and DEAQ in HLM both exhibited Michaelis-Menten kinetics. For AQ bioactivation, enzyme kinetical parameters were K m, 11.5 ± 2.0 μmol l-1, V max , 59.2 ± 3.2 pmol min−1 mg−1 and CL int, 5.15 μl min−1 mg−1. For DEAQ, parameters for bioactivation were K m, 6.1 ± 1.3 μmol l-1, V max , 5.5 ± 0.4 pmol min−1 mg−1 and CL int 0.90 μl min−1 mg−1. Recombinant hCYPs and inhibition studies with HLM showed involvement of CYP3A4, CYP2C8, CYP2C9 and CYP2D6 in bioactivation. Conclusions The major metabolite DEAQ is likely to be quantitatively more important than AQ with respect to hepatic exposure to reactive metabolites in vivo. High expression of CYP3A4, CYP2C8, CYP2C9, and CYP2D6 may be risk factors for hepatotoxicity caused by AQ-therapy. [ABSTRACT FROM AUTHOR]

This report describes phase 1 clinical trials performed to assess interactions of oral isavuconazole at the clinically targeted dose (200 mg, administered as isavuconazonium sulfate 372 mg, 3 times a day for 2 days; 200 mg once daily [QD] thereafter) with single oral doses of the cytochrome P450 (CYP) substrates: bupropion hydrochloride (CYP2B6; 100 mg; n = 24), repaglinide (CYP2C8/CYP3A4; 0.5 mg; n = 24), caffeine (CYP1A2; 200 mg; n = 24), dextromethorphan hydrobromide (CYP2D6/CYP3A4; 30 mg; n = 24), and methadone (CYP2B6/CYP2C19/CYP3A4; 10 mg; n = 23). Compared with each drug alone, coadministration with isavuconazole changed the area under the concentration-time curves (AUC∞) and maximum concentrations (Cmax) as follows: bupropion, AUC∞ reduced 42%, Cmax reduced 31%; repaglinide, AUC∞ reduced 8%, Cmax reduced 14%; caffeine, AUC∞ increased 4%, Cmax reduced 1%; dextromethorphan, AUC∞ increased 18%, Cmax increased 17%; R-methadone, AUC∞ reduced 10%, Cmax increased 3%; S-methadone, AUC∞ reduced 35%, Cmax increased 1%. In all studies, there were no deaths, 1 serious adverse event (dextromethorphan study; perioral numbness, numbness of right arm and leg), and adverse events leading to study discontinuation were rare. Thus, isavuconazole is a mild inducer of CYP2B6 but does not appear to affect CYP1A2-, CYP2C8-, or CYP2D6-mediated metabolism. [ABSTRACT FROM AUTHOR]

The article presents ritonavir as preferable to itraconazole as index CYP3A inhibitor for drug-drug interaction (DDI) studies in healthy volunteers. It cites cobicistat which is similar in structure and pharmacologic properties of ritonavir although clinical experience with cobicistat as a single-entity boosting agent is more limited than that with ritonavir. It points out that cobicistat can be considered an option to serve as an index CYP3A inhibitor.

Aims The regulatory prohibition of ketoconazole as a CYP3A index inhibitor in drug-drug interaction (DDI) studies has compelled consideration of alternative inhibitors. Methods The biomedical literature was searched to identify DDI studies in which oral midazolam (MDZ) was the victim, and the inhibitory perpetrator was either ketoconazole, itraconazole, clarithromycin, or ritonavir. The ratios (RAUC) of total area under the curve (AUC) for MDZ with inhibitor divided by MDZ AUC in the control condition were aggregated across individual studies for each inhibitor. Results Mean (± SE) RAUC values were: ketoconazole (15 studies, 131 subjects), 11.5 (±1.2); itraconazole (five studies, 48 subjects), 7.3 (±1.0); clarithromycin (five studies, 73 subjects), 6.5 (±10.9); and ritonavir (13 studies, 159 subjects), 14.5 (±2.0). Differences among inhibitors were significant ( F = 5.31, P < 0.005). RAUC values were not significantly related to inhibitor dosage or to duration of inhibitor pre-exposure prior to administration of MDZ. Conclusions Ritonavir produces CYP3A inhibition equivalent to or greater than ketoconazole, and is the best index CYP3A inhibitor alternative to ketoconazole. Cobicistat closely resembles ritonavir in structure and function, and can also be considered. Itraconazole and clarithromycin are not suitable alternatives since they do not produce inhibition comparable with ketoconazole or ritonavir, and have other significant disadvantages as well. [ABSTRACT FROM AUTHOR]

Aim Recognition of normal and abnormal heart sounds and murmurs is an important but declining clinical skill among practitioners. Current teaching methods are often ineffective. This may result from inadequate repetition and normal-abnormal comparisons needed for auditory recognition. This paper describes a rapid new method of teaching murmur recognition using principles of auditory training. Methods Participants were 120 Australian and 42 Canadian medical students. The medical students were randomised to intervention and control (no intervention) groups. The 1-h online programme structured like a computer game used auditory training methodology to teach students to distinguish between innocent and pathological murmurs. Participants underwent pre- and post-testing on 20 paediatric murmurs. Post-testing occurred immediately following training and after 2 months. Twenty-two Canadian medical students were retested 1 year later with a brief mastery-style reinforcement programme. Results Median pre- and post-test scores improved in about 1 h from 75-95% ( P < 0.001) for Australian students and 85-95% ( P = 0.004) for Canadian students. Two-month post-test scores declined for Australian students to 85% ( P = 0.001), and for Canadian students to 85% ( P = 0.02). Australian controls had no significant change during the study period, whereas Canadian controls improved slightly. The group receiving reinforcement after 1 year had a median final score of 90%. Conclusions This auditory training programme rapidly teaches students to distinguish innocent and pathological murmurs with at least 90% accuracy. The skill declines within 2 months but can be restored with brief mastery reinforcement 1 year later. [ABSTRACT FROM AUTHOR]

Dose-associated effects of rosuvastatin on the metabolism of apolipoprotein (apo) B-100 in triacylglycerol rich lipoprotein (TRL, d < 1.019 g/ml) and low density lipoprotein (LDL) and of apoA-I in high density lipoprotein (HDL) were assessed in subjects with combined hyperlipidemia. Our primary hypothesis was that maximal dose rosuvastatin would decrease the apoB-100 production rate (PR), as well as increase apoB-100 fractional catabolic rate (FCR). Eight subjects received placebo, rosuvastatin 5 mg/day, and rosuvastatin 40 mg/day for 8 weeks each in sequential order. The kinetics of apoB-100 in TRL and LDL and apoA-I in HDL were determined at the end of each phase using stable isotope methodology, gas chromatography-mass spectrometry, and multicompartmental modeling. Rosuvastatin at 5 and 40 mg/day decreased LDL cholesterol by 44 and 54 % (both P < 0.0001), triacylglycerol by 14 % (ns) and 35 % ( P < 0.01), apoB by 30 and 36 % (both P < 0.0001), respectively, and had no significant effects on HDL cholesterol or apoA-I levels. Significant decreases in plasma markers of cholesterol synthesis and increases in cholesterol absorption markers were observed. Rosuvastatin 5 and 40 mg/day increased TRL apoB-100 FCR by 36 and 46 % (both ns) and LDL apoB-100 by 63 and 102 % (both P < 0.05), respectively. HDL apoA-I PR increased with low dose rosuvastatin (12 %, P < 0.05) but not with maximal dose rosuvastatin. Neither rosuvastatin dose altered apoB-100 PR or HDL apoA-I FCR. Our data indicate that maximal dose rosuvastatin treatment in subjects with combined hyperlipidemia resulted in significant increases in the catabolism of LDL apoB-100, with no significant effects on apoB-100 production or HDL apoA-I kinetics. [ABSTRACT FROM AUTHOR]

Atrial septal defect (ASD) is the most common congenital heart defect clinically characterized by an opening in the atrial septum. Mutations in GATA4, TBX5, and NKX2-5 underlie this phenotype. Here, we report on the identification of a novel -6 G > C mutation in the highly conserved Kozak sequence in the 5'UTR of GATA4 in a small family presenting with two different forms of ASD. This is the first time a mutation in the Kozak sequence has been linked to heart disease. Functional assays demonstrate reduced GATA4 translation, though the GATA4 transcript levels remain normal. This leads to a reduction of GATA4 protein level, consequently diminishing the ability of GATA4 to transactivate target genes, as demonstrated by using the GATA4-driven Nppa (ANF) promoter. In conclusion, we identified a mutation in the GATA4 Kozak sequence that likely contributes to the pathogenesis of ASD. In general, it points to the importance of accurate protein level regulation during heart development and emphasizes the need to analyze the entire transcribed region when screening for mutations. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Atherogenic dyslipidaemia is a hypertriglyceridaemic phenotype, associated with increased plasma concentrations of small, dense low-density lipoprotein ( sdLDL) particles, triglyceride-rich lipoproteins ( TRLs) and non-high-density lipoprotein cholesterol (non- HDL-C), and low HDL particles. Atherogenic dyslipidaemia commonly accompanies several metabolic disorders including type 2 diabetes, metabolic syndrome, non-alcoholic fatty liver disease ( NAFLD) and obesity, and increases the risk of cardiovascular disease ( CVD). Statins significantly lower plasma LDL-cholesterol and CVD risk, but their efficacy in correcting hypertriglyceridaemia is limited. Untreated hypertriglyceridaemia may partly account for residual risk of CVD in patients on statin treatment. Activators of peroxisome proliferator-activated receptor ( PPAR) α are more effective in correcting TRL and HDL metabolism than statins. A dual PPARα/δ agonist ( GFT-505) may have additional benefits on hepatic insulin sensitivity, steatosis and fibrosis. Selective PPAR modulators ( SPPARMs) have the potential of increasing therapeutic specificity, while reducing unwanted off-target effects. This review provides a summary of findings from randomized controlled trials of the efficacy of fenofibrate (as the most widely used PPARα agonist) and novel selective PPARα ( ABT-335 and k-877), PPARα/δ ( GFT-505), PPARδ ( MBX-8025 and GW501516) and PPARγ ( INT131) agonists in the treatment of atherogenic dyslipidaemia and NAFLD. [ABSTRACT FROM AUTHOR]

RATIONALE Apolipoprotein(a) is a polymorphic glycoprotein covalently bound to apoB100 in Lp(a) particles and has been described to be both atherogenic and prothrombotic, although its exact mechanism of action is not well defined. Apolipoprotein(a) is routinely measured by immunoassays. Unfortunately, the accuracy of the measurement can be affected by the apolipoprotein(a) size (number of kringles) polymorphism in Lp(a) particles. Here we describe an ultra-performance liquid chromatography/mass spectrometry (UPLC/MS) assay that is capable of measuring apolipoprotein(a) concentrations while simultaneously determining the number of kringles present per protein. METHODS Plasma samples were diluted and proteins de-lipidated with deoxycholate prior to tryptic digestion. Distinct tryptic peptides from different regions of apolipoprotein(a) were measured to determine both concentration and the number of kringles present per protein. Separation and quantitation of tryptic peptides is carried out at 700 μL/min using a 1.7 µm C18 column (2.1 × 100 mm) coupled to a Thermo Vantage triple quadrupole (QQQ) mass spectrometer with a heated electrospray ionization (HESI) source. RESULTS This method was compared to established methods for measuring concentration (monoclonal antibody based ELISA) and size (gel-electrophoresis) using 80 plasma samples proved by NWLRL. The slope and r2 value for the correlation of concentrations were determined to be 0.96 and 0.98, demonstrating excellent agreement of absolute values between the UPLC/MS and ELISA methods. As measured by UPLC/MS, the average kringle number or size is smaller than determined by the electrophoretic method. CONCLUSIONS A single UPLC/MS method was developed capable of measuring apolipoprotein(a) concentration and size (by measuring the number of kringles per protein). This assay passes criteria required for 'fit for purpose' assays including sensitivity, intra and interday reproducibility and freeze/thaw stability. While the agreement between UPLC/MS and ELISA is excellent for concentration and may provide researchers with additional tools for studying apolipoprotein(a), the dissimilarities between UPLC/MS and the electrophoretic method may also be exploited for understanding apolipoprotein(a) structure and function. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Aim Conducting PK studies in pregnant women is challenging. Therefore, we asked if a physiologically-based pharmacokinetic ( PBPK) model could be used to predict the disposition in pregnant women of drugs cleared by multiple CYP enzymes. Methods We expanded and verified our previously published pregnancy PBPK model by incorporating hepatic CYP2B6 induction (based on in vitro data), CYP2C9 induction (based on phenytoin PK) and CYP2C19 suppression (based on proguanil PK), into the model. This model accounted for gestational age-dependent changes in maternal physiology and hepatic CYP3A, CYP1A2 and CYP2D6 activity. For verification, the pregnancy-related changes in the disposition of methadone (cleared by CYP2B6, 3 A and 2C19) and glyburide (cleared by CYP3A, 2C9 and 2C19) were predicted. Results Predicted mean post-partum to second trimester ( PP : T2) ratios of methadone AUC, Cmax and Cmin were 1.9, 1.7 and 2.0, vs. observed values 2.0, 2.0 and 2.6, respectively. Predicted mean post-partum to third trimester ( PP : T3) ratios of methadone AUC, Cmax and Cmin were 2.1, 2.0 and 2.4, vs. observed values 1.7, 1.7 and 1.8, respectively. Predicted PP : T3 ratios of glyburide AUC, Cmax and Cmin were 2.6, 2.2 and 7.0 vs. observed values 2.1, 2.2 and 3.2, respectively. Conclusions Our PBPK model integrating prior physiological knowledge, in vitro and in vivo data, allowed successful prediction of methadone and glyburide disposition during pregnancy. We propose this expanded PBPK model can be used to evaluate different dosing scenarios, during pregnancy, of drugs cleared by single or multiple CYP enzymes. [ABSTRACT FROM AUTHOR]

Study Objective To investigate the steady-state pharmacokinetics of methadone when coadministered with ritonavir-boosted danoprevir ( DNVr). Design Open-label, two-period, single-sequence pharmacokinetic study. Setting Two U. S. research centers. Patients Eighteen methadone-maintained healthy adults. Measurements and Main Results In Period 1 (Day −1), subjects received their daily methadone maintenance therapy ( MMT). In Period 2 (Days 1-10), subjects received MMT plus DNVr 100/100 mg twice/day. Pharmacokinetic parameters for the total concentrations of ( R)- and ( S)-methadone on Days −1 and 10 were determined using noncompartmental methods. Unbound ( R)- and ( S)-methadone concentrations at 3 hours postdose were also assessed on Days −1 and 10. Geometric mean ratios ( GMRs) and 90% confidence intervals ( CIs) were used to compare steady-state ( R)- and ( S)-methadone pharmacokinetics when MMT was administered with or without DNVr. Methadone withdrawal was assessed using the Subjective Opiate Withdrawal Scale. Compared with MMT alone, methadone AUCtau and Cmax GMR (90% CI) following coadministration with DNVr were 1.02 (0.91-1.15) and 1.01 (0.90-1.13) for ( R)-methadone, and 1.01 (0.90-1.13) and 0.99 (0.89-1.10) for ( S)-methadone, respectively. Unbound ( R- and ( S)-methadone concentrations were comparable with or without DNVr. No instances of methadone withdrawal were reported. MMT in combination with DNVr was well tolerated. Conclusion Coadministration of DNVr with MMT resulted in no significant pharmacokinetic interactions or signs of methadone withdrawal. No dosage adjustment is needed for MMT when coadministered with DNVr. [ABSTRACT FROM AUTHOR]

Antiretrovirals may influence methadone exposure in HIV-1-infected patients receiving methadone for opiate addiction. Rilpivirine is a non-nucleoside reverse transcriptase inhibitor for treating HIV-1 infection. In this open-label trial (NCT00744770), 13 HIV-negative volunteers continued on their regular stable methadone therapy (60 to 100 mg once daily; Days −14 to 12), with rilpivirine coadministration (Days 1 to 11). Methadone and rilpivirine pharmacokinetics and opiate withdrawal symptoms (Short Opiate Withdrawal Scale, Desires for Drugs Questionnaire, pupillometry) were evaluated. Rilpivirine decreased methadone minimum and maximum plasma concentrations (Cmin; Cmax) and area under the plasma concentration-time curve versus methadone alone (least-square mean ratio; 90% confidence interval) by 22% (0.78; 0.67, 0.91), 14% (0.86; 0.78, 0.95), and 16% (0.84; 0.74, 0.95), respectively (R-methadone), and 21% (0.79; 0.67, 0.92), 13% (0.87; 0.78, 0.97), and 16% (0.84; 0.74, 0.96), respectively (S-methadone). Rilpivirine pharmacokinetics with methadone were consistent with historic data. No clinically relevant opiate withdrawal symptoms were reported. Methadone and rilpivirine coadministration was generally well tolerated. No grade 3/4 adverse events (AEs), serious AEs, or discontinuations due to AEs were seen. No methadone dose adjustment is prompted by rilpivirine coadministration. Clinical monitoring for opiate withdrawal is recommended, as some patients may require adjustment of methadone maintenance therapy. [ABSTRACT FROM AUTHOR]

ABSTRACT Adequate methadone dosing in methadone maintenance treatment (MMT) for opioid addiction is critical for therapeutic success. One of the challenges in dose determination is the inter-individual variability in dose-response. Methadone metabolism is attributed primarily to cytochrome P450 enzymes CYP3A4, CYP2B6 and CYP2D6. The CYP2B6* 6 allele [single nucleotide polymorphisms (SNPs) 785A>G (rs2279343) and 516G>T (rs3745274)] was associated with slow methadone metabolism. To explore the effects of CYP2B6* 6 allele on methadone dose requirement, it was genotyped in a well-characterized sample of 74 Israeli former heroin addicts in MMT. The sample is primarily of Middle Eastern/European ancestry, based on ancestry informative markers (AIMs). Only patients with no major co-medication that may affect methadone metabolism were included. The stabilizing daily methadone dose in this sample ranges between 13 and 260 mg (mean 140 ± 52 mg). The mean methadone doses required by subjects homozygous for the variant alleles of the CYP2B6 SNPs 785A>G and 516G>T (88, 96 mg, respectively) were significantly lower than those of the heterozygotes (133, 129 mg, respectively) and the non-carriers (150, 151 mg, respectively) (nominal P = 0.012, 0.048, respectively). The results remain significant after controlling for age, sex and the ABCB1 SNP 1236C>T (rs1128503), which was previously shown to be associated with high methadone dose requirement in this population ( P = 0.006, 0.030, respectively). An additional 77 CYP2B6, CYP3A4 and CYP2D6 SNPs were genotyped. Of these, 24 SNPs were polymorphic and none showed significant association with methadone dose. Further studies are necessary to replicate these preliminary findings in additional subjects and other populations. [ABSTRACT FROM AUTHOR]

RATIONALE Apolipoprotein(a) [apo(a)] is the defining protein component of lipoprotein(a) [Lp(a)], an independent risk factor for cardiovascular disease. The regulation of Lp(a) levels in blood is poorly understood in part due to technical challenges in measuring Lp(a) kinetics. Improvements in the ability to readily and reliably measure the kinetics of apo(a) using a stable isotope labeled tracer is expected to facilitate studies of the role of Lp(a) in cardiovascular disease. Since investigators typically determine the isotopic labeling of protein-bound amino acids following acid-catalyzed hydrolysis of a protein of interest [e.g., apo(a)], studies of protein synthesis require extensive protein purification which limits throughput and often requires large sample volumes. We aimed to develop a rapid and efficient method for studying apo(a) kinetics that is suitable for use in studies involving human subjects. METHODS Microfluidic device and tandem mass spectrometry were used to quantify the incorporation of [2H3]-leucine tracer into protein-derived peptides. RESULTS We demonstrated that it is feasible to quantify the incorporation of [2H3]-leucine tracer into a proteolytic peptide from the non-kringle repeat region of apo(a) in human subjects. Specific attention was directed toward optimizing the multiple reaction monitoring (MRM) transitions, mass spectrometer settings, and chromatography (i.e., critical parameters that affect the sensitivity and reproducibility of isotopic enrichment measurements). The results demonstrated significant advantages with the use of a microfluidic device technology for studying apo(a) kinetics, including enhanced sensitivity relative to conventional micro-flow chromatography, a virtually drift-free elution profile, and a stable and robust electrospray. CONCLUSIONS The technological advances described herein enabled the implementation of a novel method for studying the kinetics of apo(a) in human subjects infused with [2H3]-leucine. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We investigated the mechanisms of ritonavir-mediated enhancement effect on the pharmacokinetics of saquinavir using in vivo probes for CYP3A4 (midazolam), p-glycoprotein (fexofenadine), and OATP1B1 (pravastatin) following oral micro/small dosing. A cocktail of the drugs (2 mg of saquinavir, 100 µg of each probe) was administered to eight healthy volunteers (phase 1), and then coadministered with 20 mg (phase 2) and 100 mg (phase 3) of ritonavir. Plasma concentrations of the drugs were measured by validated LC-MS/MS methods. The mean plasma AUC0-24 (pg hour/mL) of saquinavir at phases 1, 2, and 3 was 101, 2 540, and 23 900 ( P < .01), respectively. The relative area under the plasma concentration-time curve (AUC)0-24 ratios of midazolam and fexofenadine at phases 1, 2, and 3 were 1:5.9:14.7 ( P < .01), and 1:1.4:2.2 ( P < .01-.05), respectively. In contrast, there was no difference in the pharmacokinetics of pravastatin. Inhibition of intestinal and hepatic CYP3A-mediated metabolism, and intestinal p-glycoprotein-mediated efflux of saquinavir, but not OATP1B1, is involved in the enhancement mechanism. Micro/small dosing is useful for examining the mechanism of drug interactions without safety concern. [ABSTRACT FROM AUTHOR]

Methadone N-demethylation in vitro is catalyzed by hepatic cytochrome P4502B6 (CYP2B6) and CYP3A4, but clinical disposition is often attributed to CYP3A4. This investigation tested the hypothesis that CYP2B6 is a prominent CYP isoform responsible for clinical methadone N-demethylation and clearance, using the in vivo mechanism-based CYP2B6 inhibitor ticlopidine, given orally for 4 days. A preliminary clinical investigation with the CYP3A4/5 substrate probe alfentanil established that ticlopidine did not inhibit intestinal or hepatic CYP3A4/5. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone before and after ticlopidine. Ticlopidine significantly and stereoselectively (S > R) inhibited methadone N-demethylation, decreasing plasma metabolite/methadone area under the curve ratios and metabolite formation clearances. Ticlopidine also significantly increased the dose-adjusted plasma area under the curve for R- and S-methadone by 20% and 60%, respectively, after both intravenous and oral dosing. CYP2B6 inhibition reduces methadone N-demethylation and clearance, and alters methadone concentrations, demonstrating an important role for CYP2B6 in clinical methadone disposition. [ABSTRACT FROM AUTHOR]

LDL, total cholesterol (TC), high-density lipoprotein (HDL) are poor predictors of the cardiovascular risk among patients undergoing hypolipidaemic therapy with statins. Thus, in this pilot study we have attempted to determine, on the basis of routinely used assessments of lipid profiles, sensitive and inexpensive parameter which would associate with the severity of coronary artery disease in patients undergoing hypolipidaemic treatment who achieved LDL goal. Apolipoprotein (apo) B100, apoA1, LDL, triglycerides, HDL, lipoprotein (a) and TC levels were assessed in 140 patients referred for coronary angiography. The various ratios based on lipid parameters were calculated and compared to patients taking statins. Coronary arteriosclerosis was determined by the degree of single stenosis and quantitatively by applying the Gensini score. Uing multivariate analysis we have found that in the group with hypolipidaemic therapy and/or with treatment LDL target (70-100 mg/dL) the TC/apoB100 ratio was associated with coronary artery stenosis. Additionally, univariate analysis showed that the TC/apoB100 ratio (among treated subjects) was significantly lower in patients with haemodynamically significant stenosis of coronary arteries than in matched patients without coronary artery lesions. [ABSTRACT FROM AUTHOR]

Systemic and oral clearances of alfentanil (ALF) are in vivo probes for hepatic and first-pass cytochrome P450 (CYP) 3A. Both ALF single-point plasma concentrations and miosis are surrogates for area under the concentration-time curve (AUC) and clearance and are minimal and noninvasive CYP3A probes. This investigation determined ALF sensitivity for detecting graded CYP3A induction and compared it with that of midazolam (MDZ). Twelve volunteers (sequential crossover) received 0, 5, 10, 25, or 75 mg oral rifampin for 5 days. MDZ and ALF were given intravenously and orally on sequential days. Dark-adapted pupil diameter was measured with blood sampling. Graded rifampin decreased plasma MDZ AUCs to 83, 76, 62, and 59% (intravenous (i.v.)) and 78, 66, 39, and 24% (oral) of control. Hepatic and first-pass CYP3A induction were detected comparably by plasma MDZ and ALF AUCs. Single ALF concentrations detected all CYP3A induction, whereas MDZ was less sensitive. ALF miosis detected induction of first-pass but not hepatic CYP3A. [ABSTRACT FROM AUTHOR]

Alfentanil (ALF) is a validated probe for hepatic, first-pass, and intestinal cytochrome P450 (CYP) 3A activity, using plasma clearances, single-point concentrations, and noninvasive pupil diameter change (miosis). Assessing intravenous (i.v.) and oral drug disposition typically requires separate dosing. This investigation evaluated concurrent administration of oral deuterated and i.v. unlabeled ALF to assess both intestinal and hepatic CYP3A, and compare sequential and simultaneous dosing. ALF disposition was evaluated after strong hepatic and/or intestinal CYP3A induction and inhibition by rifampin, ketoconazole, and grapefruit juice. Using plasma ALF concentrations and area under the curve (AUC), clearance, or single-point concentrations, both simultaneous and sequential dosing provided equivalent results and detected hepatic and intestinal CYP3A induction and inhibition. Miosis better detected CYP3A modulation with sequential vs. simultaneous dosing. These results show that concurrent administration of oral deuterated and i.v. ALF, either sequentially or simultaneously, is an efficient and effective approach to assessing hepatic and intestinal CYP3A activity. [ABSTRACT FROM AUTHOR]

The article reports on two drug-drug interaction studies in opioid maintenance therapy in the context of providing guidance for safe dose recommendations. The discussion focuses on the effects of various doses of darunavir and ritonavir on the steady-state pharmacokinetics of methadone, buprenorphine, and naloxone.

In vitro metabolism of methadone was investigated in cytochrome P450 (CYP) supersomes and phenotyped human liver microsomes (HLMs) to reconcile past findings on CYP involvement in stereo-selective metabolism of methadone. Racaemic methadone was used for incubations; ( R)- and ( S)-methadone turnover and ( R)- and ( S)-EDDP formation were determined using chiral liquid chromatography-tandem mass spectrometry. CYP supersome activity for methadone use and EDDP formation ranked CYP2B6 > 3A4 > 2C19 > 2D6 > 2C18, 3A7 > 2C8, 2C9, 3A5. After abundance scaling, CYP3A4, 2B6 and 2C19 accounted for 63-74, 12-32 and 1. 4-14% of respective activity. CYP2B6, 2D6 and 2C18 demonstrated a preference for ( S)-EDDP formation; CYP2C19, 3A7 and 2C8 for ( R)-EDDP; 3A4 none. Correlation analysis with 15 HLMs supported the involvement of CYP2B6 and 3A. The significant correlation of S/ R ratio with CYP2B6 activity confirmed its stereo-selectivity. CYP2C19 and 2D6 inhibitors and monoclonal antibody (mAb) did not inhibit EDDP formation in HLM. Chemical and mAb inhibition of CYP3A in high 3A activity HLM reduced EDDP formation by 60-85%; inhibition of CYP2B6 in 2B6 high-activity HLM reduced ( S)-EDDP formation by 80% and ( R)-EDDP formation by 55%. Inhibition changed methadone metabolism in a stereo-selective manner. When CYP3A was inhibited, 2B6 mediated ( S)-EDDP formation predominated; S/ R stereo-selectivity increased. When 2B6 was inhibited ( S)-EDDP formation fell and stereo-selectivity decreased. The results confirmed the primary roles of CYPs 3A4 and 2B6 in methadone metabolism; CYP2C8 and 2C9 did not appear involved; 2C19 and 2D6 have minimal roles. CYP2B6 is the primary determinant of stereo-selective metabolism; stereo-selective inhibition might play a role in varied plasma concentrations of the two enantiomers. [ABSTRACT FROM AUTHOR]