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Sofosbuvir (SOF) is a P-glycoprotein (P-gp) substrate, and carvedilol (CAR) is an inhibitor of P-gp, suggesting that it may affect the oral pharmacokinetics and safety of SOF. The current study investigated the pharmacokinetic interaction of CAR with SOF and its metabolite, GS-331007, and the possible consequent toxicities in rats. To assess the pharmacokinetics of SOF and GS-331007, rats were divided into three groups; all received a single oral dose of SOF preceded with saline (SAL), verapamil (VER) as a standard P-gp inhibitor, or CAR, respectively. The serosal, plasma, and hepatic tissue contents of SOF and GS-331007 were assessed using LC-MS/MS. Renal and hepatic toxicities were assessed using biochemical and histopathological tests. Serosal and plasma concentrations of SOF and GS-331007 were increased in the presence of CAR, suggesting a significant inhibitory effect of CAR on intestinal P-gp. Simultaneously, the pharmacokinetic profile of SOF showed a significant increase in the Cmax, AUC(0-t), AUC (0-∞), t1/2, and a reduction in its apparent oral clearance. While the pharmacokinetic profile of GS-331007 was not significantly affected. However, this notable elevation in drug oral bioavailability was corroborated by a significant alteration in renal functions. Hence, further clinical investigations are recommended to ensure the safety and dosing of CAR/SOF combination., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Royal Pharmaceutical Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Verapamil hydrochloride (VRP), an antihypertensive calcium channel blocker drug has limited bioavailability and short half-life when taken orally. The present study was aimed at developing cubosomes containing VRP for enhancing its bioavailability and targeting to brain for cluster headache (CH) treatment as an off-label use. Factorial design was conducted to analyze the impact of different components on entrapment efficiency (EE%), particle size (PS), zeta potential (ZP), and percent drug release. Various in-vitro characterizations were performed followed by pharmacokinetic and brain targeting studies. The results revealed the significant impact of glyceryl monooleate (GMO) on increasing EE%, PS, and ZP of cubosomes with a negative influence on VRP release. The remarkable effect of Poloxamer 407 (P407) on decreasing EE%, PS, and ZP of cubosomes was observed besides its influence on accelerating VRP release%. The DSC thermograms indicated the successful entrapment of the amorphous state of VRP inside the cubosomes. The design suggested an optimized formulation containing GMO (50% w/w) and P407 (5.5% w/w). Such formulation showed a significant increase in drug permeation through nasal mucosa with high E r value (2.26) when compared to VRP solution. Also, the histopathological study revealed the safety of the utilized components used in the cubosomes preparation. There was a significant enhancement in the VRP bioavailability when loaded in cubosomes owing to its sustained release favored by its direct transport to brain. The I.N optimized formulation had greater BTE% and DTP% at 183.53% and 90.19%, respectively in comparison of 41.80% and 59% for the I.N VRP solution., (© 2024. The Author(s).)

Background: Yunaconitine (YAC) is a hidden toxin that greatly threatens the life safety of patients who are prescribed herbal medicines containing Aconitum species; however, its underlying mechanism remains unclear., Objective: The objective of this study is to elucidate the functions of P-glycoprotein (P-gp) in regulating the efficacy, toxicity, and pharmacokinetics of YAC., Methods: The efflux function of P-gp on YAC was explored by using Caco-2 monolayers in combination with the P-gp inhibitor verapamil. The impact of P-gp on regulating the analgesic and anti-inflammatory effects, acute toxicity, tissue distribution, and pharmacokinetics of YAC was determined via male Mdr1a gene knocked-out mice and wild-type FVB mice., Results: The presence of verapamil significantly decreased the efflux ratio of YAC from 20.41 to 1.07 in Caco- 2 monolayers (P < 0.05). Moreover, oral administration of 0.07 and 0.14 mg/kg YAC resulted in a notable decrease in writhing times in Mdr1a -/- mice by 23.53% and 49.27%, respectively, compared to wild-type FVB mice (P < 0.05). Additionally, the deficiency of P-gp remarkably decreased the half-lethal dose (LD 50 ) of YAC from 2.13 to 0.24 mg/kg (P < 0.05). Moreover, the concentrations of YAC in the tissues of Mdr1a -/- mice were statistically higher than those in wild-type FVB mice (P < 0.05). Particularly, the brain accumulation of YAC in Mdr1a -/- mice significantly increased by 12- and 19-fold, respectively, after oral administration for 30 and 120 min, when compared to wild-type FVB mice (P < 0.05). There were no significant differences in the pharmacokinetic characteristics of YAC between Mdr1a -/- and wild-type FVB mice., Conclusion: YAC is a sensitive substrate of P-gp. The absence of P-gp enhances the analgesic effect and toxicity of YAC by upregulating its brain accumulation. Co-administration with a P-gp inhibitor may lead to severe YAC poisoning., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

This study investigated the ability of natural nanotubular clay mineral (Halloysite) and cellulose ether based biocomposite matrix as a controlled release agent for Verapamil HCl (BCS Class-I). Drug-loaded halloysite was prepared and tablet formulations were designed by varying amount of hydroxy propyl methyl cellulose (HPMC K4M). Physical characterization was carried out using SEM, FTIR, and DSC. Tabletability profiles were evaluated using USP1062 guidelines. Drug release kinetics were studied, and physiologically based pharmacokinetic (PBPK) modeling was performed. Compressed tablets possess satisfactory yield pressure of 625 MPa with adequate hardness and disintegration within 30 min. The initial release of the drug was due to surface drug on tablets, while the prolonged release at later time points (around 80 % drug release at 12 h) were due to halloysite loading. The FTIR spectra exhibited electrostatic attraction between the positively charged drug and the negatively charged Si-O-Si functional group of halloysite, while the thermogram showed Verapamil HCl melting point at ~146 °C with enthalpy change of -126.82 J/g. PBPK modeling exhibited PK parameters of optimized matrix formulation (VER-HNT 3% ) comparable to in vivo data. The study effectively demonstrated the potential of prepared biocomposite matrix as a commercially viable oral release modifying agent for highly soluble drugs., Competing Interests: Declaration of competing interest There is no conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Introduction: Drug-drug interaction (DDI) is one of the major concerns for the clinical use of NOACs in the older adults considering that coexistence of multiple diseases and comorbidity were common. Current guidelines on the DDI management were established based on clinical studies conducted in healthy adults and mainly focus on the Caucasians, whereas systemic and ethnic differences may lead to distinct management in the Chinese older adults., Objectives: To investigate the impact of aging on the DDI magnitude between P-gp and/or CYP3A4 inhibitors with dabigatran etexilate and rivaroxaban in older adults, providing additional information for the use in clinical practice., Results: Compared with the simulated adult, the AUC of the simulated older adults increased by 42-88% (DABE) and 21-60% (rivaroxaban), respectively, during NOACs monotherapy. Simulation on DDIs predicted that verapamil and clarithromycin further increase the exposure of dabigatran by 29-72% and 40-47%, whereas clarithromycin, fluconazole, and ketoconazole increase the exposure of rivaroxaban by 21-30%, 16-24%, and 194-247% in the older adults. Overall, our simulation result demonstrated that aging and DDIs both increased the exposure of NOACs. However, aging does not have a drastic impact on the extent of DDIs. The DDI ratios of young and old older adults were similar to the adults and were also similar between Caucasians and Chinese., Discussion: We further simulated the interactions under steady-state based on the EHRA guideline (2021). Our simulation results revealed that recommended reduced dosing regimen of dabigatran etexilate during comedication with verapamil and clarithromycin (110 and 75 mg BID for Chinese young and old older adults) will result in exposure (trough concentration) that was either slightly higher or similar to the trough concentration of patients with any bleeding events. Routine monitoring of bleeding risk is encouraged. Further studies on the use of rivaroxaban in Chinese older adults are warranted., Conclusion: Aging and DDI increases exposure of drug in Chinese older adults. However, aging does not have a drastic impact on the extent of DDIs. Clinical management of DDIs in Chinese older adults in the absence of complex polypharmacy can a priori be similar to the EHRA guideline but routine monitoring of bleeding risk is encouraged when dabigatran etexilate given with verapamil and clarithromycin., Competing Interests: Declaration of Competing Interest Valerie Sia Jie En, Xuan Lai, Xinyi Wu, Fan Zhang, Haiyan Li, Cheng Cui and Dongyang Liu declare that they have no potential conflicts of interest that might be relevant to the contents of this manuscript., (Copyright © 2023. Published by Elsevier B.V.)

Membrane permeability plays an important role in oral drug absorption. Caco-2 and Madin-Darby Canine Kidney (MDCK) cell culture systems have been widely used for assessing intestinal permeability. Since most drugs are absorbed passively, Parallel Artificial Membrane Permeability Assay (PAMPA) has gained popularity as a low-cost and high-throughput method in early drug discovery when compared to high-cost, labor intensive cell-based assays. At the National Center for Advancing Translational Sciences (NCATS), PAMPA pH 5 is employed as one of the Tier I absorption, distribution, metabolism, and elimination (ADME) assays. In this study, we have developed a quantitative structure activity relationship (QSAR) model using our ∼6500 compound PAMPA pH 5 permeability dataset. Along with ensemble decision tree-based methods such as Random Forest and eXtreme Gradient Boosting, we employed deep neural network and a graph convolutional neural network to model PAMPA pH 5 permeability. The classification models trained on a balanced training set provided accuracies ranging from 71% to 78% on the external set. Of the four classifiers, the graph convolutional neural network that directly operates on molecular graphs offered the best classification performance. Additionally, an ∼85% correlation was obtained between PAMPA pH 5 permeability and in vivo oral bioavailability in mice and rats. These results suggest that data from this assay (experimental or predicted) can be used to rank-order compounds for preclinical in vivo testing with a high degree of confidence, reducing cost and attrition as well as accelerating the drug discovery process. Additionally, experimental data for 486 compounds (PubChem AID: 1645871) and the best models have been made publicly available (https://opendata.ncats.nih.gov/adme/)., (Published by Elsevier Ltd.)

Cancer multi-drug resistance (MDR) caused by P-glycoprotein (P-gp) efflux is a critical unresolved clinical concern. The present study analyzed the effect of cinnamophilin on P-gp inhibition and MDR reversion. The effect of cinnamophilin on P-gp was investigated through drug efflux assay, ATPase assay, MDR1 shift assay, and molecular docking. The cancer MDR-reversing ability and mechanisms were analyzed through cytotoxicity and combination index (CI), cell cycle, and apoptosis experiments. P-gp efflux function was significantly inhibited by cinnamophilin without influencing the drug's expression or conformation. Cinnamophilin uncompetitively inhibited the efflux of doxorubicin and rhodamine 123 and exhibited a distinct binding behavior compared with verapamil, the P-gp standard inhibitor. The half maximal inhibitory concentration of cinnamophilin for doxorubicin and rhodamine 123 efflux was 12.47 and 11.59 μM, respectively. In regard to P-gp energy consumption, verapamil-stimulated ATPase activity was further enhanced by cinnamophilin at concentrations of 0.1, 1, 10, and 20 μM. In terms of MDR reversion, cinnamophilin demonstrated synergistic cytotoxic effects when combined with docetaxel, vincristine, or paclitaxel. The CI was < 0.7 in all experimental combination treatments. The present study showed that cinnamophilin possesses P-gp-modulating effects and cancer MDR resensitizing ability., (Copyright © 2021 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Verapamil, a calcium channel blocker, has been approved as the first-line drug for treatment of angina pectoris, hypertension and supraventricular tachycardia. Lactobacillus rhamnosus, one of the normal strains in human intestinal tract, is very popular in the probiotic market for conferring a health benefit on the host. This report investigated the potential of gut microbiota-drug interactions between lactobacillus rhamnosus and verapamil via using wild type (WT) and Cyp3a1/2 knockout (KO) rats. In WT rats, administration of Lactobacillus rhamnosus for 14 days decreased systemic exposure of verapamil and increased its metabolite norverapamil in vivo, and resulted in gut microbiota-drug interactions. In Cyp3a1/2 KO rats, however, this interaction disappeared. Further studies found that Lactobacillus rhamnosus induced CYP3A activity and expression, and changed the composition of gut microbiota, thus changing the pharmacokinetics of verapamil. These results demonstrated the interaction between lactobacillus rhamnosus and verapamil, and indicated that the effect of gut microbiota on metabolic enzymes cannot be ignored., Competing Interests: Declaration of Competing Interest The authors report no declarations of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A novel, fast and sensitive enantioselective HPLC assay with a new core-shell isopropyl carbamate cyclofructan 6 (superficially porous particle, SPP) chiral column (LarihcShell-P, LSP) was developed and validated for the enantiomeric separation and quantification of verapamil (VER) in rat plasma. The polar organic mobile phase composed of acetonitrile/methanol/trifluoroacetic acid/triethylamine (98:2:0.05: 0.025, v/v/v/v ) and a flow rate of 0.5 mL/min was applied. Fluorescence detection set at excitation/emission wavelengths 280/313 nm was used and the whole analysis process was within 3.5 min, which is 10-fold lower than the previous reported HPLC methods in the literature. Propranolol was selected as the internal standard. The S-(-)- and R-(+)-VER enantiomers with the IS were extracted from rat plasma by utilizing Waters Oasis HLB C18 solid phase extraction cartridges without interference from endogenous compounds. The developed assay was validated following the US-FDA guidelines over the concentration range of 1-450 ng/mL (r 2 ≥ 0.997) for each enantiomer (plasma) and the lower limit of quantification was 1 ng/mL for both isomers. The intra- and inter-day precisions were not more than 11.6% and the recoveries of S-(-)- and R-(+)-VER at all quality control levels ranged from 92.3% to 98.2%. The developed approach was successfully applied to the stereoselective pharmacokinetic study of VER enantiomers after oral administration of 10 mg/kg racemic VER to Wistar rats. It was found that S-(-)-VER established higher C max and area under the concentration-time curve (AUC) values than the R-(+)-enantiomer. The newly developed approach is the first chiral HPLC for the enantiomeric separation and quantification of verapamil utilizing a core-shell isopropyl carbamate cyclofructan 6 chiral column in rat plasma within 3.5 min after solid phase extraction (SPE).

In this study, we developed a new method for simultaneous determination of verapamil hydrochloride (VerHCl) and its metabolite norverapamil hydrochloride (NorHCl) by using the capillary electrophoresis-electrochemiluminescence. Under optimized experimental conditions, the linear ranges of the VerHCl and NorHCl concentrations were 0.015-10.0 and 0.060-10.0 μg/mL, respectively. The linearity relations were determined using the respective regression equations y = 581.2x + 19.94 and y = 339.4x + 29.16. The respective limits of detection (S/N = 3) were 0.006 and 0.024 μg/mL. The proposed method was used to study the pharmacokinetics of both agents in rat plasma. The maximum concentration (Cmax), half-life time (T1/2) and time to peak (Tmax) were 683.21 ± 74.81 ng/mL, 0.52 ± 0.21 h and 2.49 ± 0.32 h for VerHCl and 698.42 ± 71.45 ng/mL, 1.14 ± 0.26 h and 2.83 ± 0.23 h for NorHCl, respectively, following oral administration of 10 mg/kg VerHCl., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Multidrug resistance remains a huge challenge in the chemotherapy of cancer and numerous studies have reported that P-glycoprotein is the most common mechanism of multidrug resistance. Verapamil has been shown to be able to reverse development of multidrug resistance mediated by P-glycoprotein. However, the mechanism of action for verapamil in reversing multidrug resistance at the metabolic level has been rarely reported. In this research, we report the reversal effect of verapamil on multidrug resistance and its mechanisms of action using metabolomics. The results show that the P-glycoprotein-mediated chemotherapy drug resistance was significantly reversed by verapamil in resistant SW620/Ad300 cells. In-depth studies demonstrated that verapamil at reversal concentration had no effect on the P-glycoprotein expression level, but increased intramolecular accumulation of paclitaxel in SW620/Ad300 cells. Metabolomics revealed that the multidrug resistance of SW620/Ad300 cells was related to changes in glycerophospholipid metabolism, sphingolipid metabolism and citric acid cycle, and verapamil could antagonize the multidrug resistance by reversing the above-mentioned glycerophospholipid metabolism and sphingolipid metabolism. This research shows the multidrug resistance reversal mechanism of verapamil at the metabolic level, which helps in understanding the exact multidrug resistance mechanism of verapamil and might be potentially useful to find new multidrug resistance reversal agents. The combination of verapamil (VRP) and paclitaxel (PTX) yielded synergistic effects. VRP had no effect on the expression of P-gp, but increased intramolecular accumulation of PTX. VRP antagonized the MDR by regulating glycerophospholipid metabolism and sphingolipid metabolism., (© 2020 John Wiley & Sons, Ltd.)

( R )-[ 11 C]verapamil is a radiotracer widely used for the evaluation of the P-glycoprotein (P-gp) function at the blood-brain barrier (BBB). Several studies have evaluated the pharmacokinetics of ( R )-[ 11 C]verapamil in rats and humans under different conditions. However, to the best of our knowledge, the pharmacokinetics of ( R )-[ 11 C]verapamil have not yet been evaluated in nonhuman primates. Our study aims to establish ( R )-[ 11 C]verapamil as a reference P-gp tracer for comparison of a newly developed P-gp positron emission tomography (PET) tracer in a species close to humans. Therefore, the study assesses the kinetics of ( R )-[ 11 C]verapamil and evaluates the effect of scan duration and P-gp inhibition on estimated pharmacokinetic parameters. Three nonhuman primates underwent two dynamic 91 min PET scans with arterial blood sampling, one at baseline and another after inhibition of the P-gp function. The ( R )-[ 11 C]verapamil data were analyzed using 1-tissue compartment model (1-TCM) and 2-tissue compartment model fits using plasma-corrected for polar radio-metabolites or non-corrected for radio-metabolites as an input function and with various scan durations (10, 20, 30, 60, and 91 min). The preferred model was chosen according to the Akaike information criterion and the standard errors (SE %) of the estimated parameters. 1-TCM was selected as the model of choice to analyze the ( R )-[ 11 C]verapamil data at baseline and after inhibition and for all scan durations tested. The volume of distribution ( V T ) and the efflux constant k 2 estimations were affected by the evaluated scan durations, whereas the influx constant K 1 estimations remained relatively constant. After P-gp inhibition (tariquidar, 8 mg/kg), in a 91 min scan duration, the whole-brain V T increased significantly up to 208% ( p < 0.001) and K 1 up to 159% ( p < 0.001) compared with baseline scans. The k 2 values decreased significantly after P-gp inhibition in all the scan durations except for the 91 min scans. This study suggests the use of K 1 , calculated with 1-TCM and using short PET scans (10 to 30 min), as a suitable parameter to measure the P-gp function at the BBB of nonhuman primates.

Background: Omadacycline is a semisynthetic aminomethylcycline antibacterial derived from the tetracycline class. It is approved in the USA to treat adults with acute bacterial skin and skin-structure infections and community-acquired bacterial pneumonia., Objectives: This phase I, open-label study evaluated the effect of a potential drug-drug interaction of verapamil-a known P-glycoprotein (P-gp) inhibitor-with omadacycline on the pharmacokinetic profile of omadacycline in healthy adults. The safety and tolerability of omadacycline taken alone and in combination with verapamil were also evaluated., Methods: A single oral dose of 240 mg verapamil extended release (ER) was given 2 h prior to a single oral dose of 300 mg omadacycline., Results: Ten (83.3%) of the 12 participants enrolled in the study completed the study, and all enrolled participants were included in the safety and pharmacokinetic populations. An increase of 14-25% in systemic exposure to omadacycline was seen when administered following a single oral dose of 240 mg verapamil ER compared with omadacycline alone, as measured by the area under the concentration-time curve (AUC) from time 0 to 24 h after dosing (AUC 0-24 ), from time 0 to the last quantifiable concentration (AUC 0-t ), from time 0 extrapolated to infinity (AUC 0-inf ), and by maximum (peak) observed plasma concentration (C max ). Treatment-emergent adverse events were reported by one participant (nausea and headache)., Conclusions: These findings suggest that, if given with a known P-gp inhibitor, dose adjustment of oral omadacycline is not warranted based on small increases in absorption and systemic exposure. No safety signals were identified.

Orosomucoid polymorphisms influence plasma drug binding in humans; however, canine variants and their effect on drug plasma protein binding have not yet been reported. In this study, the orosomucoid gene (ORM1) was sequenced in 100 dogs to identify the most common variant and its allele frequency determined in 1,464 dogs (from 64 breeds and mixed-breed dogs). Plasma protein binding extent of amitriptyline, indinavir, verapamil, and lidocaine were evaluated by equilibrium dialysis using plasma from ORM1 genotyped dogs (n = 12). Free and total drug plasma concentrations were quantified by liquid chromatography-mass spectrometry. From the five polymorphisms identified in canine ORM1, two were nonsynonymous. The most common was c.70G>A (p.Ala24Thr) with an allele frequency of 11.2% (n = 1464). Variant allele frequencies varied by breed, reaching 74% in Shetland Sheepdogs (n = 21). Free drug fractions did not differ significantly (p > .05; Mann-Whitney U) between plasma collected from dogs with c.70AA (n = 4) and those with c.70GG (n = 8) genotypes. While c.70G>A did not affect the extent of plasma protein binding in our study, the potential biological and pharmacological implication of this newly discovered ORM1 variant in dogs should be further investigated., (© 2020 John Wiley & Sons Ltd.)

Background and Objective: A novel cocktail containing four substrates of key drug transporters was previously optimized to eliminate mutual drug-drug interactions between the probes digoxin (P-glycoprotein substrate), furosemide (organic anion transporter 1/3), metformin (organic cation transporter 2, multidrug and toxin extrusion protein 1/2-K), and rosuvastatin (organic anion transporting polypeptide 1B1/3, breast cancer resistance protein). This clinical trial investigated the effects of four commonly employed drug transporter inhibitors on cocktail drug pharmacokinetics., Methods: In a randomized open-label crossover trial in 45 healthy male subjects, treatment groups received the cocktail with or without single oral doses of rifampin, verapamil, cimetidine or probenecid. Concentrations of the probe drugs in serial plasma samples and urine fractions were measured by validated liquid chromatography-tandem mass spectrometry assays to assess systemic exposure., Results: The results were generally in accordance with known in vitro and/or clinical drug-drug interaction data. Single-dose rifampin increased rosuvastatin area under the plasma concentration-time curve up to the last quantifiable concentration (AUC 0-tz ) by 248% and maximum plasma concentration (C max ) by 1025%. Probenecid increased furosemide AUC 0-tz by 172% and C max by 23%. Cimetidine reduced metformin renal clearance by 26%. The effect of single-dose verapamil on digoxin systemic exposure was less than expected from multiple-dose studies (AUC 0-tz unaltered, C max  + 22%)., Conclusions: Taking all the interaction results together, the transporter cocktail is considered to be validated as a sensitive and specific tool for evaluating transporter-mediated drug-drug interactions in drug development., Clinical Trial Registration: EudraCT number 2017-001549-29.

Roux-en-Y gastric bypass surgery (RYGBS) is an effective surgical intervention to reduce mortality in morbidly obese patients. Following RYGBS, the disposition of drugs may be affected by anatomical alterations and changes in intestinal and hepatic drug metabolizing enzyme activity. The aim of this study was to better understand the drug-drug interaction (DDI) potential of CYP3A and P-gp inhibitors. The impacts of RYGBS on the absorption and metabolism of midazolam, acetaminophen, digoxin, and their major metabolites were simulated using physiologically-based pharmacokinetic (PBPK) modeling. PBPK models for verapamil and posaconazole were built to evaluate CYP3A- and P-gp-mediated DDIs pre- and post-RYGBS. The simulations suggest that for highly soluble drugs, such as verapamil, the predicted bioavailability was comparable pre- and post-RYGBS. For verapamil inhibition, RYGBS did not affect the fold-change of the predicted inhibited-to-control plasma AUC ratio or predicted inhibited-to-control peak plasma concentration ratio for either midazolam or digoxin. In contrast, the predicted bioavailability of posaconazole, a poorly soluble drug, decreased from 12% pre-RYGBS to 5% post-RYGBS. Compared to control, the predicted posaconazole-inhibited midazolam plasma AUC increased by 2.0-fold pre-RYGBS, but only increased by 1.6-fold post-RYGBS. A similar trend was predicted for pre- and post-RYGBS inhibited-to-control midazolam peak plasma concentration ratios (2.0- and 1.6-fold, respectively) following posaconazole inhibition. Absorption of highly soluble drugs was more rapid post-RYGBS, resulting in higher predicted midazolam peak plasma concentrations, which was further increased following inhibition by verapamil or posaconazole. To reduce the risk of a drug-drug interaction in patients post-RYGBS, the dose or frequency of object drugs may need to be decreased when administered with highly soluble inhibitor drugs, especially if toxicities are associated with plasma peak concentrations.

Objectives For revealing the peculiarities of the drug-drug interaction of rivaroxaban (substrate CYP3A4 and P-gp) and calcium channel blockers (CCBs) (verapamil - inhibitor CYP3A4 and P-gp and amlodipine - substrate CYP3A4) in patients 80 years and older with nonvalvular atrial fibrillation (NAF) we studied 128 patients. Methods All patients were divided into groups depending on the therapy taken: the 1st - rivaroxaban + amlodipine (n=51), the 2nd - rivaroxaban + verapamil (n=30), the control group - rivaroxaban without CCBs (n=47). A trough steady-state plasma concentration (C min,ss) of rivaroxaban, prothrombin time (PT) in the blood plasma and the event of clinically relevant non-major (CRNM) bleeding were assessed for each patient. Results Patient in group 2 had higher C min,ss of rivaroxaban, PT and CRNM than subjects in the control group (Me 73.8 [50.6-108.8] ng/mL vs. 40.5 [25.6-74.3] ng/mL; Me 14.8 [13.4-17.3] s vs. 13.8 [12.6-14.4] s; 34% vs. 13%, respectively, p<0.05 for all). When compared, the PT and complication rate in group 1 with the control group C min,ss of rivaroxaban were practically the same (p>0.05 for all). Conclusions In patients ≥80 years with NAF, the use of rivaroxaban in combination with verapamil may not be safe and can lead to CRNM bleeding.

Prediction of human pharmacokinetics is important in the preclinical stage. Values for total clearance of compounds from plasma should be one of the most important pharmacokinetic parameters for predictions. Although several physiological and empirical methods including single-species allometry for prediction of values for human clearance of compounds using humanized-liver mice have been reported, further improvement of prediction accuracies would be still expected. To optimize these approaches, we proposed methods for unbound intrinsic clearance in virtually 100% humanized-liver mouse by incorporating unbound plasma fractions of compounds in differently humanized-liver mice. Comparisons of prediction accuracies of values for human clearance of 15 model compounds were performed among our current physiological and previously reported models and single-species allometry using humanized-liver mice. Incorporation of the actual unbound plasma fractions of compounds and correction of residual mice hepatocyte in humanized-liver mice showed comparable prediction accuracy to that by single-species allometry. After exclusion of 3 compounds with large species differences in values of clearance and unbound plasma fractions between mice and humans out of 15 compounds, prediction accuracies were improved in the methods investigated. The previously and present reported physiological methods could show the good prediction accuracy of values for clearance of drugs from plasma., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2020 The Japanese Society for the Study of Xenobiotics. Published by Elsevier Ltd. All rights reserved.)

Abemaciclib, a selective inhibitor of cyclin-dependent kinases 4 and 6, is metabolized mainly by cytochrome P450 (CYP)3A4. Clinical studies were performed to assess the impact of strong inhibitor (clarithromycin) and inducer (rifampin) on the exposure of abemaciclib and active metabolites. A physiologically based pharmacokinetic (PBPK) model incorporating the metabolites was developed to predict the effect of other strong and moderate CYP3A4 inhibitors and inducers. Clarithromycin increased the area under the plasma concentration-time curve (AUC) of abemaciclib and potency-adjusted unbound active species 3.4-fold and 2.5-fold, respectively. Rifampin decreased corresponding exposures 95% and 77%, respectively. These changes influenced the fraction metabolized via CYP3A4 in the model. An absolute bioavailability study informed the hepatic and gastric availability. In vitro data and a human radiolabel study determined the fraction and rate of formation of the active metabolites as well as absorption-related parameters. The predicted AUC ratios of potency-adjusted unbound active species with rifampin and clarithromycin were within 0.7- and 1.25-fold of those observed. The PBPK model predicted 3.78- and 7.15-fold increases in the AUC of the potency-adjusted unbound active species with strong CYP3A4 inhibitors itraconazole and ketoconazole, respectively; and 1.62- and 2.37-fold increases with the concomitant use of moderate CYP3A4 inhibitors verapamil and diltiazem, respectively. The model predicted modafinil, bosentan, and efavirenz would decrease the AUC of the potency-adjusted unbound active species by 29%, 42%, and 52%, respectively. The current PBPK model, which considers changes in unbound potency-adjusted active species, can be used to inform dosing recommendations when abemaciclib is coadministered with CYP3A4 perpetrators., (© 2020 Eli Lilly and Company. The Journal of Clinical Pharmacology published by Wiley Periodicals, Inc. on behalf of American College of Clinical Pharmacolog.)

Paclitaxel is the backbone of standard chemotherapeutic regimens used in a number of malignancies and is frequently given with concomitant medications. Newly developed oncolytic agents, including tyrosine kinase inhibitors are often shown to be CYP3A4 and P-gp inhibitors. The aim of this study was to develop a PBPK model for intravenously administered paclitaxel in order to predict the incidence of neutropenia and to estimate the DDI potential as a victim drug. The dose-dependent effects on paclitaxel plasma protein binding, volume of distribution and drug clearance were considered for dose levels of 80 mg/m 2 , 135 mg/m 2 and 175 mg/m 2 . A pharmacodynamics model that incorporate the impact of paclitaxel on the neutrophil was developed. The relative metabolic clearance via CYP3A4 and CYP2C8, the renal clearance as well as P-gp mediated biliary clearance were incorporated in the model in order to assess the neutropenia in the presence of DDI. The developed PBPK-PD model was able to recover the drop in neutrophils observed after the administration of 175mg/m2 of paclitaxel over a 3-h duration. The mean nadir observed was 1.9 × 10 9 neutrophils/L and was attained after 10 days of treatment, and a fraction of 47% of the population was predicted to have at some point a neutropenia including 12% with severe neutropenia. In the case of concomitant administration of ketoconazole, 39% of the population was predicted to suffer from severe neutropenia. In summary, PBPK-PD modeling allows a priori prediction of DDIs and safety events involving complex combination therapies which are often utilized in an oncology setting., Competing Interests: Declaration of Competing Interest All of the authors are employees of Certara UK Limited., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this study, UC rat model was established by administration of 5% (w/v) dextran sulfate sodium, and the pharmacokinetics of verapamil and norverapamil were evaluated in normal and UC rats using UPLC-MS/MS after oral administration of 5 mg/kg and 50 mg/kg verapamil.The peak concentration (C max ) and the area under plasma concentration-time curves (AUC) of verapamil in UC rats after oral administration of 5 mg/kg were significantly greater (2.5 times and 2 times, respectively) than those in normal rats, but the clearance rate (Cl) was significantly lower (by 50%). For norverapamil, C max and AUC were significantly greater (2.8 times and 2.5 times, respectively), and Cl was significantly lower (by 45%). But, pharmacokinetic parameters of verapamil and norverapamil after oral administration of 50 mg/kg were no significant differences between UC and normal rats.The better absorption and poor excretion for low-dose verapamil may be attributed to down-regulation of P-gp expression in the intestine and kidney. No significant differences of pharmacokinetic parameters for high-dose verapamil may be explained as the saturation of an efflux mechanism.The findings of this study suggested that in UC patients, doses of verapamil should be decreased when low-dose verapamil was orally administrated.

Objectives: To investigate effects of short-chain fatty acids (SCFAs) on expressions and functions of intestinal cytochrome P4503A (Cyp3a) and P-glycoprotein (P-gp). To develop a semi-physiologically based pharmacokinetic (semi-PBPK) model for assessing their contributions., Methods: Verapamil pharmacokinetics was investigated following oral administration to rats receiving water containing 150 mm SCFAs for 3 weeks. Cyp3a activities in intestinal and liver mircosomes were assessed by norverapamil formation. In-situ single-pass perfusion was used to evaluate intestinal transport of verapamil and P-gp function. Functions and expressions of Cyp3a and P-gp were measured in mouse primary enterocytes following 48-h exposure to SCFAs. Contributions of intestinal P-gp and Cyp3a to verapamil pharmacokinetics were assessed using a semi-PBPK model., Key Findings: Short-chain fatty acids significantly increased oral plasma exposures of verapamil and norverapamil. SCFAs upregulated Cyp3a activity and expression, but downregulated P-gp function and expression in rat intestine, which were repeated in mouse primary enterocytes. PBPK simulation demonstrated contribution of intestinal Cyp3a to oral plasma verapamil exposure was minor, and the increased oral plasma verapamil exposure was mainly attributed to downregulation of intestinal P-gp., Conclusions: Short-chain fatty acids oppositely regulated functions and expressions of intestinal Cyp3a and P-gp. The downregulation of P-gp mainly contributed to the increased oral plasma verapamil exposure by SCFAs., (© 2019 Royal Pharmaceutical Society.)

In oral bioavailability studies, evaluation of the absorption and transport of drugs and food components across the intestinal barrier is crucial. Advances in the field of organ-on-a-chip technology have resulted in a dynamic gut-on-a-chip model that better mimics the in vivo microenvironment of the intestine. Despite a few recent integration attempts, ensuring a biologically relevant microenvironment while coupling with a fully online detection system still represents a major challenge. Herein, we designed an online technique to measure drug permeability and analyse unknown product formation across an intestinal epithelial layer of Caco-2 and HT29-MTX cells cultured on a flow-through Transwell system, while ensuring the quality and relevance of the biological model. Chip-based ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) was coupled to the dynamic Transwell system via a series of switching valves, thus allowing alternating measurements of the apical and basolateral sides of the in vitro model. Two trap columns were integrated for online sample pre-treatment and compatibility enhancement. Temporal analysis of the intestinal permeability was successfully demonstrated using verapamil as a model drug and ergotamine epimers as a model for natural toxins present in foods. Evidence was obtained that our newly developed dynamic system provided reliable results versus classical static in vitro models, and moreover, for the first time, epimer-specific transport is shown for ergotamine. Finally, initial experiments with the drug granisetron suggest that metabolic activity can be studied as well, thus highlighting the versatility of the bio-integrated online analysis system developed. Graphical abstract.

We studied pharmacokinetics and bioavailability of verapamil, propranolol, and ethacizine in healthy volunteers after single oral administration under normal conditions and on the second day of simulated antiorthostatic hypokinesia modeling some effects of microgravity. Under conditions of antiorthostatic hypokinesia, a tendency to a decrease in half-elimination period, mean retention time, and volume of distribution and an increase in the rate of absorption, ratio of maximum concentrations, and relative rate of absorption of verapamil and propranolol were revealed. For ethacizine, a statistically significant increase in the time of attaining maximum concentration and volume of distribution and a decrease in the maximum concentration, rate of absorption, ratio of maximum concentrations, and relative rate of absorption under conditions of antiorthostatic hypokinesia were found.

Polymeric micelles (PMs) are currently under investigation as potential nanocarriers for oral administration of paclitaxel (PTX). Previously, we developed amphiphilic carboxymethyl chitosan-rhein (CR) conjugate for oral delivery of PTX. PTX-loaded CR PMs exhibited a homogeneous and small size (<200 nm) with a drug loading capacity (DL) of 35.46 ± 1.07%. However, The absorption parameters of PTX using CR PMs have not been studied before. Here, we evaluated the intestinal permeation of CR PMs by in situ intestinal absorption experiments. PTX-loaded CR PMs enhanced the absorption of PTX in the intestine without causing significant intestinal villi injury. Compared to the P-glycoprotein (P-gp) inhibition of verapamil, the transport mechanism of CR PMs across intestinal epithelial cells may bypass P-gp efflux. Caco-2 cell uptake assays also confirmed that CR PMs can be taken up into the enterocyte as whole and independent of P-gp. Local biodistribution evaluation showed that fluorescence-labeled CR PMs were absorbed into the intestinal villi. In vivo bioimaging of tumor-bearing mice verified a significant portion of CR PMs were intactly absorbed through the intestine, then distributed and accumulated at the tumor site. For their significant intestinal permeation enhancement, CR PMs might be considered as promising oral delivery carriers for PTX and other water-insoluble drugs., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Rivaroxaban is indicated for stroke prevention in nonvalvular atrial fibrillation (AF). Its elimination is mediated by both hepatic metabolism and renal excretion. Consequently, its clearance is susceptible to both intrinsic (pathophysiological) and extrinsic (concomitant drugs) variabilities that in turn implicate bleeding risks. Upon systematic model verification, physiologically based pharmacokinetic (PBPK) models are qualified for the quantitative rationalization of complex drug-drug-disease interactions (DDDIs). Hence, this study aimed to develop and verify a PBPK model of rivaroxaban systematically. Key parameters required to define rivaroxaban's disposition were either obtained from in vivo data or generated via in vitro metabolism and transport kinetic assays. Our developed PBPK model successfully predicted rivaroxaban's clinical pharmacokinetic parameters within predefined success metrics. Consideration of basolateral organic anion transporter 3 (OAT3)-mediated proximal tubular uptake in tandem with apical P-glycoprotein (P-gp)-mediated efflux facilitated mechanistic characterization of the renal elimination of rivaroxaban in both healthy and renal impaired patients. Retrospective drug-drug interaction (DDI) simulations, incorporating in vitro metabolic inhibitory parameters, accurately recapitulated clinically observed attenuation of rivaroxaban's hepatic clearance due to enzyme-mediated DDIs with CYP3A4/2J2 inhibitors (verapamil and ketoconazole). Notably, transporter-mediated DDI simulations between rivaroxaban and the P-gp inhibitor ketoconazole yielded minimal increases in rivaroxaban's systemic exposure when P-gp-mediated efflux was solely inhibited, but were successfully characterized when concomitant basolateral uptake inhibition was incorporated in the simulation. In conclusion, our developed PBPK model of rivaroxaban is systematically verified for prospective interrogation and management of untested yet clinically relevant DDDIs pertinent to AF management using rivaroxaban. SIGNIFICANCE STATEMENT: Rivaroxaban is susceptible to DDDIs comprising renal impairment and P-gp and CYP3A4/2J2 inhibition. Here, systematic construction and verification of a PBPK model of rivaroxaban, with the inclusion of a mechanistic kidney component, provided insight into the previously arcane role of OAT3-mediated basolateral uptake in influencing both clinically observed renal elimination of rivaroxaban and differential extents of transporter-mediated DDIs. The verified model holds potential for investigating clinically relevant DDDIs involving rivaroxaban and designing dosing adjustments to optimize its pharmacotherapy in atrial fibrillation., (Copyright © 2019 by The American Society for Pharmacology and Experimental Therapeutics.)

Tozadenant is one of the selective adenosine A2a receptor antagonists with a potential to be a new Parkinson's disease (PD) therapeutic drug. In this study, a liquid chromatography-mass spectrometry based bioanalytical method was qualified and applied for the quantitative analysis of tozadenant in rat plasma. A good calibration curve was observed in the range from 1.01 to 2200 ng/mL for tozadenant using a quadratic regression. In vitro and preclinical in vivo pharmacokinetic (PK) properties of tozadenant were studied through the developed bioanalytical methods, and human PK profiles were predicted using physiologically based pharmacokinetic (PBPK) modeling based on these values. The PBPK model was initially optimized using in vitro and in vivo PK data obtained by intravenous administration at a dose of 1 mg/kg in rats. Other in vivo PK data in rats were used to validate the PBPK model. The human PK of tozadenant after oral administration at a dose of 240 mg was simulated by using an optimized and validated PBPK model. The predicted human PK parameters and profiles were similar to the observed clinical data. As a result, optimized PBPK model could reasonably predict the PK in human.

Objective: Extended release (ER) tablets/capsules in massive ingestion overdoses are prone to form pharmacobezoars potentially increasing the risk of late-appearing toxic effects and prolonged symptoms. Oral activated charcoal is often sufficient to prevent drug absorption, but in a recent massive ingestion of highly toxic substances, prior orogastric lavage might be considered. The disintegration characteristics of ER preparations in overdose situations is valuable to understand if the time line and course of the intoxication might be prolonged, but information on these characteristics are unavailable. Slow disintegration and/or pharmacobezoar formation, and the large size makes ER preparation impossible to evacuate using a 30F orogastric lavage tube. This study evaluates the disintegration and pharmacobezoar formation of a simulated massive ER tablet ingestion in an in vitro model, using a selection of extended release tablets, with different disintegrating characteristics when present in therapeutic numbers. Furthermore, the sizes of the formed pharmacobezoars were compared with the dimensions of a 30F orogastric lavage tube., Method: A standardized model mimicking the physical effects on pharmaceutical preparations in simulated gastric fluid (SGF) was developed and tested on three mono-depot ER tablets (quetiapine/Seroquel ® XR 50 mg, paracetamol/Pinex ® Retard 500 mg, verapamil/Isoptin ® Retard 240 mg), one poly-depot ER tablet (carbamazepine/Tegretol ® Retard 200 mg), and one immediate-release tablet (paracetamol/Panodil ® 500mg). Thirty tablets were placed in polyamide mesh bags, either together in one bag or in separate bags, immersed in 1 L SGF, and incubated at 37 °C for 48 h. Released drugs were quantified at 0.5-48 h., Results: Visual inspection showed that Seroquel ® XR, Pinex ® Retard, and Isoptin ® Retard tablets formed firm pharmacobezoars stable for more than 4 h and intact fractions remained for up to 24 h. Drug releases were reduced by 53%, 40%, and 31%, respectively, for up to 8 h compared to separated tablets. Light microscopy showed that contact with SGF transformed the coating of Seroquel ® XR and Pinex ® Retard to a diffusion-controlled swelled gel-layer, and the Isoptin ® Retard tablets into a rigid and slow-releasing matrix. Tegretol ® Retard disintegrated into microspheres within 30 min, and Panodil ® disintegrated within minutes., Discussion: The developed pharmacobezoars of mono-depot ER tablets demonstrated prolonged drug release. Neither the formed pharmacobezoars, nor the single tablets of the tested mono-depot ER preparations, would pass through the lumen of a standard orogastric lavage tube, rendering this modality ineffective for tablet removal in gastrointestinal decontamination.

Herein, we describe a novel amphipathic chitosan derivative (N-octyl-N'-phthalyl-O-phosphoryl chitosan, abbreviated as OPPC) as an effective oral delivery platform for P-gp substrates, especially paclitaxel (PTX). OPPC could readily self-assemble into micelles, solubilize and encapsulate PTX into the hydrophobic inner core of OPPC with superior loading capacity to chitosan. PTX/OPPC micelles possessed improved intestinal epithelial permeability and oral bioavailability of PTX evaluated by in situ perfusion and pharmacokinetic studies. In vivo fluorescence imaging revealed enhanced stability and integrity of OPPC micelles in mice gastrointestine. Furthermore, cellular uptake studies revealed effective transport and accumulation of OPPC micelles loading PTX or rhodamine-123 into Caco-2 cells via clathrin/cavelin-mediated endocytosis and OPPC-mediated P-gp inhibition. Mechanistically, the inhibition of P-gp efflux pumps by OPPC resulted from the reduction of membrane fluidity and decreased P-gp ATPase activity. In summary, OPPC micelles may serve as an efficient and promising delivery system for enhancing oral bioavailability of P-gp substrates., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Plasma concentrations of dabigatran, an active principle of prodrug dabigatran etexilate (DABE), are increased by renal impairment (RI) or coadministration of a P-glycoprotein inhibitor. Because the combined effects of drug-drug interactions and RI have not been evaluated by means of clinical studies, the decision of DABE dosing for RI patients receiving P-glycoprotein inhibitors is empirical at its best. We conducted virtual drug-drug interactions studies between DABE and the P-glycoprotein inhibitor verapamil in RI populations using physiologically based pharmacokinetic modeling. The developed physiologically based pharmacokinetic model for DABE and dabigatran was used to predict trough dabigatran concentrations in the presence and absence of verapamil in virtual RI populations. The population-based physiologically based pharmacokinetic model provided the most appropriate dosing regimen of DABE for likely clinical scenarios, such as drug-drug interactions in this RI population based on available knowledge of the systems changes and in the absence of actual clinical studies., (© 2019 The Authors CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals, Inc. on behalf of the American Society for Clinical Pharmacology and Therapeutics.)

Background: Clinical development of lesinurad, a selective uric acid reabsorption inhibitor, required analysis of lesinurad in plasma from special patient populations., Methods: EMA and FDA bioanalytical method validation guidance have recommended studying matrix effects on quantitation if samples from special patient populations are to be analyzed. In addition to lesinurad (plasma protein binding 98.2%), the matrix effects from special population plasma on the quantitation of verapamil (PPB 89.6%), allopurinol and oxypurinol (PPB negligible) were also investigated., Results: The plasma from special population patients had no matrix effects on the three quantification methods with stable isotope labeled internal standard, protein precipitation extraction, and LC-MS/MS detection. The validated lesinurad plasma quantification method was successfully applied for the pharmacokinetic evaluations to support the clinical studies in renal impaired patients., Conclusion: Special population plasma did not affect quantitation of drugs with a wide range of plasma protein binding levels in human plasma. With the confirmation that there is no impact on quantification from the matrix, the bioanalytical method can be used to support the pharmacokinetic evaluations for clinical studies in special populations., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Purpose: Ovarian cancer is usually treated with transurethral resection or systemic chemotherapy in clinic. However, the development of drug resistance in ovarian cancer is frequently observed in ovarian cancer patients, leading to failure of tumor inhibition and recurrence. In this study, we aimed to efficiently reverse the drug resistance and enhance the anticancer effects by co-delivery of chemotherapeutic agents and multi-drugs resistant proteins inhibitor in ovarian cancer treatment., Methods: The cell viability was measured by using MTT or flow cytometry (Annexin V/PI staining) under different culture conditions. Western blot was used to detect the expression of P-gp. We employed confocol to visualize the drug distribution under different culture systems. Using flow cytometry, we examined the drug absorption. MPEG-PLA was used to load chemotherapeutic drugs. We also applied mice model to evaluate the killing ability and side effects of free or methoxy poly (ethylene glycol)-poly (l-lactic acid) (MPEG-PLA) loaded drugs., Results: We found that pre-treatment of verapamil, a multi-drugs resistant proteins inhibitor, could efficiently reverse the drug resistant in ovarian cancer. To further improve the pharmacokinetics profiles and avoid the systemic toxicity caused by agents, we encapsulated verapamil and doxorubicin (DOX) by polymeric nanoparticles MPEG-PLA. Co-delivery of verapamil and DOX by nano-carrier revealed reduced drug resistance and enhanced anticancer effects compared with the free drug delivery. More importantly, accumulated drugs, prolonged drug circulation and reduced systemic were observed in nanoparticles encapsulation group., Conclusion: Co-delivery of verapamil and chemotherapeutic drugs by MPEG-PLA efficiently reversed the drug resistance, resulting in enhanced anticancer effects along with reduced systemic toxicity, which provides potential clinical applications for drug resistant ovarian cancer treatment., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

1. This study investigates the effects of verapamil on the pharmacokinetics of dihydromyricetin in rats and clarifies its main mechanism. 2. The pharmacokinetic profiles of oral or intravenous administration of dihydromyricetin in Sprague-Dawley rats with or without pretreatment with verapamil were investigated. In addition, the effects of verapamil on the transport and metabolic stability of dihydromyricetin were investigated using Caco-2 cell transwell model and rat liver microsomes. 3. In the oral group, verapamil could significantly increase C max , and decrease oral clearance of dihydromyricetin (p < 0.05). In the intravenous group, the C max also increased compared with the control group, but the difference was not significant. However, the t 1/2 and clearance rate decreased than that of the control (p < 0.05). The oral bioavailability increased significantly (p < 0.05) from 3.84% to 6.84% with the pretreatment of verapamil. A markedly higher transport of dihydromyricetin across the Caco-2 cells was observed in the basolateral-to-apical direction and was abrogated in the presence of the P-gp inhibitor, verapamil. Additionally, the intrinsic clearance rate of dihydromyricetin was decreased by the pretreatment with verapamil (27.0 versus 32.5 μL/min/mg protein). 4. Those results indicated that verapamil could significantly change the pharmacokinetic profiles of dihydromyricetin in rats, and it might exert these effects through increasing the absorption of dihydromyricetin by inhibiting the activity of P-gp, or through inhibiting the metabolism of dihydromyricetin in rat liver.

Pharmacokinetics and antithrombotic effects of the Factor Xa inhibitor rivaroxaban were studied in subjects with mild renal insufficiency concurrently taking the P-glycoprotein and moderate CYP3A inhibitor verapamil, a drug commonly administered to patients with hypertension, ischemic heart disease, or atrial fibrillation. Age-matched controls with normal renal function were studied concurrently. Subjects' overall mean age was 59 years. Mean creatinine clearance values in the 2 groups were 105 and 71 mL/min. After single 20-mg oral doses, rivaroxaban area under the curve (AUC) was increased by a factor of 1.11 (ratio of geometric means [RGM]) in mild renal insufficiency compared to controls. Verapamil coadministration independently increased AUC to the same extent in both the mild renal insufficiency and control groups (RGM, 1.39 and 1.43). Concurrent mild renal insufficiency and verapamil produced additive inhibition compared to controls without verapamil (RGM, 1.58). Prothrombin time (PT) prolongation and Factor Xa inhibition tracked plasma rivaroxaban, and were enhanced by verapamil. Concentration-response relationships for PT (linear) and Factor Xa inhibition (hyperbolic) were unaffected by renal function or verapamil. The absolute and relative increases in rivaroxaban AUC caused by verapamil in mild renal insufficiency subjects are potentially associated with an increased bleeding risk. Modification of recommended dosage may be required in this combination of circumstances to reduce risk to patients., (© 2017, The American College of Clinical Pharmacology.)

Purpose: To investigate the blood-to-retina verapamil transport at the blood-retinal barrier (BRB)., Methods: EverFluor FL Verapamil (EFV) was adopted as the fluorescent probe of verapamil, and its transport across the BRB was investigated with common carotid artery infusion in rats. EFV transport at the inner and outer BRB was investigated with TR-iBRB2 cells and RPE-J cells, respectively., Results: The signal of EFV was detected in the retinal tissue during the weak signal of cell impermeable compound. In TR-iBRB2 cells, the localization of EFV differed from that of LysoTracker ® Red, a lysosomotropic agent, and was not altered by acute treatment with NH 4 Cl. In RPE-J cells, the punctate distribution of EFV was partially observed, and this was reduced by acute treatment with NH 4 Cl. EFV uptake by TR-iBRB2 cells was temperature-dependent and membrane potential- and pH-independent, and was significantly reduced by NH 4 Cl treatment during no significant effect obtained by different extracellular pH and V-ATPase inhibitor. The EFV uptake by TR-iBRB2 cells was inhibited by cationic drugs, and inhibited by verapamil in a concentration-dependent manner with an IC 50 of 98.0 μM., Conclusions: Our findings provide visual evidence to support the significance of carrier-mediated transport in the blood-to-retina verapamil transport at the BRB.

Flavonoids are a large group of polyphenols and widely distributed in plant foods. Flavonoids exhibit various biological activities, such as anti-cancer, antioxidant and anti-inflammatory while poor oral bioavailability has been considered as a major hurdle in their use as functional foods. Cellular uptake and efflux of flavonoid implicates their bioavailability. To investigate the cellular uptake and efflux of flavonoids, 27 flavonoids were measured for their cellular uptake in Caco-2 cells with (CUV) and without (CU) the inhibitor of P-glycoprotein (P-gp) verapamil. Then, a quantitative structure-absorption relationship (QSAR) model containing 21 compounds as training set was obtained from their corresponding CU. The model showed good robustness and predictivity with a high cross-validation coefficient (Q 2 ) value of 0.809 and Log of the octanol/water partition coefficient (SlogP) and atomic charge on carbon 5 (Q C5 ) were related to flavonoid uptake. The CUV of some flavonoids were significantly (p<0.05 or p<0.01) higher than their CU, suggesting that specific flavonoids are pumped out by P-gp. The structure-affinity relationship of flavonoids as substrates of P-gp was determined with the presence of 4'-OCH 3 , 3'-OCH 3 and the absence of 3'-OH, 3-OH and 4'-OH favorable for the affinity of flavonoids. These results provide valuable information for screening flavonoids with good absorption and low affinity with transporters., (Copyright © 2017. Published by Elsevier Ltd.)

The purpose of this study was to establish physiologically based pharmacokinetic models to predict in humans the brain concentration-time profiles and P-glycoprotein (Pgp)-mediated brain drug-drug interactions between the model Pgp substrate (R)-[ 11 C]verapamil (VPM), the model dual Pgp/breast cancer resistance protein (BCRP) substrate [ 11 C]tariquidar (TQD), and the Pgp inhibitor tariquidar. The model predictions were validated with results from positron emission tomography studies in humans. Using these physiologically based pharmacokinetic models, the differences between predicted and observed areas under the concentration-time curves (AUC) of VPM and TQD in the brain were within a 1.2-fold and 2.5-fold range, respectively. Also, brain AUC increases of VPM and TQD after Pgp inhibitor administration were predicted with 2.5-fold accuracy when in vitro inhibition constant or half-maximum inhibitory concentration values of tariquidar were used. The predicted rank order of the magnitude of AUC increases reflected the results of the clinical positron emission tomography studies. Our results suggest that the established models can predict brain exposure from the respective blood concentration-time profiles and rank the magnitude of the Pgp-mediated brain drug-drug interaction potential for both Pgp and Pgp/BCRP substrates in humans., (Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.)

Aims: The efflux transporter P-glycoprotein (ABCB1) acts at the blood-brain barrier (BBB) to restrict the distribution of many different drugs from blood to the brain. Previous data suggest an age-associated decrease in the expression and function of ABCB1 at the BBB. In the present study, we investigated the influence of age on the magnitude of an ABCB1-mediated drug-drug interaction (DDI) at the BBB., Methods: We performed positron emission tomography scans using the model ABCB1 substrate (R)-[ 11 C]verapamil in five young [26 ± 1 years, (mean ± standard deviation)] and five elderly (68 ± 6 years) healthy male volunteers before and after intravenous administration of a low dose of the ABCB1 inhibitor tariquidar (3 mg kg -1 )., Results: In baseline scans, the total distribution volume (V T ) of (R)-[ 11 C]verapamil in whole-brain grey matter was not significantly different between the elderly (V T  = 0.78 ± 0.15) and young (V T  = 0.79 ± 0.10) group. After partial (incomplete) ABCB1 inhibition, V T values were significantly higher (P = 0.040) in the elderly (V T  = 1.08 ± 0.15) than in the young (V T  = 0.80 ± 0.18) group. The percentage increase in (R)-[ 11 C]verapamil V T following partial ABCB1 inhibition was significantly greater (P = 0.032) in elderly (+40 ± 17%) than in young (+2 ± 17%) volunteers. Tariquidar plasma concentrations were not significantly different between the young (786 ± 178 nmol l -1 ) and elderly (1116 ± 347 nmol l -1 ) group., Conclusions: Our results provide the first direct evidence of an increased risk for ABCB1-mediated DDIs at the BBB in elderly persons, which may have important consequences for pharmacotherapy of the elderly., (© 2017 The British Pharmacological Society.)

To validate in situ rats intestinal single pass perfusion model based on P-glycoprotein (P-gp). Firstly, phenol red perfusion was carried out to verify the close connection structure of intestinal epithelial cells, and the integrity of the intestinal epithelium, with a gravimetric method for correcting water flux. The level of phenol red was determined by high performance liquid chromatography (HPLC) both before and after perfusion. Secondly, the positive drug digoxin specified by FDA was used to validate the model. After different mass concentrations of verapamil were given in the rats, the absorption parameters of digoxin in ileum of rats were observed and compared. The results showed that the phenol red was absorbed in rats ileum segment, with an effective permeability coefficient of (1.09±0.62)×10 ⁻⁶ cm•s ⁻¹. The experiment results indicated that the close connection structure of intestinal epithelial cells was normal, and the integrity of the intestinal epithelium was maintained well. In digoxin perfusion experiment, in case no verapamil was given, digoxin showed certain degree of absorption in rat ileum, with an effective permeability coefficient (Peff) of (1.07±0.59)×10 ⁻⁵ cm•s ⁻¹; after mass concentrations of 0.01,0.1 mmol•L ⁻¹ verapamil were given, the absorption of digoxin was on the rise in rat ileum, with an effective permeability coefficient Peff of (1.58±0.69)×10 ⁻⁵, (3.28±0.95)×10 ⁻⁵ cm•s ⁻¹ respectively (P<0.05). Digoxin perfusion experiment verified that P-gp expression in small intestine epithelium was intact and can be used in the research of P-gp efflux transporter., Competing Interests: The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose., (Copyright© by the Chinese Pharmaceutical Association.)

Context: Clarifying the potential mechanism of the poor oral bioavailability of curculigoside would be helpful for for investigating pharmacological effects and clinical applications., Objective: To clarify the main mechanism for poor oral bioavailability., Materials and Methods: First, the pharmacokinetics of curculigoside (20 mg/kg) in rats with and without pretreatment with verapamil (10 mg/kg) was determined using a sensitive and reliable LC-MS method. Then the effects of verapamil on the transport and metabolic stability of curculigoside were investigated using Caco-2 cell transwell model and rat liver microsome incubation systems., Results: The results showed that verapamil could significantly increase the peak plasma concentration (from 60.17 ng/mL to 93.66 ng/mL) and AUC 0-t (from 289.57 to 764.02 ng·h/mL) of curculigoside. The Caco-2 cell experiments indicated that the efflux ratio of curculigoside was 3.92 (P appAB 6.43 ± 0.57 × 10  -7  cm/s; P appBA 2.52 ± 0.37 × 10  -36  cm/s), P-gp might be involved in the transport of curculigoside, and verapamil could inhibit the efflux of curculigoside and increase the absorption of curculigoside significantly in the Caco-2 cell monolayer. Additionally, the rat liver microsome incubation experiments indicated that verapamil could significantly decrease the intrinsic clearance rate of curculigoside (from 38.8 to 23.6 μL/min/mg protein)., Discussion and Conclusion: These results indicated that verapamil could significantly change the pharmacokinetic profiles of curculigoside in rats, the poor absorption due to P-gp mediated efflux in intestine and high intrinsic clearance rate in rat liver may be the main reason for the poor oral absolute bioavailability of curculigoside.

The purpose of the present study is to demonstrate a useful approach (isotope-IV method) for analyzing drug-drug interactions (DDIs) following the oral administration of drugs using stable isotope-labeled compounds. Verapamil hydrochloride (VER) was used as a drug model. Deuterium-labeled VER (VER-d6, 0.005 mg/kg) was intravenously administered to rats with or without a pre-treatment with 1-aminobenzotriazole (ABT, 100 mg/kg), a potent CYP inhibitor, 1.5 h after the oral administration of VER (1 mg/kg). PK parameters such as AUC po , AUC iv , and CL tot were evaluated after the oral and intravenous administration of VER from the plasma concentration-time profiles of VER and VER-d6 in each rat. The oral bioavailability (F) of VER in rats was calculated as 0.02 ± 0.01 and was significantly increased to 0.45 ± 0.24 by the pre-treatment with ABT. Further PK analyses revealed that CYP-mediated metabolism was more strongly inhibited by ABT in the intestine (Fg) than in the liver (Fh). These results were consistent with those obtained using the conventional method in which oral and intravenous administration studies were performed using different rat groups. Therefore, the isotope-IV method is effective for performing PK analyses including DDIs after the oral administration of drugs., (Copyright © 2016 The Japanese Society for the Study of Xenobiotics. Published by Elsevier Ltd. All rights reserved.)

The creation of composite systems has become an emerging field in drug delivery. Chitosan has demonstrated several pharmaceutical advantages, especially in intranasal delivery. In this manuscript, a comparative study was conducted between regular vesicles (transfersomes and penetration enhancer vesicles) and composite vesicles (chitosan containing transfersomes and penetration enhancer vesicles) loaded with a model antihypertensive drug; verapamil hydrochloride VRP. Composite vesicles displayed larger particle size than regular vesicles owing to the coating potential of chitosan on the vesicular bilayer as displayed by transmission electron microscopy, with an increased viscosity of composite vesicles and a shift in the zeta potential values from negative to positive. The entrapment efficiency of VRP in the vesicles ranged from 24 to 64%, with best physical stability displayed with transfersomal vesicles prepared using sodium deoxycholate. Chitosan slowed the in vitro release of VRP from the selected formulation but managed to achieve high penetrability across sheep nasal mucosa as displayed by confocal laser microscopy. The chitosan composite transfersomal formulation exhibited absolute bioavailability of 81.83% compared to the oral solution which displayed only 13.04%. Findings of this manuscript highly recommend chitosan as a promising functional additive in vesicular formulations to improve the intranasal delivery of drugs with low oral bioavailability., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The Tixel is a novel device based on a thermo-mechanical ablation technology that combines a sophisticated motion and a temperature control. The fractional technology is used to transfer a very precise thermal energy to the skin thereby creating an array of microchannels, accompanying by no signs of pain or inconvenience. This study aimed to evaluate the effect of the Tixel on the skin permeability of three hydrophilic molecular models: verapamil hydrochloride, diclofenac sodium, and magnesium ascorbyl phosphate. Tixel's gold-platted stainless steel tip heated to a temperature of 400°C was applied on skin for 8ms or 9ms at a protrusion of 400μm (the distance in which the tip protrudes beyond the distance gauge). The experiments were carried out partly in vivo in humans using a fluorescent dye and a confocal microscopy and partly in vitro using porcine skin and a Franz diffusion cell system. The results obtained in this study have shown that (a) no significant collateral damage to the skin tissue and no necrosis or dermal coagulation have been noted, (b) the microchannels remained open and endured for at least 6h, and (c) the skin permeability of hydrophilic molecules, which poorly penetrate the lipophilic stratum corneum barrier, was significantly enhanced by using Tixel's pretreatment., (Copyright © 2016 Elsevier B.V. All rights reserved.)

ABCB1 and ABCG2 work together at the blood-brain barrier (BBB) to limit brain distribution of dual ABCB1/ABCG2 substrates. In this pilot study we used positron emission tomography (PET) to assess brain distribution of two model ABCB1/ABCG2 substrates ([(11) C]elacridar and [(11) C]tariquidar) in healthy subjects without (c.421CC) or with (c.421CA) the ABCG2 single-nucleotide polymorphism (SNP) c.421C>A. Subjects underwent PET scans under conditions when ABCB1 and ABCG2 were functional and during ABCB1 inhibition with high-dose tariquidar. In contrast to the ABCB1-selective substrate (R)-[(11) C]verapamil, [(11) C]elacridar and [(11) C]tariquidar showed only moderate increases in brain distribution during ABCB1 inhibition. This provides evidence for a functional interplay between ABCB1 and ABCG2 at the human BBB and suggests that both ABCB1 and ABCG2 need to be inhibited to achieve substantial increases in brain distribution of dual ABCB1/ABCG2 substrates. During ABCB1 inhibition c.421CA subjects had significantly higher increases in [(11) C]tariquidar brain distribution than c.421CC subjects, pointing to impaired cerebral ABCG2 function., (© 2016, The Authors. Clinical Pharmacology & Therapeutics published by Wiley Periodicals, Inc. on behalf of American Society for Clinical Pharmacology and Therapeutics.)

The purpose of this study was to investigate whether a pharmacokinetic model integrating in vitro mdr1a efflux activity (which we previously reported) with in vitro/in vivo differences in protein expression level can reconstruct intestinal mdr1a function. In situ intestinal permeability-surface area product ratio between wild-type and mdr1a/1b (-/-) mice is one of the parameters used to describe intestinal mdr1a function. The reconstructed ratios of six mdr1a substrates (dexamethasone, digoxin, loperamide, quinidine, verapamil, vinblastine) and one nonsubstrate (diazepam) were consistent with the observed values reported by Adachi et al. within 2.1-fold difference. Thus, intestinal mdr1a function can be reconstructed by our pharmacoproteomic modeling approach. Furthermore, we evaluated regional differences in protein expression levels of mouse intestinal transporters. Sixteen (mdr1a, mrp4, bcrp, abcg5, abcg8, glut1, 4f2hc, sglt1, lat2, pept1, mct1, slc22a18, ostβ, villin1, Na(+)/K(+)-ATPase, γ-gtp) out of 46 target molecules were detected by employing our established quantitative targeted absolute proteomics technique. The protein expression amounts of mdr1a and bcrp increased progressively from duodenum to ileum. Sglt1, lat2, and 4f2hc were highly expressed in jejunum and ileum. Mct1 and ostβ were highly expressed in ileum. The quantitative expression profiles established here should be helpful to understand and predict intestinal transporter functions.

Drug-drug interactions (DDIs) and associated toxicity from cardiovascular drugs represents a major problem for effective co-administration of cardiovascular therapeutics. A significant amount of drug toxicity from DDIs occurs because of drug interactions and multiple cardiovascular drug binding to the efflux transporter P-glycoprotein (Pgp), which is particularly problematic for cardiovascular drugs because of their relatively low therapeutic indexes. The calcium channel antagonist, verapamil and the cardiac glycoside, digoxin, exhibit DDIs with Pgp through non-competitive inhibition of digoxin transport, which leads to elevated digoxin plasma concentrations and digoxin toxicity. In the present study, verapamil-induced ATPase activation kinetics were biphasic implying at least two verapamil-binding sites on Pgp, whereas monophasic digoxin activation of Pgp-coupled ATPase kinetics suggested a single digoxin-binding site. Using intrinsic protein fluorescence and the saturation transfer double difference (STDD) NMR techniques to probe drug-Pgp interactions, verapamil was found to have little effect on digoxin-Pgp interactions at low concentrations of verapamil, which is consistent with simultaneous binding of the drugs and non-competitive inhibition. Higher concentrations of verapamil caused significant disruption of digoxin-Pgp interactions that suggested overlapping and competing drug-binding sites. These interactions correlated to drug-induced conformational changes deduced from acrylamide quenching of Pgp tryptophan fluorescence. Also, Pgp-coupled ATPase activity kinetics measured with a range of verapamil and digoxin concentrations fit well to a DDI model encompassing non-competitive and competitive inhibition of digoxin by verapamil. The results and previous transport studies were combined into a comprehensive model of verapamil-digoxin DDIs encompassing drug binding, ATP hydrolysis, transport and conformational changes., (© 2016 Authors.)

Introduction: 2-Isopropyl-5-[methyl-(2-phenylethyl)amino]-2-phenylpentanenitrile (emopamil; EMP) is a calcium channel blocker of the phenylalkylamine class, with weak substrate properties for P-glycoprotein (P-gp). A weak substrate for P-gp would be suitable for measuring enhanced P-gp function. This study was performed to synthesise (R)- and (S)-[(11)C]EMP and characterise their properties as P-gp tracers., Methods: We synthesised (R)- and (S)-[(11)C]EMP and compared their biodistribution, peripheral metabolism, and effects of the P-gp inhibitor cyclosporine A (CsA, 50 mg/kg). We compared the brain pharmacokinetics of (R)-[(11)C]EMP and (R)-[(11)C]verapamil [(R)-[(11)C]VER] at baseline and CsA pretreatment with small animal positron emission tomography (PET)., Results: (R)- and (S)-[(11)C]EMP were synthesised from (R)- and (S)-noremopamil, respectively, by methylation with [(11)C]methyl triflate in the presence of NaOH at room temperature. (R)- and (S)-[(11)C]EMP yields were ~30%, with specific activity>74 GBq/μmol and radiochemical purity>99%. (R)-[(11)C]EMP showed significantly greater uptake in the mouse brain than (S)-[(11)C]EMP. Both showed homogeneous non-stereoselective regional brain distributions. (R)- and (S)-[(11)C]EMP were rapidly metabolised to hydrophilic metabolites. Unchanged plasma (S)-[(11)C]EMP level was significantly lower than that of (R)-[(11)C]EMP 15 minutes post-injection, whilst>88% of radioactivity in the brain was intact at 15 minutes post-injection and was non-stereoselective. CsA pretreatment increased brain activity ~3-fold in mice, but was non-stereoselective. The baseline area-under-the-curve (AUC) of brain radioactivity (0-60 minutes) of (R)-[(11)C]EMP was 2-fold higher than that of (R)-[(11)C]VER, but their AUCs after CsA pretreatment were comparable., Conclusions: (R)-[(11)C]EMP is a novel tracer for imaging P-gp function with higher baseline uptake than (R)-[(11)C]VER., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The aim of this study was to evaluate the change in the expression and the activity of intestinal P-glycoprotein (efflux transporter) with progression of diabetes in rats. Diabetes was induced in Wistar rats using a combination of low dose streptozotocin along with high fat diet. The expression of intestinal P-glycoprotein significantly increased (P≤0.05) with the progression of diabetes which was inferred from the mRNA analysis of mdr1a and mdr1b genes in the ileum segment of rat intestine. Furthermore, a significant increase (P≤0.05) in Na(+)-K(+) ATPase activity was observed in the ileum segment of rat intestine with the progression of diabetes. As a result of this, a significant decrease in the intestinal uptake and peroral bioavailability of the P-glycoprotein substrates (verapamil and atorvastatin) was observed along with the progression of diabetes as compared to normal animals. To address this problem of impaired drug uptake and bioavailability, a reported P-glycoprotein inhibitor, epigallocatechin-3-gallate, was experimentally evaluated. The treatment with epigallocatechin-3-gallate resulted in significant reduction in the expression and activity of P-glycoprotein and subsequent improvement in the intestinal uptake and peroral bioavailability of both verapamil and atorvastatin in normal as well as in diabetic animals. The findings of this study rationalised the use and established the mechanism of action of epigallocatechin-3-gallate to overcome P-glycoprotein mediated drug efflux and will also be helpful in therapeutic drug monitoring in diabetes., (Copyright © 2015 Elsevier B.V. All rights reserved.)