Pharmacokinetics of lopinavir/ritonavir oral solution to treat COVID-19 in mechanically ventilated ICU patients.

BACKGROUND: The combination lopinavir/ritonavir is recommended to treat HIV-infected patients at the dose regimen of 400/100 mg q12h, oral route. The usual lopinavir trough plasma concentrations are 3000-8000 ng/mL. A trend towards a 28 day mortality reduction was observed in COVID-19-infected patients treated with lopinavir/ritonavir. OBJECTIVES: To assess the plasma concentrations of lopinavir and ritonavir in patients with severe COVID-19 infection and receiving lopinavir/ritonavir. PATIENTS AND METHODS: Mechanically ventilated patients with COVID-19 infection included in the French COVID-19 cohort and treated with lopinavir/ritonavir were included. Lopinavir/ritonavir combination was administered using the usual adult HIV dose regimen (400/100 mg q12h, oral solution through a nasogastric tube). A half-dose reduction to 400/100 mg q24h was proposed if lopinavir Ctrough was >8000 ng/mL, the upper limit considered as toxic and reported in HIV-infected patients. Lopinavir and ritonavir pharmacokinetic parameters were determined after an intensive pharmacokinetic analysis. Biological markers of inflammation and liver/kidney function were monitored. RESULTS: Plasma concentrations of lopinavir and ritonavir were first assessed in eight patients treated with lopinavir/ritonavir. Median (IQR) lopinavir Ctrough reached 27 908 ng/mL (15 928-32 627). After the dose reduction to 400/100 mg q24h, lopinavir/ritonavir pharmacokinetic parameters were assessed in nine patients. Lopinavir Ctrough decreased to 22 974 ng/mL (21 394-32 735). CONCLUSIONS: In mechanically ventilated patients with severe COVID-19 infections, the oral administration of lopinavir/ritonavir elicited plasma exposure of lopinavir more than 6-fold the upper usual expected range. However, it remains difficult to safely recommend its dose reduction without compromising the benefit of the antiviral strategy, and careful pharmacokinetic and toxicity monitoring are needed.

Drug-drug interactions of newly approved small molecule inhibitors for acute myeloid leukemia.

Several small molecule inhibitors (SMIs) have been recently approved for AML patients. These targeted therapies could be more tolerable than classical antineoplastics, but potential drug-drug interactions (DDI) are relatively frequent. Underestimation or lack of appropriate awareness and management of DDIs with SMIs can jeopardize therapeutic success in AML patients, which often require multiple concomitant medications in the context of prior comorbidities or for the prevention and treatment of infectious and other complications. In this systematic review, we analyze DDIs of glasdegib, venetoclax, midostaurin, quizartinib, gilteritinib, enasidenib, and ivosidenib. CYP3A4 is the main enzyme responsible for SMIs metabolism, and strong CYP3A4 inhibitors, such azoles, could increase drug exposure and toxicity; therefore dose adjustments (venetoclax, quizartinib, and ivosidenib) or alternative therapies or close monitoring (glasdegib, midostaurin, and gilteritinib) are recommended. Besides, coadministration of strong CYP3A4 inducers with SMIs should be avoided due to potential decrease of efficacy. Regarding tolerability, QTc prolongation is frequently observed for most of approved SMIs, and drugs with a potential to prolong the QTc interval and CYP3A4 inhibitors should be avoided and replaced by alternative treatments. In this study, we critically assess the DDIs of SMIs, and we summarize best management options for these new drugs and concomitant medications.

Effect of isavuconazole on tacrolimus and sirolimus serum concentrations in allogeneic hematopoietic stem cell transplant patients: A drug-drug interaction study.

INTRODUCTION: Isavuconazole, a triazole antifungal, is an inhibitor of cytochrome P450 3A4, which also metabolizes tacrolimus and sirolimus. In previous studies, isavuconazole administration increased tacrolimus and sirolimus area under the curve values by 2.3-fold and 1.8-fold, respectively, in healthy adults and tacrolimus concentration/dose (C/D) ratio by 1.3-fold in solid organ transplant patients. We aimed to determine the magnitude of effect of isavuconazole administration on tacrolimus and sirolimus C/D ratios in allogeneic hematopoietic stem cell transplant (alloHSCT) patients. METHODS: A retrospective, single-center, single-arm study in adult alloHSCT patients who received at least 10 days of combination therapy with isavuconazole and tacrolimus and/or sirolimus as inpatients or outpatients was conducted. Tacrolimus and sirolimus trough serum concentrations were measured up to twice weekly for up to 4 weeks. RESULTS: Twenty-two patients receiving tacrolimus and twenty patients receiving sirolimus met the inclusion criteria. The mean C/D ratio increased from baseline by 1.42-fold for tacrolimus during week 1 (P = 0.002) and up to 1.56-fold for sirolimus during week 2 (P = 0.02). For the remaining timepoints, tacrolimus and sirolimus C/D ratios were not statistically significantly different from baseline. CONCLUSION: In alloHSCT patients, modest increases in tacrolimus and sirolimus C/D ratios from baseline were observed within the first 2 weeks after initiation of isavuconazole.

Application of a physiologically based pharmacokinetic model for the prediction of mirabegron plasma concentrations in a population with severe renal impairment.

We previously verified a physiologically based pharmacokinetic (PBPK) model for mirabegron in healthy subjects using the Simcyp Simulator by incorporating data on the inhibitory effect on cytochrome P450 (CYP) 2D6 and a multi-elimination pathway mediated by CYP3A4, uridine 5'-diphosphate-glucuronosyltransferase (UGT) 2B7 and butyrylcholinesterase (BChE). The aim of this study was to use this PBPK model to assess the magnitude of drug-drug interactions (DDIs) in an elderly population with severe renal impairment (sRI), which has not been evaluated in clinical trials. We first determined the system parameters, and meta-analyses of literature data suggested that the abundance of UGT2B7 and the BChE activity in an elderly population with sRI was almost equivalent to and 20% lower than that in healthy young subjects, respectively. Other parameters, such as the CYP3A4 abundance, for an sRI population were used according to those built into the Simcyp Simulator. Second, we confirmed that the PBPK model reproduced the plasma concentration-time profile for mirabegron in an sRI population (simulated area under the plasma concentration-time curve (AUC) was within 1.5-times that of the observed value). Finally, we applied the PBPK model to simulate DDIs in an sRI population. The PBPK model predicted that the AUC for mirabegron with itraconazole (a CYP3A4 inhibitor) was 4.12-times that in healthy elderly subjects administered mirabegron alone, and predicted that the proportional change in AUC for desipramine (a CYP2D6 substrate) with mirabegron was greater than that in healthy subjects. In conclusion, the PBPK model was verified for the purpose of DDI assessment in an elderly population with sRI.

Assessment of inter-racial variability in CYP3A4 activity and inducibility among healthy adult males of Caucasian and South Asian ancestries.

PURPOSE: Cytochrome P450 (CYP) 3A4 is responsible for the metabolism of more than 30% of clinically used drugs. Inherent between subject variability in clearance of CYP3A4 substrates is substantial; by way of example, midazolam clearance varies by > 10-fold between individuals before considering the impact of extrinsic factors. Relatively little is known about inter-racial variability in the activity of this enzyme. METHODS: This study assessed inter-racial variability in midazolam exposure in a cohort (n = 30) of CYP3A genotyped, age-matched healthy males of Caucasian and South Asian ancestries. Midazolam exposure was assessed at baseline, following 7 days of rifampicin and following 3 days of clarithromycin. RESULTS: The geometric mean baseline midazolam area under the plasma concentration curve (AUC0-6) in Caucasians (1057 µg/L/min) was 27% greater than South Asians (768 µg/L/min). Similarly, the post-induction midazolam AUC0-6 in Caucasians (308 µg/L/min) was 50% greater than South Asians (154 µg/L/min), while the post-inhibition midazolam AUC0-6 in Caucasians (1834 µg/L/min) was 41% greater than South Asians (1079 µg/L/min). The difference in baseline AUC0-6 between Caucasians and South Asians was statistically significant (p ≤ 0.05), and a trend toward significance (p = 0.067) was observed for the post-induction AUC0-6 ratio, in both unadjusted and genotype adjusted analyses. CONCLUSIONS: Significantly higher midazolam clearance was observed in healthy age-matched males of South Asian compared to Caucasian ancestry that was not explained by differences in the frequency of CYP3A genotypes.

Quercetin nanoparticles alter pharmacokinetics of bromocriptine, reflecting its enhanced inhibitory action on liver and intestinal CYP 3A enzymes in rats.

1. Quercetin is a dietary flavonoid has extremely low water solubility and found to possess CYP3A inhibitory activity. The purpose of the present study was to evaluate the effect of quercetin and quercetin nanoparticles (NQC) on the pharmacokinetics of bromocriptine (BRO) in rats. 2. NQC prepared by antisolvent precipitation method and characterized by SEM and dissolution test. The following methods were used in this study i.e. in vitro liver and intestinal CYP3A microsomal activity and in vitro non-everted sac method. To confirm these findings, an in vivo pharmacokinetic study was also performed. 3. The results indicate that quercetin significantly (p < 0.05) inhibited the CYP3A activity in liver and intestinal microsomes. In non-everted sac study, the intestinal transport and Papp of BRO were significantly increased in NQC and quercetin groups. Furthermore, in vivo study revealed that the increased levels of Cmax and AUC were comparatively high in NQC pretreated group than quercetin group. In addition, pretreatment with quercetin and NQC significantly (p < 0.05) decreased the mean CL/F and Vd/F of BRO. 4. NQC pretreatment might be result in higher plasma levels of quercetin that could inhibit the CYP3A enzyme and enhanced the bioavailability of BRO.

Assessment of potential interaction between simvastatin and clarithromycin in healthy adult male subjects.

Cardiac patients with weak immune system are susceptible to bacterial infections. Their prescriptions frequently contain simvastatin and clarithromycin together. The objective of present project was to assess the potential interaction between simvastatin and clarithromycin by evaluating the clarithromycin effects on the pharmacokinetics of simvastatin in healthy adult male subjects. The study design comprised of two phases, used at interval of one week. In first phase simvastatin 20 mg alone was administered to each volunteer. In second phase, co-administration of simvastatin 20 mg with clarithromycin 250 mg was made under similar specified conditions. Blood samples were collected at specified time intervals. Simvastatin plasma concentrations were analyzed through High Performance Liquid Chromatography with UV detector at 238 nm wavelength. Using one compartment open model, MW/PHARM version 3.02 software program was used by F. Rombut for pharmacokinetic parameters calculation. Clarithromycin co-treatment resulted in 2.3 fold increase in maximum plasma concentration Cmax (from 2.47±0.34 ng.mL-1 to 5.66±1.18 ng.mL-1; p<0.05) and 3.9 fold increase in area under time versus concentration curve from 0 to 10 hours AUC0-10 (from 15.10±3.73 ng.hr.mL-1 to 58.49±15.73 ng.hr.mL-1; p<0.05) of simvastatin. These results suggest that co-prescription of simvastatin and clarithromycin should be avoided to minimize the adverse events resulting from high simvastatin concentration, without sacrificing therapeutic worth of simvastatin.

Autoinhibitory properties of the parent but not of the N-oxide metabolite contribute to infusion rate-dependent voriconazole pharmacokinetics.

AIMS: The pharmacokinetics of voriconazole show a nonlinear dose-exposure relationship caused by inhibition of its own CYP3A-dependent metabolism. Because the magnitude of autoinhibition also depends on voriconazole concentrations, infusion rate might modulate voriconazole exposure. The impact of four different infusion rates on voriconazole pharmacokinetics was investigated. METHODS: Twelve healthy participants received 100 mg voriconazole intravenous over 4 h, 400 mg over 6 h, 4 h, and 2 h in a crossover design. Oral midazolam (3 µg) was given at the end of infusion. Blood and urine samples were collected up to 48 h. Voriconazole and its N-oxide metabolite were quantified using high-performance liquid chromatography coupled to tandem mass spectrometry. Midazolam estimated metabolic clearance (eCLmet) was calculated using a limited sampling strategy. Voriconazole-N-oxide inhibition of cytochrome P450 (CYP) isoforms 2C19 and 3A4 were assessed with the P450-Glo luminescence assay. RESULTS: Area under the concentration-time curve for 400 mg intravenous voriconazole was 16% (90% confidence interval: 12-20%) lower when administered over 6 h compared to 2 h infusion. Dose-corrected area under the concentration-time curve for 100 mg over 4 h was 34% lower compared to 400 mg over 4 h. Midazolam eCLmet was 516 ml min-1 (420-640) following 100 mg 4 h-1 voriconazole, 152 ml min-1 (139-166) for 400 mg 6 h-1 , 192 ml min-1 (167-220) for 400 mg 4 h-1 , and 202 ml min-1 (189-217) for 400 mg 2 h-1 . Concentration giving 50% CYP inhibition of voriconazole N-oxide was 146 ± 23 µmol l-1 for CYP3A4, and 40.2 ± 4.2 µmol l-1 for CYP2C19. CONCLUSIONS: Voriconazole pharmacokinetics is modulated by infusion rate, an autoinhibitory contribution voriconazole metabolism by CYP3A and 2C19 and to a lesser extent its main N-oxide metabolite for CYP2C19. To avoid reduced exposure, the infusion rate should be 2 h.

Managing Drug-Drug Interaction Between Ombitasvir, Paritaprevir/Ritonavir, Dasabuvir, and Mycophenolate Mofetil.

No drug-drug interaction study has been conducted to date for the combination of ombitasvir, paritaprevir/ritonavir, dasabuvir (3D), and mycophenolic acid (MPA). We here report the case of a hepatitis C virus-infected patient treated with 3D and MPA for vasculitis. In light of the threat of drug-drug interaction, the concentration of MPA was measured before, during, and 15 days after the end of the 3D treatment. Similar values were found at all 3 time points, thus indicating that there is probably no need to adapt MPA dosage to 3D.

Use of Human Plasma Samples to Identify Circulating Drug Metabolites that Inhibit Cytochrome P450 Enzymes.

Drug interactions elicited through inhibition of cytochrome P450 (P450) enzymes are important in pharmacotherapy. Recently, greater attention has been focused on not only parent drugs inhibiting P450 enzymes but also on possible inhibition of these enzymes by circulating metabolites. In this report, an ex vivo method whereby the potential for circulating metabolites to be inhibitors of P450 enzymes is described. To test this method, seven drugs and their known plasma metabolites were added to control human plasma at concentrations previously reported to occur in humans after administration of the parent drug. A volume of plasma for each drug based on the known inhibitory potency and time-averaged concentration of the parent drug was extracted and fractionated by high-pressure liquid chromatography-mass spectrometry, and the fractions were tested for inhibition of six human P450 enzyme activities (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4). Observation of inhibition in fractions that correspond to the retention times of metabolites indicates that the metabolite has the potential to contribute to P450 inhibition in vivo. Using this approach, norfluoxetine, hydroxyitraconazole, desmethyldiltiazem, desacetyldiltiazem, desethylamiodarone, hydroxybupropion, erythro-dihydrobupropion, and threo-dihydrobupropion were identified as circulating metabolites that inhibit P450 activities at a similar or greater extent as the parent drug. A decision tree is presented outlining how this method can be used to determine when a deeper investigation of the P450 inhibition properties of a drug metabolite is warranted.

Physiologically based pharmacokinetic modeling to predict drug-drug interactions involving inhibitory metabolite: a case study of amiodarone.

Evaluation of drug-drug interaction (DDI) involving circulating inhibitory metabolites of perpetrator drugs has recently drawn more attention from regulatory agencies and pharmaceutical companies. Here, using amiodarone (AMIO) as an example, we demonstrate the use of physiologically based pharmacokinetic (PBPK) modeling to assess how a potential inhibitory metabolite can contribute to clinically significant DDIs. Amiodarone was reported to increase the exposure of simvastatin, dextromethorphan, and warfarin by 1.2- to 2-fold, which was not expected based on its weak inhibition observed in vitro. The major circulating metabolite, mono-desethyl-amiodarone (MDEA), was later identified to have a more potent inhibitory effect. Using a combined "bottom-up" and "top-down" approach, a PBPK model was built to successfully simulate the pharmacokinetic profile of AMIO and MDEA, particularly their accumulation in plasma and liver after a long-term treatment. The clinical AMIO DDIs were predicted using the verified PBPK model with incorporation of cytochrome P450 inhibition from both AMIO and MDEA. The closest prediction was obtained for CYP3A (simvastatin) DDI when the competitive inhibition from both AMIO and MDEA was considered, for CYP2D6 (dextromethorphan) DDI when the competitive inhibition from AMIO and the competitive plus time-dependent inhibition from MDEA were incorporated, and for CYP2C9 (warfarin) DDI when the competitive plus time-dependent inhibition from AMIO and the competitive inhibition from MDEA were considered. The PBPK model with the ability to simulate DDI by considering dynamic change and accumulation of inhibitor (parent and metabolite) concentration in plasma and liver provides advantages in understanding the possible mechanism of clinical DDIs involving inhibitory metabolites.

Physiologically based pharmacokinetic modeling to predict complex drug-drug interactions: a case study of AZD2327 and its metabolite, competitive and time-dependent CYP3A inhibitors.

4-{(R)-(3-Aminophenyl)[4-(4-fluorobenzyl)-piperazin-1-yl]methyl}-N,N-diethylbenzamide (AZD2327) is a highly potent and selective agonist of the δ-opioid receptor. AZD2327 and N-deethylated AZD2327 (M1) are substrates of cytochrome P450 3A (CYP3A4) and comprise a complex multiple inhibitory system that causes competitive and time-dependent inhibition of CYP3A4. The aim of the current work was to develop a physiologically based pharmacokinetic (PBPK) model to predict quantitatively the magnitude of CYP3A4 mediated drug-drug interaction with midazolam as the substrate. Integrating in silico, in vitro and in vivo PK data, a PBPK model was successfully developed to simulate the clinical accumulation of AZD2327 and its primary metabolite. The inhibition of CYP3A4 by AZD2327, using midazolam as a probe drug, was reasonably predicted. The predicted maximum concentration (Cmax) and area under the concentration-time curve (AUC) for midazolam were increased by 1.75 and 2.45-fold, respectively, after multiple dosing of AZD2327, indicating no or low risk for clinically relevant drug-drug interactions (DDI). These results are in agreement with those obtained in a clinical trial with a 1.4 and 1.5-fold increase in Cmax and AUC of midazolam, respectively. In conclusion, this model simulated DDI with less than a two-fold error, indicating that complex clinical DDI associated with multiple mechanisms, pathways and inhibitors (parent and metabolite) can be predicted using a well-developed PBPK model.

Investigation of combined CYP3A4 inductive/inhibitory properties by studying statin interactions: a model study with the renin inhibitor ACT-178882.

PURPOSE: ACT-178882, a direct renin inhibitor, was used as a model compound in an elaborate drug-drug interaction study with atorvastatin and simvastatin to explore complex CYP3A4 inductive and inhibitory properties. METHODS: Thirty-two healthy male subjects received single doses of 20 mg atorvastatin and 20 mg simvastatin on days 1, 9, 31, and 41. On days 6 to 33, 500 mg ACT-178882 was administered once daily. Plasma concentrations of ACT-178882, simvastatin, and atorvastatin were measured by LC-MS/MS. Routine safety assessments were performed throughout the study. RESULTS: Exposure (as based on area under the curve) to simvastatin and 6ß-hydroxyacid simvastatin increased (90 % confidence interval) 4.63-fold (3.90, 5.50) and 3.71-fold (3.19, 4.32), respectively, when comparing day 9 and day 1. On day 9, exposure to atorvastatin was similar but Cmax decreased, while both variables decreased for ortho-hydroxy atorvastatin when compared to day 1. On day 31, after prolonged administration of ACT-178882, exposure to atorvastatin, ortho-hydroxy atorvastatin, simvastatin, and 6ß-hydroxyacid simvastatin decreased by 14, 19, 21, and 27 %, respectively, when compared to day 9. However, on this day, exposure to simvastatin and its metabolite was still markedly higher when compared to day 1. Effects of ACT-178882 had largely dissipated on day 41. CONCLUSIONS: This design enabled the study of complex time-dependent effects on CYP3A4 activity with clinically relevant substrates.

Effects of Cytochrome P450 3A4 Induction and Inhibition on the Pharmacokinetics of BI 425809, a Novel Glycine Transporter 1 Inhibitor.

BACKGROUND AND OBJECTIVE: Increased glycine availability at the synaptic cleft may enhance N-methyl-D-aspartate receptor signalling and provide a promising therapeutic strategy for cognitive impairment associated with schizophrenia. These studies aimed to assess the pharmacokinetics of BI 425809, a potent glycine-transporter-1 inhibitor, when co-administered with a strong cytochrome P450 3A4 (CYP3A4) inhibitor (itraconazole) and inducer (rifampicin). METHODS: In vitro studies using recombinant CYPs, human liver microsomes, and human hepatocytes were conducted to determine the CYP isoforms responsible for BI 425809 metabolism. In addition, two open-label, fixed-treatment period, phase I studies in healthy male volunteers are described. Period 1: participants received oral BI 425809 25 mg (single dose) on day 1; period 2: participants received multiple doses, across 10 days, of oral itraconazole or rifampicin combined with a single dose of oral BI 425809 25 mg on day 4/7 of the itraconazole/rifampicin treatment, respectively. Pharmacokinetic and safety endpoints were assessed in the absence/presence of itraconazole/rifampicin and included area under the concentration-time curve (AUC) over the time interval 0-167 h (AUC0‒167; itraconazole), 0-168 h (AUC0‒168; rifampicin), or 0-infinity (AUC0-∞; rifampicin and itraconazole), maximum measured concentration (Cmax) of BI 425809, and adverse events. RESULTS: In vitro results suggested that CYP3A4 accounted for ≥ 90% of the metabolism of BI 425809. BI 425809 exposure (adjusted geometric mean ratio [%]) was higher in the presence of itraconazole (AUC0‒167: 265.3; AUC0-∞: 597.0; Cmax: 116.1) and lower in the presence of rifampicin (AUC0‒168: 10.3; AUC0-∞: 9.8; Cmax: 37.4) compared with BI 425809 alone. Investigational treatments were well tolerated. CONCLUSIONS: Systemic exposure of BI 425809 was altered in the presence of strong CYP3A4 modulators, corroborating in vitro results that CYP3A4 mediates a major metabolic pathway for BI 425809. TRIAL REGISTRATION NUMBER: NCT02342717 (registered on 15 January 2015) and NCT03082183 (registered on 10 March 2017).

Impact of the Selective Orexin-1 Receptor Antagonist ACT-539313 on the Pharmacokinetics of the CYP3A Probe Drug Midazolam in Healthy Male Subjects.

ACT-539313 is a potent and selective orexin-1 receptor antagonist. CYP3A is the major cytochrome P450 (CYP) enzyme involved in the metabolism and clearance of ACT-539313 in man. The main objective of this study was to investigate the effect of ACT-539313 on the pharmacokinetics of orally administered midazolam. Thereby, this single-center, open-label, fixed-sequence study investigated the CYP3A interaction potential of ACT-539313 following single- (on day 2) and repeated-dose (on day 11) twice-daily administration of 200 mg ACT-539313. Exposure to midazolam was higher during concomitant administration of single as well as after repeated doses of ACT-539313 over 10 days compared to midazolam alone (day 1). In the presence of ACT-539313, the geometric mean ratio of the maximum plasma concentration and the area under the plasma concentration-time curve from time 0 to 24 hours increased by 1.18- and 1.79-fold on day 2, and by 2.13- and 4.54-fold on day 11, respectively. A similar outcome was also shown in the additionally evaluated urinary 6ß-hydroxycortisol/cortisol ratio (6ß-CR), as the geometric mean ratio of the 6ß-CR showed a decrease to 0.78 on day 2 and to 0.61 on day 11. The most commonly reported adverse events (AEs) included somnolence and headache. All AEs were transient and of mild intensity. No treatment-related effects on vital signs, clinical laboratory, and electrocardiogram were observed. In summary, the observed corresponding decrease of both the validated, exogenous (midazolam/1-hydroxymidazolam ratio) and a frequently used endogenous (6ß-CR) marker of CYP3A activity is indicative of CYP3A inhibition occurring after ACT-539313 treatment.

Clopidogrel Increases Dasabuvir Exposure With or Without Ritonavir, and Ritonavir Inhibits the Bioactivation of Clopidogrel.

Dasabuvir is mainly metabolized by cytochrome P450 (CYP) 2C8 and is predominantly used in a regimen containing ritonavir. Ritonavir and clopidogrel are inhibitors of CYP3A4 and CYP2C8, respectively. In a randomized, crossover study in 12 healthy subjects, we examined the impact of clinical doses of ritonavir (for 5 days), clopidogrel (for 3 days), and their combination on dasabuvir pharmacokinetics, and the effect of ritonavir on clopidogrel. Clopidogrel, but not ritonavir, increased the geometric mean AUC0-∞ of dasabuvir 4.7-fold; range 2.0-10.1-fold (P = 8·10-7 ), compared with placebo. Clopidogrel and ritonavir combination increased dasabuvir AUC0-∞ 3.9-fold; range 2.1-7.9-fold (P = 2·10-6 ), compared with ritonavir alone. Ritonavir decreased the AUC0-4h of clopidogrel active metabolite by 51% (P = 0.0001), and average platelet inhibition from 51% without ritonavir to 31% with ritonavir (P = 0.0007). In conclusion, clopidogrel markedly elevates dasabuvir concentrations, and patients receiving ritonavir are at risk for diminished clopidogrel response.

Assessment of preclinical drug interactions of bedaquiline by a highly sensitive LC-ESI-MS/MS based bioanalytical method.

A continuous effort has been given to find out a new drug that is effective against tuberculosis (TB) from both susceptible and resistant strains of Mycobacterium tuberculosis. Bedaquiline represents a recently approved anti-TB drug, which has a unique mechanism of action to fight against multi drug resistance (MDR). Some severe side effects and drug-drug interactions are associated with the treatment of bedaquiline. Moreover, World Health Organisation (WHO) has also been provided guidelines in the year of 2013 for the use of bedaquiline and encourages additional investigation into it. Hence, the pharmacokinetics of bedaquiline upon coadministration with the drug has to be explored in the preclinical model and for which a liquid chromatography tandem mass spectrometry (LC-MS/MS) based bioanalytical method for quantitation of bedaquiline will be useful. A simple, sensitive and rapid LC-MS/MS method was developed, validated and successfully applied to drug interactions of bedaquiline upon coadministration with cytochrome P450 3A4 (CYP3A4) inducers/inhibitors orally in Wistar rats. Results reveal that ciprofloxacin and fluconazole have marked effect to hinder the pharmacokinetics of bedaquiline but isoniazid, verapamil and carbamazepine have no significant effect on bedaquiline pharmacokinetics. Overall, this new bioanalytical method for estimation of bedaquiline in rat plasma was found to be helpful to assess the pharmacokinetics of bedaquiline and very much useful for evaluation of preclinical drug-drug interaction before considering costly and perilous clinical exploration.

Impaired Rivaroxaban Clearance in Mild Renal Insufficiency With Verapamil Coadministration: Potential Implications for Bleeding Risk and Dose Selection.

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.

Amenamevir: Studies of Potential CYP3A-Mediated Pharmacokinetic Interactions With Midazolam, Cyclosporine, and Ritonavir in Healthy Volunteers.

Amenamevir (formerly ASP2151) is a helicase-primase inhibitor being developed for the treatment of herpesvirus infection. Amenamevir is both a substrate and inducer of cytochrome P450 (CYP) 3A4. Three studies were done in healthy volunteers to investigate potential CYP3A pharmacokinetic interactions with the following drugs: (1) Midazolam (probe substrate for CYP3A): After 10 days' pretreatment with amenamevir 400 mg daily, geometric mean maximum concentration of drug in blood plasma (Cmax ) and area under the plasma drug concentration-time curve from time zero to infinity (AUC0-∞ ) of midazolam 7.5 mg were about 68% and 51%, respectively, of those after midazolam alone. (2) Cyclosporine (substrate and inhibitor of CYP3A): After 5 days' pretreatment with cyclosporine 100 mg twice daily, geometric mean Cmax of amenamevir after 400-mg and 1200-mg single doses was, respectively, about 66% and 69%, and AUC0-∞ about 82% and 79%, of those after amenamevir alone. (3) Ritonavir (inhibitor of CYP3A): When given with single doses of ritonavir 600 mg, geometric mean Cmax of amenamevir after 400-mg and 1200-mg single doses was, respectively, about 1.4 and 1.6 times higher, and geometric mean AUC0-∞ about 2.6 and 3.3 times higher, than after amenamevir alone. Amenamevir has the potential to be involved in CYP3A-mediated pharmacokinetic interactions in clinical practice.