S-warfarin limited sampling strategy with a population pharmacokinetic approach to estimate exposure and cytochrome P450 (CYP) 2C9 activity in healthy adults.

PURPOSE: S-warfarin is used to phenotype cytochrome P450 (CYP) 2C9 activity. This study evaluated S-warfarin limited sampling strategy with a population pharmacokinetic (PK) approach to estimate CYP2C9 activity in healthy adults. METHODS: In 6 previously published studies, a single oral dose of warfarin 10 mg was administered alone or with a CYP2C9 inducer to 100 healthy adults. S-warfarin concentrations were obtained from adults during conditions when subjects were not on any prescribed medications. A population PK model was developed using non-linear mixed effects modeling. Limited sampling models (LSMs) using single- or 2-timepoint concentrations were compared with full PK profiles from intense sampling using empiric Bayesian post hoc estimations of S-warfarin AUC derived from the population PK model. Preset criterion for LSM selection and validation were a correlation coefficient (R2) >0.9, relative percent mean prediction error (%MPE) >-5 to <5%, relative percent mean absolute error (%MAE) ≤ 10%, and relative percent root mean squared error (%RMSE) ≤ 15%. RESULTS: S-warfarin concentrations (n=2540) were well described with a two-compartment model. Mean apparent oral clearance was 0.56 L/hr and volume of distribution was 35.5 L. Clearance decreased 33% with the CYP2C9 *3 allele and increased 42% with lopinavir/ritonavir co-administration. During CYP2C9 constitutive conditions, LSMs at 48 hr and at 72 hr as well as 2-timepoint LSMs were within acceptable limits for R2, %MPE, %MAE, and %RMSE. During CYP2C9 induction, S-warfarin LSMs had unacceptable %MPE, %MAE, and %RMSE. CONCLUSIONS: Phenotyping studies with S-warfarin in healthy subjects can utilize a single- and/or a 2-timepoint LSM with a population PK approach to estimate constitutive CYP2C9 activity.

Carbon-13 synthesis and NMR spectroscopic geometric isomer evaluation to support the filing of teriflunomide.

The two isotopomers of teriflunomide were synthesized starting from isotopically stable-labeled stocks of [13 C]potassium cyanide and [1-13 C]ethyl bromoacetate. The two 13 C-labeled compounds 1a, b were applied in several NMR studies to study the E/Z ratio in different matrices. In a solution, such as dimethyl sulfoxide (DMSO), a dynamic equilibrium between E/Z-isomers (ratio of 8:92) was determined by initial 13 C-carbon NMR experiments. To get insights into the E/Z ratio of teriflunomide under in vivo conditions, advanced heteronuclear NMR (heteronuclear Overhauser effect spectroscopy [HOESY]) in D2 O and mixtures of D2 O/plasma were performed. Whereas NMR experiments in mixtures of water and plasma failed owing to extreme line broadening, NMR spectra in water at pH 7.4 showed only the Z-isomer.

Effect of eliglustat on the pharmacokinetics of digoxin, metoprolol, and oral contraceptives and absorption of eliglustat when coadministered with acid-reducing agents.

Eliglustat is an oral substrate reduction therapy indicated for patients with Gaucher disease type 1. Based on in vitro data, clinical trials were conducted to assess the potential for drug-drug interactions between eliglustat and digoxin (P-glycoprotein substrate), metoprolol (sensitive CYP2D6 substrate), a combined oral contraceptive (CYP3A substrate), and acid-reducing agents. Healthy subjects were enrolled in four Phase 1 clinical studies to evaluate the effect of eliglustat on the pharmacokinetics, safety, and tolerability of digoxin (N = 28), metoprolol (N = 14), and a combined oral contraceptive (N = 30) and the effect of acid-reducing agents on eliglustat pharmacokinetics, safety, and tolerability (N = 24). Coadministration resulted in increased exposure to digoxin (1.49-fold) and metoprolol (2-fold) with eliglustat, negligible effects on oral contraceptive pharmacokinetics with eliglustat, and a negligible effect of acid-reducing agents on eliglustat pharmacokinetics. Across all studies, eliglustat was well-tolerated. One serious adverse event (spontaneous abortion) and one discontinuation due to an adverse event (urinary tract infection) were reported, both during the acid-reducing agents study. When eliglustat is coadministered with medications that are P-glycoprotein or CYP2D6 substrates, lower doses of these concomitant medications may be required. Eliglustat may be coadministered with oral contraceptives and acid-reducing agents without dose modifications for either drug.

Effects of paroxetine, ketoconazole, and rifampin on the metabolism of eliglustat, an oral substrate reduction therapy for Gaucher disease type 1.

Eliglustat is an oral glucosylceramide synthase inhibitor indicated for the long-term treatment of adults with Gaucher disease type 1 and CYP2D6 extensive, intermediate, or poor metabolizer phenotypes. Eliglustat is metabolized primarily by CYP2D6 and to a lesser extent by CYP3A4 and is a substrate of P-glycoprotein (P-gp). Three studies evaluated the effects of paroxetine (strong CYP2D6 inhibitor), ketoconazole (strong CYP3A4 and P-gp inhibitor), and rifampin (strong CYP3A4/P-gp inducer; OATP inhibitor) on the pharmacokinetics of orally administered eliglustat in healthy adults. An 8.9-fold increase in eliglustat exposure following co-administration of multiple-dose eliglustat and paroxetine is attributed to inhibition of CYP2D6-mediated metabolism of eliglustat by paroxetine. A 4.3-fold increase in eliglustat exposure following co-administration of multiple-dose eliglustat and ketoconazole is attributed to inhibition of CYP3A4-mediated metabolism and/or P-gp-mediated transport of eliglustat by ketoconazole. Co-administration of eliglustat with oral doses of rifampin reduced eliglustat exposure by >85% due to induction of CYP3A4/P-gp by rifampin, while a single intravenous dose of rifampin had no effect on eliglustat, confirming that eliglustat is not an OATP substrate. Depending on CYP2D6 metabolizer phenotype, co-administration of eliglustat with CYP2D6 and/or CYP3A inhibitors or CYP3A inducers may alter eliglustat exposure, warrant dosage adjustment or use with caution, or be contraindicated.

Impact of hepatic and renal impairment on the pharmacokinetics and tolerability of eliglustat therapy for Gaucher disease type 1.

Eliglustat is a first-line oral therapy for adults with Gaucher disease type 1 (GD1) who have extensive (EM), intermediate (IM), or poor (PM) CYP2D6 metabolizer phenotypes. It was initially not recommended in GD1 patients with hepatic or renal impairment due to insufficient data. Two Phase 1 studies (NCT02536937/NCT02536911) evaluated the effects of hepatic and renal impairment on pharmacokinetics and tolerability following a single 84-mg dose of eliglustat. Compared to matched healthy EM subjects (n = 7 for both studies), geometric means for eliglustat maximum concentration (Cmax) and area under the plasma concentration versus time curve extrapolated to infinity (AUC) were not substantially different in EMs with mild hepatic impairment (n = 6), higher in EMs with moderate hepatic impairment (n = 7), and similar in EMs with severe renal impairment (n = 7). Higher exposures of eliglustat at steady-state were predicted using a physiologically-based pharmacokinetic (PBPK) model in EMs with mild or moderate hepatic impairment compared with normal hepatic function after repeated 84-mg eliglustat doses. Higher exposures of eliglustat were also predicted in EMs with mild hepatic impairment after coadministration with a CYP2D6 or CYP3A inhibitor with repeated doses. Based on these results, the eliglustat drug label was revised for patients with hepatic or renal impairment.

Dried Blood Spot Methodology in Combination With Liquid Chromatography/Tandem Mass Spectrometry Facilitates the Monitoring of Teriflunomide.

BACKGROUND: Teriflunomide, a once-daily oral immunomodulator approved for treatment of relapsing-remitting multiple sclerosis, is eliminated slowly from plasma. If necessary to rapidly lower plasma concentrations of teriflunomide, an accelerated elimination procedure using cholestyramine or activated charcoal may be used. The current bioanalytical assay for determination of plasma teriflunomide concentration requires laboratory facilities for blood centrifugation and plasma storage. An alternative method, with potential for greater convenience, is dried blood spot (DBS) methodology. Analytical and clinical validations are required to switch from plasma to DBS (finger-prick sampling) methodology. METHODS: Using blood samples from healthy subjects, an LC-MS/MS assay method for quantification of teriflunomide in DBS over a range of 0.01-10 mcg/mL was developed and validated for specificity, selectivity, accuracy, precision, reproducibility, and stability. Results were compared with those from the current plasma assay for determination of plasma teriflunomide concentration. RESULTS: Method was specific and selective relative to endogenous compounds, with process efficiency ∼88%, and no matrix effect. Inaccuracy and imprecision for intraday and interday analyses were <15% at all concentrations tested. Quantification of teriflunomide in DBS assay was not affected by blood deposit volume and punch position within spot, and hematocrit level had a limited but acceptable effect on measurement accuracy. Teriflunomide was stable for at least 4 months at room temperature, and for at least 24 hours at 37°C with and without 95% relative humidity, to cover sampling, drying, and shipment conditions in the field. The correlation between DBS and plasma concentrations (R = 0.97), with an average blood to plasma ratio of 0.59, was concentration independent and constant over time. CONCLUSIONS: DBS sampling is a simple and practical method for monitoring teriflunomide concentrations.

S-Warfarin Limited Sampling Models to Estimate Area Under the Concentration Versus Time Curve for Cytochrome P450 2C9 Baseline Activity and After Induction.

BACKGROUND: Phenotyping cytochrome P450 (CYP) 2C9 activity using S-warfarin has routinely required extensive blood sampling over at least 96 hours after dose to estimate the area under the concentration time curve from zero to infinity (AUC). Alternatively, S-warfarin limited sampling models (LSMs) using one or 2 concentration timepoints have been proposed to estimate AUC. This study evaluated whether S-warfarin LSMs accurately estimate CYP2C9 baseline and induction conditions in healthy adults and in advanced-stage cancer patients. METHODS: Plasma S-warfarin concentrations from healthy adults (n = 92) and in advanced-stage cancer patients (n = 22) were obtained from 6 published studies where a single 10 mg dose of oral warfarin was administered at CYP2C9 baseline and induction conditions. S-warfarin observed AUC was determined by noncompartmental analysis, whereas estimated AUC was calculated from the LSMs. Bias and precision were assessed by percent mean prediction error, percent mean absolute error, and percent root mean square error. RESULTS: Different results were observed for S-warfarin LSMs in estimating CYP2C9 baseline activity, with most studies resulting in unacceptable bias and precision. The percent mean prediction error, percent mean absolute error, and/or percent root mean square error exceeded acceptable limits for LSMs in patients with advanced-stage cancer and during CYP2C9 induction with lopinavir/ritonavir. CONCLUSIONS: The differing results during CYP2C9 baseline conditions, as well as unacceptable bias and precision in patients with advanced cancer and during CYP2C9 induction, considerably limit the widespread use of previously published S-warfarin LSMs.

Surinabant, a selective cannabinoid receptor type 1 antagonist, inhibits Δ9-tetrahydrocannabinol-induced central nervous system and heart rate effects in humans.

AIM: Cannabinoid receptor type 1 (CB1 ) antagonists have been developed for the treatment of obesity and associated risk factors. Surinabant is a high affinity CB1 antagonist in vitro. The aim of this study was to assess the magnitude of inhibition by surinabant of CNS effects and heart rate induced by Δ(9) -tetrahydrocannabinol (THC) in humans. METHODS: This was a double-blind, placebo-controlled, randomized, four period six sequence crossover study. Thirty healthy young male occasional cannabis users (<1 per week) were included. A single oral dose of surinabant (5, 20 or 60 mg) or placebo was administered followed 1.5 h later by four intrapulmonary THC doses (2, 4, 6 and 6 mg) or vehicle, administered at 1 h intervals. The wash-out period was 14-21 days. Subjective and objective pharmacodynamic (PD) measurements were performed. A population PK-PD model for THC and surinabant quantified PK and PD effects. RESULTS: Surinabant 20 and 60 mg inhibited all THC-induced PD effects in a similar range for both doses with inhibition ratios ranging from 68.3% (95% CI = 32.5, 104.2; heart rate) to 91.1% (95% CI = 30.3, 151.8; body sway). IC50 ranged from 22.0 ng ml(-1) [relative standard error (RSE) = 45.2%; body sway] to 58.8 ng ml(-1) (RSE = 44.2%; internal perception). Surinabant 5 mg demonstrated no significant effects. CONCLUSIONS: The dose-related inhibition by surinabant, without any effect of its own, suggests that this compound behaves as a CB1 receptor antagonist in humans at these concentrations. A single surinabant dose between 5 to 20 mg and above was able to antagonize THC-induced effects in humans.

Pharmacokinetic assessment of a five-probe cocktail for CYPs 1A2, 2C9, 2C19, 2D6 and 3A.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: * Numerous cocktails using concurrent administration of several cytochrome P450 (CYP) isoform-selective probe drugs have been reported to investigate drug-drug interactions in vivo. * This approach has several advantages: characterize the inhibitory or induction potential of compounds in development toward the CYP enzymes identified in vitro in an in vivo situation, assess several enzymes in the same trial, and have complete in vivo information about potential CYP-based drug interactions. WHAT THIS STUDY ADDS: * This study describes a new cocktail containing five probe drugs that has never been published. * This cocktail can be used to test the effects of a new chemical entity on multiple CYP isoforms in a single clinical study: CYP1A2 (caffeine), CYP2C9 (warfarin), CYP2C19 (omeprazole), CYP2D6 (metoprolol), and CYP3A (midazolam) and was designed to overcome potential liabilities of other reported cocktails. AIMS: To assess the pharmacokinetics (PK) of selective substrates of CYP1A2 (caffeine), CYP2C9 (S-warfarin), CYP2C19 (omeprazole), CYP2D6 (metoprolol) and CYP3A (midazolam) when administered orally and concurrently as a cocktail relative to the drugs administered alone. METHODS: This was an open-label, single-dose, randomized, six-treatment six-period six-sequence William's design study with a wash-out of 7 or 14 days. Thirty healthy male subjects received 100 mg caffeine, 100 mg metoprolol, 0.03 mg kg(-1) midazolam, 20 mg omeprazole and 10 mg warfarin individually and in combination (cocktail). Poor metabolizers of CYP2C9, 2C19 and 2D6 were excluded. Plasma samples were obtained up to 48 h for caffeine, metoprolol and omeprazole, 12 h for midazolam, 312 h for warfarin and the cocktail. Three different validated liquid chromatography tandem mass spectrometry methods were used. Noncompartmental PK parameters were calculated. Log-transformed C(max), AUC(last) and AUC for each analyte were analysed with a linear mixed effects model with fixed term for treatment, sequence and period, and random term for subject within sequence. Point estimates (90% CI) for treatment ratios (individual/cocktail) were computed for each analyte C(max), AUC(last) and AUC. RESULTS: There was no PK interaction between the probe drugs when administered in combination as a cocktail, relative to the probes administered alone, as the 90% CI of the PK parameters was within the prespecified bioequivalence limits of 0.80, 1.25. CONCLUSION: The lack of interaction between probes indicates that this cocktail could be used to evaluate the potential for multiple drug-drug interactions in vivo.