Human Pharmacokinetic and CYP3A Drug-Drug Interaction Prediction of GDC-2394 Using Physiologically Based Pharmacokinetic Modeling and Biomarker Assessment.

Physiologically based pharmacokinetic (PBPK) modeling was used to predict the human pharmacokinetics and drug-drug interaction (DDI) of GDC-2394. PBPK models were developed using in vitro and in vivo data to reflect the oral and intravenous PK profiles of mouse, rat, dog, and monkey. The learnings from preclinical PBPK models were applied to a human PBPK model for prospective human PK predictions. The prospective human PK predictions were within 3-fold of the clinical data from the first-in-human study, which was used to optimize and validate the PBPK model and subsequently used for DDI prediction. Based on the majority of PBPK modeling scenarios using the in vitro CYP3A induction data (mRNA and activity), GDC-2394 was predicted to have no-to-weak induction potential at 900 mg twice daily (BID). Calibration of the induction mRNA and activity data allowed for the convergence of DDI predictions to a narrower range. The plasma concentrations of the 4ß-hydroxycholesterol (4ß-HC) were measured in the multiple ascending dose study to assess the hepatic CYP3A induction risk. There was no change in plasma 4ß-HC concentrations after 7 days of GDC-2394 at 900 mg BID. A dedicated DDI study found that GDC-2394 has no induction effect on midazolam in humans, which was reflected by the totality of predicted DDI scenarios. This work demonstrates the prospective utilization of PBPK for human PK and DDI prediction in early drug development of GDC-2394. PBPK modeling accompanied with CYP3A biomarkers can serve as a strategy to support clinical pharmacology development plans. SIGNIFICANCE STATEMENT: This work presents the application of physiologically based pharmacokinetic modeling for prospective human pharmacokinetic (PK) and drug-drug interaction (DDI) prediction in early drug development. The strategy taken in this report represents a framework to incorporate various approaches including calibration of in vitro induction data and consideration of CYP3A biomarkers to inform on the overall CYP3A-related DDI risk of GDC-2394.

Assessment of CYP-Mediated Drug Interactions for Enasidenib Based on a Cocktail Study in Patients with Relapse or Refractory Acute Myeloid Leukemia or Myelodysplastic Syndrome.

As a selective and potent inhibitor targeting the isocitrate dehydrogenase-2 (IDH2) mutant protein, enasidenib obtained approval from the US Food and Drug Administration (FDA) in 2017 for adult patients with acute myeloid leukemia (AML) with an IDH2 mutation. In vitro investigations demonstrated that enasidenib affects various drug metabolic enzymes and transporters. This current investigation aimed to assess enasidenib on the pharmacokinetics (PKs) of CYP substrates, including dextromethorphan (CYP2D6 probe drug), flurbiprofen (CYP2C9 probe drug), midazolam (CYP3A4 probe drug), omeprazole (CYP2C19 probe drug), and pioglitazone (CYP2C8 probe drug), in patients with AML or myelodysplastic syndrome. Results showed that following the co-administration of enasidenib (100 mg, once daily) for 28 days, the PK parameters AUC(0-∞) and Cmax of dextromethorphan increased by 1.37 (90% confidence interval (CI): 0.96, 1.96) and 1.24 (90% CI: 0.94, 1.65)-fold, respectively, compared to dextromethorphan alone. For flurbiprofen, these parameters increased by 1.14 (90%CI: 1.01, 1.29) and 0.97 (90% CI 0.86, 1.08)-fold, respectively, when compared to flurbiprofen alone. Conversely, midazolam exhibited decreases to 0.57 (90% CI 0.34, 0.97) and 0.77 (90% CI 0.39, 1.53)-fold, respectively, in comparison to midazolam alone. The parameters for omeprazole increased by 1.86 (90% CI: 1.33, 2.60) and 1.47 (0.93, 2.31)-fold, respectively, compared to omeprazole alone, while those for pioglitazone decreased to 0.80 (90% CI: 0.62, 1.03) and 0.87 (90% CI: 0.65, 1.16)-fold, respectively, in comparison to pioglitazone alone. These findings provide valuable insights into dose recommendations concerning drugs acting as substrates of CYP2D6, CYP2C9, CYP3A4, CYP2C19, and CYP2C8 when administered concurrently with enasidenib.

Clinical assessment of momelotinib drug-drug interactions via CYP3A metabolism and transporters.

Momelotinib-approved for treatment of myelofibrosis in adults with anemia-and its major active metabolite, M21, were assessed as drug-drug interaction (DDI) victims with a strong cytochrome P450 (CYP) 3A4 inhibitor (multiple-dose ritonavir), an organic anion transporting polypeptide (OATP) 1B1/1B3 inhibitor (single-dose rifampin), and a strong CYP3A4 inducer (multiple-dose rifampin). Momelotinib DDI perpetrator potential (multiple-dose) was evaluated with CYP3A4 and breast cancer resistance protein (BCRP) substrates (midazolam and rosuvastatin, respectively). DDI was assessed from changes in maximum plasma concentration (Cmax), area under the concentration-time curve (AUC), time to reach Cmax, and half-life. The increase in momelotinib (23% Cmax, 14% AUC) or M21 (30% Cmax, 24% AUC) exposure with ritonavir coadministration was not clinically relevant. A moderate increase in momelotinib (40% Cmax, 57% AUC) and minimal change in M21 was observed with single-dose rifampin. A moderate decrease in momelotinib (29% Cmax, 46% AUC) and increase in M21 (31% Cmax, 15% AUC) were observed with multiple-dose rifampin compared with single-dose rifampin. Due to potentially counteracting effects of OATP1B1/1B3 inhibition and CYP3A4 induction, multiple-dose rifampin did not significantly change momelotinib pharmacokinetics compared with momelotinib alone (Cmax no change, 15% AUC decrease). Momelotinib did not alter the pharmacokinetics of midazolam (8% Cmax, 16% AUC decreases) or 1'-hydroxymidazolam (14% Cmax, 16% AUC decreases) but increased rosuvastatin Cmax by 220% and AUC by 170%. Safety findings were mild in this short-term study in healthy volunteers. This analysis suggests that momelotinib interactions with OATP1B1/1B3 inhibitors and BCRP substrates may warrant monitoring for adverse reactions or dose adjustments.

Midostaurin drug interaction profile: a comprehensive assessment of CYP3A, CYP2B6, and CYP2C8 drug substrates, and oral contraceptives in healthy participants.

PURPOSE: Midostaurin, approved for treating FLT-3-mutated acute myeloid leukemia and advanced systemic mastocytosis, is metabolized by cytochrome P450 (CYP) 3A4 to two major metabolites, and may inhibit and/or induce CYP3A, CYP2B6, and CYP2C8. Two studies investigated the impact of midostaurin on CYP substrate drugs and oral contraceptives in healthy participants. METHODS: Using sentinel dosing for participants' safety, the effects of midostaurin at steady state following 25-day (Study 1) or 24-day (Study 2) dosing with 50 mg twice daily were evaluated on CYP substrates, midazolam (CYP3A4), bupropion (CYP2B6), and pioglitazone (CYP2C8) in Study 1; and monophasic oral contraceptives (containing ethinylestradiol [EES] and levonorgestrel [LVG]) in Study 2. RESULTS: In Study 1, midostaurin resulted in a 10% increase in midazolam peak plasma concentrations (Cmax), and 3-4% decrease in total exposures (AUC). Bupropion showed a 55% decrease in Cmax and 48-49% decrease in AUCs. Pioglitazone showed a 10% decrease in Cmax and 6% decrease in AUC. In Study 2, midostaurin resulted in a 26% increase in Cmax and 7-10% increase in AUC of EES; and a 19% increase in Cmax and 29-42% increase in AUC of LVG. Midostaurin 50 mg twice daily for 28 days ensured that steady-state concentrations of midostaurin and the active metabolites were achieved by the time of CYP substrate drugs or oral contraceptive dosing. No safety concerns were reported. CONCLUSION: Midostaurin neither inhibits nor induces CYP3A4 and CYP2C8, and weakly induces CYP2B6. Midostaurin at steady state has no clinically relevant PK interaction on hormonal contraceptives. All treatments were well tolerated.

Assessment of the CYP3A4 Induction Potential by Carbamazepine: Insights from Two Clinical DDI Studies and PBPK Modeling.

In the past, rifampicin was well-established as strong index CYP3A inducer in clinical drug-drug interaction (DDI) studies. However, due to identified potentially genotoxic nitrosamine impurities, it should not any longer be used in healthy volunteer studies. Available clinical data suggest carbamazepine as an alternative to rifampicin as strong index CYP3A4 inducer in clinical DDI studies. Further, physiologically-based pharmacokinetic (PBPK) modeling is a tool with increasing importance to support the DDI risk assessment of drugs during drug development. CYP3A4 induction properties and the safety profile of carbamazepine were investigated in two open-label, fixed sequence, crossover clinical pharmacology studies in healthy volunteers using midazolam as a sensitive index CYP3A4 substrate. Carbamazepine was up-titrated from 100 mg twice daily (b.i.d.) to 200 mg b.i.d., and to a final dose of 300 mg b.i.d. for 10 consecutive days. Mean area under plasma concentration-time curve from zero to infinity (AUC(0-∞)) of midazolam consistently decreased by 71.8% (ratio: 0.282, 90% confidence interval (CI): 0.235-0.340) and 67.7% (ratio: 0.323, 90% CI: 0.256-0.407) in study 1 and study 2, respectively. The effect was adequately described by an internally developed PBPK model for carbamazepine which has been made freely available to the scientific community. Further, carbamazepine was safe and well-tolerated in the investigated dosing regimen in healthy participants. The results demonstrated that the presented design is appropriate for the use of carbamazepine as alternative inducer to rifampicin in DDI studies acknowledging its CYP3A4 inductive potency and safety profile.

Assessment of the potential of the MET inhibitor tepotinib to affect the pharmacokinetics of CYP3A4 and P-gp substrates.

Tepotinib is a highly selective, potent, mesenchymal-epithelial transition factor (MET) inhibitor, approved for the treatment of non-small cell lung cancer harboring MET exon 14 skipping alterations. The aims of this work were to investigate the potential for drug-drug interactions via cytochrome P450 (CYP) 3A4/5 or P-glycoprotein (P-gp) inhibition. In vitro studies were conducted in human liver microsomes, human hepatocyte cultures and Caco-2 cell monolayers to investigate whether tepotinib or its major metabolite (MSC2571109A) inhibited or induced CYP3A4/5 or inhibited P-gp. Two clinical studies were conducted to investigate the effect of multiple dose tepotinib (500 mg once daily orally) on the single dose pharmacokinetics of a sensitive CYP3A4 substrate (midazolam 7.5 mg orally) and a P-gp substrate (dabigatran etexilate 75 mg orally) in healthy participants. Tepotinib and MSC2571109A showed little evidence of direct or time-dependent CYP3A4/5 inhibition (IC50 > 15 µM) in vitro, although MSC2571109A did show mechanism-based CYP3A4/5 inhibition. Tepotinib did not induce CYP3A4/5 activity in vitro, although both tepotinib and MSC2571109A increased CYP3A4 mRNA. In clinical studies, tepotinib had no effect on the pharmacokinetics of midazolam or its metabolite 1'-hydroxymidazolam. Tepotinib increased dabigatran maximum concentration and area under the curve extrapolated to infinity by 38% and 51%, respectively. These changes were not considered to be clinically relevant. Tepotinib was considered safe and well tolerated in both studies. The potential of tepotinib to cause clinically relevant DDI with CYP3A4- or P-gp-dependent drugs at the clinical dose is considered low. Study 1 (midazolam): NCT03628339 (registered 14 August 2018). Study 2 (dabigatran): NCT03492437 (registered 10 April 2018).

Therapeutic Protein Drug Interaction Potential in Subjects With Psoriasis: An Assessment Based on Population Pharmacokinetic Analyses of Sensitive Cytochrome P450 Probe Substrates.

Elevated cytokine levels in inflammatory diseases are associated with downregulation of certain cytochrome P450 (CYP) enzymes. Upon treatment with some cytokine-targeting therapeutic proteins, the CYP enzymes levels may be restored resulting in therapeutic protein-mediated drug interactions (TP-DI). These analyses characterized the worst-case scenario for CYP1A2, 2C9, and 3A-based TP-DI potential in patients with psoriasis by comparing the pharmacokinetics of probe substrates between healthy volunteers and subjects with moderate to severe psoriasis. Data for the CYP probe substrates midazolam (CYP3A), caffeine (CYP1A2), and S-warfarin (CYP2C9) from 7 drug interaction studies (1 in patients with psoriasis and 6 in healthy subjects) were pooled to develop a population pharmacokinetics model for each substrate. A 2-compartment model with absorption lag time for midazolam, a 1-compartment model with 5 transit absorption compartments for caffeine, and a 3-compartment model with absorption lag time for S-warfarin best described the observed data. Apparent oral clearance and relative bioavailability for caffeine and S-warfarin were not significantly different between the subject populations. Psoriasis patients were estimated to have 17% lower midazolam oral bioavailability than healthy volunteers. Compounded with other covariate effects, the ratio of median post hoc area under the plasma concentration-time estimates in subjects with psoriasis relative to healthy subjects was 0.96, 1.13, and 0.65 for midazolam, caffeine, and S-warfarin, respectively. Therefore, inflammation in psoriasis had no relevant effect on reducing CYP1A2, 2C9, and 3A activities in vivo and no significant TP-DIs mediated through these enzymes are expected in patients with psoriasis. This approach can potentially be used in lieu of dedicated TP-DI studies to identify TP-DI risks within a disease area.

Drug-Drug Interaction Risk Assessment of Esaxerenone as a Perpetrator by In Vitro Studies and Static and Physiologically Based Pharmacokinetic Models.

Esaxerenone (CS-3150) is a novel, oral, nonsteroidal, selective mineralocorticoid receptor blocker approved for the treatment of hypertension in Japan. Here, the drug-drug interaction (DDI) potential of esaxerenone was evaluated in vitro, and its impact in clinical practice was estimated. Esaxerenone exhibited time-dependent inhibition and induction of CYP3A. When the clinical impacts of esaxerenone on the inhibition and induction of CYP3A were estimated separately by using a mechanistic static model, the predicted area under the curve ratios (AUCRs) of midazolam, a typical CYP3A substrate, were 1.80 and 0.31, respectively, suggesting that the DDI potential of esaxerenone cannot be neglected. Because it was suggested that DDIs mainly occur in the intestine, predictions using concentration-time profiles in each segment of the gastrointestinal tract were performed with GastroPlus, a physiologically based pharmacokinetic (PBPK) modeling software. The predicted AUCR of midazolam was approximately 1.2, which is close to that in a clinical study, despite the difficulty of predicting DDIs for compounds with both inhibition and induction effects. When only inhibition or induction was incorporated into a model, the AUCR of midazolam changed depending on the dosing period and dose level of esaxerenone and the timing of midazolam administration. However, the AUCR calculated by incorporating both effects remained almost constant. This study shows the ability of PBPK models to simulate weak DDIs via intestinal CYP3A and that esaxerenone has low DDI potential as a perpetrator because of the offset of inhibition and induction. SIGNIFICANCE STATEMENT: Weak CYP3A inhibition and/or induction sometimes cause DDIs in the intestine but not the liver. Because strong inhibitors maximally inhibit intestinal CYP3A, the predictability of weak DDIs in the intestine should be evaluated further. Here, we simulate the DDIs of esaxerenone as a perpetrator by using physiologically based pharmacokinetic modeling focusing on the intestine and offset of inhibition and induction.

A Novel Study Design Using Continuous Intravenous and Intraduodenal Infusions of Midazolam and Voriconazole for Mechanistic Quantitative Assessment of Hepatic and Intestinal CYP3A Inhibition.

The extent of a drug-drug interaction (DDI) mediated by cytochrome P450 (CYP) 3A inhibitors is highly variable during a dosing interval, as it depends on the temporal course of victim and perpetrator drug concentrations at intestinal and hepatic CYP3A expression sites. Capturing the time course of inhibition is therefore difficult using standard DDI studies assessing changes in area under the curve; thus, a novel design was developed. In a 4-period changeover pilot study, 6 healthy men received intraduodenal or intravenous infusions of the CYP3A substrate midazolam (MDZ) at a rate of 0.26 mg/h for 24 hours. This was combined with intraduodenal or intravenous infusion of the CYP3A inhibitor voriconazole (VRZ), administered at rates of 7.5 mg/h from 8 to 16 hours and of 15 mg/h from 16 to 24 hours, after starting midazolam administration. Plasma and urine concentrations of VRZ, MDZ, and its major metabolites were quantified by liquid chromatography-tandem mass spectrometry and analyzed by semiphysiological population pharmacokinetic nonlinear mixed-effects modeling. A model including mechanism-based inactivation of the metabolizing enzymes (maximum inactivation rate constant kinact , 2.83 h-1 ; dissociation rate constant KI , 9.33 µM) described the pharmacokinetics of VRZ well. By introducing competitive inhibition by VRZ on primary and secondary MDZ metabolism, concentration-time profiles, MDZ and its metabolites were captured appropriately. The model provides estimates of local concentrations of substrate and inhibitor at the major CYP3A expression sites and thus of the respective dynamic extent of inhibition. A combination of intravenous and intraduodenal infusions of inhibitors and substrates has the potential to provide a more accurate assessment of DDIs occurring in both gut wall and liver.

Critical Impact of Drug-Drug Interactions via Intestinal CYP3A in the Risk Assessment of Weak Perpetrators Using Physiologically Based Pharmacokinetic Models.

A great deal of effort has been being made to improve the accuracy of the prediction of drug-drug interactions (DDIs). In this study, we addressed CYP3A-mediated weak DDIs, in which a relatively high false prediction rate was pointed out. We selected 17 orally administered drugs that have been reported to alter area under the curve (AUC) of midazolam, a typical CYP3A substrate, 0.84-1.47 times. For weak CYP3A perpetrators, the predicted AUC ratio mainly depends on intestinal DDIs rather than hepatic DDIs because the drug concentration in the enterocytes is higher. Thus, DDI prediction using simulated concentration-time profiles in each segment of the digestive tract was made by physiologically based pharmacokinetic (PBPK) modeling software GastroPlus. Although mechanistic static models tend to overestimate the risk to ensure the safety of patients, some underestimation is reported about PBPK modeling. Our in vitro studies revealed that 16 out of 17 tested drugs exhibited time-dependent inhibition (TDI) of CYP3A, and the subsequent DDI simulation that ignored these TDIs provided false-negative results. This is considered to be the cause of past underestimation. Inclusion of the DDI parameters of all the known DDI mechanisms, reversible inhibition, TDI, and induction, which have opposite effects on midazolam AUC, to PBPK model was successful in improving predictability of the DDI without increasing false-negative prediction as trade-off. This comprehensive model-based analysis suggests the importance of the intestine in assessing weak DDIs via CYP3A and the usefulness of PBPK in predicting intestinal DDIs. SIGNIFICANCE STATEMENT: Although drug-drug interaction (DDI) prediction has been extensively performed previously, the accuracy of prediction for weak interactions via CYP3A has not been thoroughly investigated. In this study, we simulate DDIs considering drug concentration-time profile in the enterocytes and discuss the importance and the predictability of intestinal DDIs about weak CYP3A perpetrators.

A new similarity method for assessment of pharmacokinetic interaction between flucloxacillin and midazolam.

The purpose of this study was to develop a new similarity method to assess the drug-drug interaction between midazolam and flucloxacillin. Total quantum statistical moment (TQSM) of pharmacokinetic profiles were expressed by parameters AUCT, MRTT, VRTT et al. Statistical moment similarity (SMS) expressions were deduced to evaluate the similarity of the converted pharmacokinetic profiles. A trial of the pharmacokinetic interaction between midazolam and flucloxacillin by the SMS method was conducted. For midazolam, total quantum SMS (SMST) was 0.9582; total deviation was 0.0525; total variable probability was 4.18 %; total confidence of probability ß was 97.17 % under significance level 0.05; AUC0-∞ were 334.3±334.1 ng•h•mL-1 (after administration of midazolam alone) and 206.9±172.2 ng•h•mL-1 (after co-administration of midazolam and flucloxacillin), respectively. While, for 1'-hydroxy midazolam, SMST was 0.6920; total deviation was 0.3960; total variable probability was 30.80 %; total confidence of probability ß was 94.10 % under significance level 0.05; AUC0-∞ were 1364±810.7 ng•h•mL-1 (after administration of midazolam alone) and 1637±632.6 ng•h•mL-1 (after co-administration of midazolam and flucloxacillin), respectively. These results revealed that flucloxacillin might have weak pharmacokinetic interactions on midazolam metabolized into 1'-hydroxy midazolam, indicating that there was weak induction to CYP3A by flucloxacillin and that there was at least 30.80 % of metabolic behaviour in change with bioavailability decreased by 38.11 % that took effect to flucloxacillin metabolism for liver injury in CPY3A4 poor metabolic polymorphisms. SMS can be an optional method applied to characterize and analyze pharmacokinetic profiles.

Alteration of drug-metabolizing enzyme activity in palliative care patients: Microdosed assessment of cytochrome P450 3A.

BACKGROUND: Cytochrome P450 3A is the most relevant drug-metabolizing enzyme in humans as it is involved in the elimination of 50% of marketed drugs. Nothing is known about the activity of cytochrome P450 3A in palliative care patients who have complicated symptoms often associated with a terminal illness. AIM: In order to improve drug dosing in end-of-life care and to avoid drug interactions, cytochrome P450 3A activity was determined in patients of a palliative care unit under real-life clinical conditions. DESIGN: As midazolam is an established marker substance for cytochrome P450 3A activity, this single-arm prospective trial was designed to obtain a 4-h pharmacokinetic profile of midazolam after oral administration of a 10-µg dose from each enrolled patient. Plasma concentrations of midazolam and its primary metabolite 1'-hydroxy-midazolam were quantified by mass spectrometry techniques. Cytochrome P450 3A activity was calculated as partial metabolic clearance from a limited sampling area under the curve. All other drugs taken by the participating patients were considered, as well as recent blood test results and patients' diagnoses. The trial was registered at German Clinical Trials Register ( www.drks.de ): DRKS00011753. SETTING/PARTICIPANTS: The trial was carried out at a university palliative care unit under real-life clinical conditions. Every patient admitted to the ward was screened for possible participation, independent of the individual performance status. RESULTS: Partial metabolic clearance of midazolam in palliative care patients was 31.7 ± 32.1 L/h. This was a highly significant 40% reduction (p < 0.0001) in comparison with the cytochrome P450 3A activity of healthy subjects. CONCLUSION: Dosing of cytochrome P450 3A substrate drugs (e.g. macrolide antibiotics, benzodiazepines, calcium channel blockers) needs to be adjusted in palliative care patients; otherwise, escalation of debilitating symptoms due to drug interactions might occur.

A Comprehensive In Vivo and In Vitro Assessment of the Drug Interaction Potential of Red Ginseng.

Purpose: Red ginseng is one of the world's most popular herbal medicines; it exhibits a wide range of pharmacologic activities and is often co-ingested with other herbal and conventional medicines. This open-label, randomized, 3-period study investigated the in vivo herb-drug interaction potential for red ginseng extract with cytochrome P-450 (CYP) enzymes and organic anion-transporting polypeptide (OATP) 1B1. METHODS: Fifteen healthy male volunteers (22-28 years; 57.1-80.8 kg) were administered a single dose of cocktail probe substrates (caffeine 100 mg, losartan 50 mg, omeprazole 20 mg, dextromethorphan 30 mg, midazolam 2 mg, and pitavastatin 2 mg) and single or multiple doses of red ginseng extract for 15 days. FINDINGS: The pharmacokinetic profiles of the probe substrates and metabolites after single- or multiple-dose administration of red ginseng extracts were comparable to the corresponding profiles of the control group. The geometric mean ratio of AUC0-t and 90% CIs for the probe substrate drugs between the control and multiple doses of red ginseng for 15 days were within 0.8 to 1.25 (CYP2C9, CYP3A4, and OATP1B1 probe substrates) or slightly higher (CYP1A2, CYP2C19, and CYP2D6 probe substrates). Additional assessments of the in vitro drug interaction potential of red ginseng extracts and the ginsenoside Rb1 on drug-metabolizing enzymes and transporters using human liver microsomes, cryopreserved human hepatocytes, and transporter-overexpressed cells were negative. IMPLICATIONS: Red ginseng poses minimal risks for clinically relevant CYP- or OATP-mediated drug interactions and is well tolerated. Clinical Research Information Service registry no.

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.

Assessment of Pharmacokinetic Interactions Between Obeticholic Acid and Caffeine, Midazolam, Warfarin, Dextromethorphan, Omeprazole, Rosuvastatin, and Digoxin in Phase 1 Studies in Healthy Subjects.

INTRODUCTION: Obeticholic acid (OCA), a potent and selective farnesoid X receptor agonist, is indicated for the treatment of primary biliary cholangitis (PBC). We investigated the potential drug-drug interaction effect of OCA on metabolic CYP450 enzymes and drug transporters. METHODS: Five phase 1 single-center, open-label, fixed-sequence, inpatient studies were conducted in healthy adult subjects to evaluate the effect of oral daily doses of 10 or 25 mg OCA on single-dose plasma pharmacokinetics of specific probe substrates for enzymes CYP1A2 (caffeine, R-warfarin), CYP3A (midazolam, R-warfarin), CYP2C9 (S-warfarin), CYP2D6 (dextromethorphan), CYP2C19 (omeprazole), and drug transporters, BCRP/OATP1B1/OATP1B3 (rosuvastatin), and P-gp (digoxin). RESULTS: OCA showed no substantial suppression/inhibition of S-warfarin, digoxin, and dextromethorphan and weak interactions with caffeine, omeprazole, rosuvastatin, and midazolam. The maximal pharmacodynamic responses (E max) to warfarin-based INR, PT, and aPTT were reduced by 11%, 11%, and 1%, respectively, for the 10-mg dose group and by 7%, 7% and 0%, respectively, for the 25-mg dose group. Overall, drugs dosed in combination with OCA were well tolerated, and most adverse events were mild in severity. No clinically important trends were noted in laboratory evaluations, vital signs, or 12-lead ECGs. CONCLUSION: In these studies, OCA showed weak to no suppression/inhibition of metabolic enzymes and drug transporters at the highest recommended therapeutic dose in patients with PBC. On the basis on these analyses, monitoring and maintenance of target INR range are required during coadministration of OCA with drugs that are metabolized by CYP1A2 (R-warfarin). FUNDING: Intercept Pharmaceuticals, Inc.

Drug interaction profile of the HIV integrase inhibitor cabotegravir: assessment from in vitro studies and a clinical investigation with midazolam.

1. Cabotegravir (CAB; GSK1265744) is a potent HIV integrase inhibitor in clinical development as an oral lead-in tablet and long-acting injectable for the treatment and prevention of HIV infection. 2. This work investigated if CAB was a substrate for efflux transporters, the potential for CAB to interact with drug-metabolizing enzymes and transporters to cause clinical drug interactions, and the effect of CAB on the pharmacokinetics of midazolam, a CYP3A4 probe substrate, in humans. 3. CAB is a substrate for Pgp and BCRP; however, its high intrinsic membrane permeability limits the impact of these transporters on its intestinal absorption. 4. At clinically relevant concentrations, CAB did not inhibit or induce any of the CYP or UGT enzymes evaluated in vitro and had no effect on the clinical pharmacokinetics of midazolam. 5. CAB is an inhibitor of OAT1 (IC50 0.81 µM) and OAT3 (IC50 0.41 µM) but did not or only weakly inhibited Pgp, BCRP, MRP2, MRP4, MATE1, MATE2-K, OATP1B1, OATP1B3, OCT1, OCT2 or BSEP. 6. Based on regulatory guidelines and quantitative extrapolations, CAB has a low propensity to cause clinically significant drug interactions, except for coadministration with OAT1 or OAT3 substrates.

Clinical drug-drug interaction assessment of ivacaftor as a potential inhibitor of cytochrome P450 and P-glycoprotein.

Ivacaftor is approved in the USA for the treatment of cystic fibrosis (CF) in patients with a G551D-CFTR mutation or one of eight other CFTR mutations. A series of in vitro experiments conducted early in the development of ivacaftor indicated ivacaftor and metabolites may have the potential to inhibit cytochrome P450 (CYP) 2C8, CYP2C9, CYP3A, and CYP2D6, as well as P-glycoprotein (P-gp). Based on these results, a series of clinical drug-drug interaction (DDI) studies were conducted to evaluate the effect of ivacaftor on sensitive substrates of CYP2C8 (rosiglitazone), CYP3A (midazolam), CYP2D6 (desipramine), and P-gp (digoxin). In addition, a DDI study was conducted to evaluate the effect of ivacaftor on a combined oral contraceptive, as this is considered an important comedication in CF patients. The results indicate ivacaftor is a weak inhibitor of CYP3A and P-gp, but has no effect on CYP2C8 or CYP2D6. Ivacaftor caused non-clinically significant increases in ethinyl estradiol and norethisterone exposure. Based on these results, caution and appropriate monitoring are recommended when concomitant substrates of CYP2C9, CYP3A and/or P-gp are used during treatment with ivacaftor, particularly drugs with a narrow therapeutic index, such as warfarin.

Validation of 4ß-hydroxycholesterol and evaluation of other endogenous biomarkers for the assessment of CYP3A activity in healthy subjects.

AIMS: This study aimed to assess changes in the plasma concentrationss of 4ß-hydroxycholesterol (4ßHC) against intravenous (i.v.) and oral midazolam (MDZ) pharmacokinetics (PK) after administration of a potent CYP3A inhibitor [ketoconazole (KETO)] and inducer [rifampicin (RIF)]. METHODS: Thirty-two healthy subjects (HS) were allocated into three groups of 12 each in KETO and RIF and 10 in a placebo group (PLB). All HS were randomized to receive oral and i.v. MDZ on day 1 or 2 and on day 15 or 16 after receiving RIF (600 mg once daily), KETO (400 mg once daily) or PLB for 2 weeks. Subjects were followed until day 30. The effect of treatments on 4ßHC was assessed by analyzing % change from baseline using a linear spline mixed effects model. RESULTS: Compared with PLB, KETO decreased 4ßHC mean values up to 13% (P = 0.003) and RIF increased 4ßHC mean values up to 220% (P < 0.001). Within 14 days of stopping KETO and RIF, 4ßHC had either returned to baseline (KETO) or was still returning to baseline (RIF). Compared with baseline, mean oral MDZ AUC increased by 11-fold (90% CI ranging from 9-fold to 13-fold increase) and decreased by 92% (90% CI ranging from 90% to 95% decrease) after KETO and RIF, respectively. Similar trends were observed for 6ß-hydroxycortisol : cortisol (6ßHCL : CL) urinary ratios. CONCLUSIONS: Changes in plasma 4ßHC can be utilized as a surrogate for MDZ PK after multiple doses of potent CYP3A inducers. There is a more limited dynamic range for 4ßHC for assessment of potential CYP3A inhibitors. 4ßHC is a valuable tool for the assessment of potential CYP3A inducers in early drug development.

Geneva cocktail for cytochrome p450 and P-glycoprotein activity assessment using dried blood spots.

The suitability of the capillary dried blood spot (DBS) sampling method was assessed for simultaneous phenotyping of cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp) using a cocktail approach. Ten volunteers received an oral cocktail capsule containing low doses of the probes bupropion (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A), and fexofenadine (P-gp) with coffee/Coke (CYP1A2) on four occasions. They received the cocktail alone (session 1), and with the CYP inhibitors fluvoxamine and voriconazole (session 2) and quinidine (session 3). In session 4, subjects received the cocktail after a 7-day pretreatment with the inducer rifampicin. The concentrations of probes/metabolites were determined in DBS and plasma using a single liquid chromatography-tandem mass spectrometry method. The pharmacokinetic profiles of the drugs were comparable in DBS and plasma. Important modulation of CYP and P-gp activities was observed in the presence of inhibitors and the inducer. Minimally invasive one- and three-point (at 2, 3, and 6 h) DBS-sampling methods were found to reliably reflect CYP and P-gp activities at each session.

Assessment of the hepatic CYP reductase null mouse model and its potential application in drug discovery.

CYP Oxidoreductase (Por) is the essential electron donor for all CYP enzymes and is responsible for the activation of CYP. The Taconic Hepatic CYP Reductase Null (HRN) mouse model possesses a targeted mutation that results in liver-specific deletion of the Por gene thereby resulting in a disruption of CYP metabolism in the liver. The objectives of these studies were to further characterize the HRN mouse using probe drugs metabolized by CYP. In addition, tumor exposure in xenograft tumor bearing HRN immune-compromised (nude) mice was also determined. In HRN mice following intravenous (iv) administration of midazolam, clearance (CL) was reduced by ∼ 80% compared to wild-type mice (WT). After oral administration, the AUC of midazolam was increased by ∼ 20-fold in HRN mice compared to WT mice; this greater effect suggests that hepatic first pass plays a role in the oral CL of midazolam. A 50% and an 80% decrease in CL were also observed in HRN mice following iv administration of docetaxel and theophylline, respectively, compared to WT mice. In addition, a 2- to 3-fold increase in tumor concentrations of G4222, a tool compound, were observed in tumor bearing HRN nude mice compared to tumor bearing nude WT mice. The observations from these experiments demonstrate that, for compounds that are extensively metabolized by hepatic CYP, the HRN mouse model could potentially be valuable for evaluating in vivo efficacy of tool compounds in drug discovery where high hepatic CL and low exposure may prevent in vivo evaluation of a new chemical entity.