PBPK perspective on alternative CYP3A4 inducers for rifampin

Identification of a Safe and Tolerable Carbamazepine Dosing Paradigm that Facilitates Effective Evaluation of CYP3A4 Induction

Carbamazepine (CBZ) is the recommended alternative to rifampicin as a CYP3A4 inducer in drug-drug interaction studies. However, the traditional CBZ dosing paradigm can lead to several adverse events (AEs). This study tested a shorter CBZ dosing regimen using the CYP3A4-sensitive index substrate midazolam (MDZ). This was a fixed-sequence arm of an open-label, phase I study (NCT04840888). Healthy participants (n = 15) aged 18-63 years received oral doses of 1.2 mg MDZ alone (Day 1), CBZ b.i.d. alone (100 mg Days 2-4; 200 mg Days 5-7; 300 mg Days 8-10 and 12-13), and 300 mg CBZ b.i.d. plus 1.2 mg MDZ (Days 11 and 14). One participant (6.7%) experienced constipation due to treatment with CBZ plus MDZ on Day 11. One participant (6.7%) experienced urticaria (Days 12-13), and two participants (13.3%) experienced somnolence (Days 8-10) due to treatment with 300 mg CBZ b.i.d. alone. All AEs were mild. For MDZ, the geometric mean (90% CI) ratio (vs. Day 1) of the area under the curve (AUC 0-∞) was 0.28 (0.24-0.31) on Day 11 and 0.26 (0.23-0.29) on Day 14. The AUC (0-12 hours) of CBZ was 114,000 ng∙h/mL on Day 11 and 105,000 ng∙h/mL on Day 14. Steady-state concentrations of CBZ and induction of CYP3A4 were achieved on Day 11. The data are consistent with predictions of physiologically-based pharmacokinetic models in Simcyp. The 9-day dosing regimen for CBZ induction was well-tolerated by healthy participants, supporting the use of a shorter CBZ regimen for CYP3A4 induction studies.

Effect of Carbamazepine on the Pharmacokinetics of Erdafitinib in Healthy Participants

Erdafitinib, a selective and potent oral pan-FGFR inhibitor, is metabolized mainly through CYP2C9 and CYP3A4 enzymes. This phase 1, open-label, single-sequence, drug-drug interaction study evaluated the pharmacokinetics, safety, and tolerability of a single oral dose of erdafitinib alone and when co-administered with steady state oral carbamazepine, a dual inducer of CYP3A4 and CYP2C9, in 13 healthy adult participants (NCT04330248). Compared with erdafitinib administration alone, carbamazepine co-administration decreased total and free maximum plasma concentrations of erdafitinib (Cmax) by 35% (95% CI 30%-39%) and 22% (95% CI 17%-27%), respectively. The areas under the concentration-time curve over the time interval from 0 to 168 hours, to the last quantifiable data point, and to time infinity (AUC168h, AUClast, AUCinf), were markedly decreased for both total erdafitinib (56%-62%) and free erdafitinib (48%-55%). The safety profile of erdafitinib was consistent with previous clinical studies in healthy participants, with no new safety concerns when administered with or without carbamazepine. Co-administration with carbamazepine may reduce the activity of erdafitinib due to reduced exposure. Concomitant use of strong CYP3A4 inducers with erdafitinib should be avoided.

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.

Pharmacokinetics of asundexian with combined CYP3A and P-gp inhibitors and an inducer: Target in vitro and in vivo studies

AIMS

Asundexian is an oral, direct and reversible inhibitor of activated factor XI (FXIa) in development for the treatment of thromboembolic events. This article summarizes results from preclinical and clinical studies, including identification of enzymes involved in asundexian pharmacokinetics, and evaluation of potential target drug-drug interactions.

METHODS

In vitro studies investigated the substrate characteristics of asundexian towards several cytochrome P450 (CYP) isoforms, hydrolytic enzymes and drug transporters. Inhibition of the amide hydrolysis of asundexian was investigated in vitro for several relevant drugs. Phase 1 studies in healthy male participants investigated the pharmacokinetics (PK) of asundexian upon co-administration of combined inhibitors or an inducer of P-gp and CYP3A4 (itraconazole, verapamil or carbamazepine, respectively, or the moderate CYP3A4 inhibitor fluconazole). The pharmacodynamic (PD) markers are activated partial thromboplastin time and FXIa inhibition.

RESULTS

Asundexian was predominantly metabolized via carboxylesterase 1 and, to a lesser extent, via CYP3A4 and is a substrate of P-gp. The asundexian area under the plasma concentration-time curve (AUC) increased by 103% and 75.6% upon combined inhibition of P-gp and strong or moderate inhibition of CYP3A4, respectively, but was unaffected by moderate CYP3A4 inhibition. Combined P-gp and CYP3A4 induction by carbamazepine decreased asundexian AUC by 44.4%. PD is concentration-dependent, thus no differences in maximum responses and recovery commensurate with PK effect(s) were observed. Adverse events were mild and asundexian was well tolerated.

CONCLUSIONS

The presented studies confirmed that CYP3A4 and P-gp contribute to asundexian metabolism and excretion. Observed effects were in line with data from a previous mass balance study.

The Impact of N-nitrosamine Impurities on Clinical Drug Development

Over the past few years, an increasing number of commercially available drugs have been reported to contain N-nitrosamine impurities above acceptable intake limits. Consequent interruption or discontinuation of the manufacturing and distribution of several marketed drugs has culminated into shortages of marketed drugs, including the antidiabetic drug metformin and the potentially life-saving drug rifampin for the treatment of tuberculosis. Alarmingly, the clinical development of new investigational products has been complicated as well by the presence of N-nitrosamine impurities in batches of marketed drug. In particular, rifampin is a key clinical index drug employed in drug-drug interaction (DDI) studies, and as a result of nitrosamine impurities regulatory bodies no longer accept the administration of rifampin in DDI studies involving healthy subjects. Drug developers are now forced to look at alternative approaches for commonly employed perpetrators, which will be discussed in this review.