Impact of Tesamorelin, a Growth Hormone-Releasing Factor (GRF) Analogue, on the Pharmacokinetics of Simvastatin and Ritonavir in Healthy Volunteers

A Mechanistic Absorption and Disposition Model of Ritonavir to Predict Exposure and Drug-Drug Interaction Potential of CYP3A4/5 and CYP2D6 Substrates

BACKGROUND AND OBJECTIVES

Due to health authority warnings and the recommended limited use of ketoconazole as a model inhibitor of cytochrome P450 (CYP) 3A4 in clinical drug-drug interaction (DDI) studies, there is a need to search for alternatives. Ritonavir is a strong inhibitor for CYP3A4/5-mediated DDIs and has been proposed as a suitable alternative to ketoconazole. It can also be used as a weak inhibitor for CYP2D6-mediated DDIs. Most of the currently available physiologically based pharmacokinetic (PBPK) inhibitor models developed for predicting DDIs use first-order absorption models, which do not mechanistically capture the effect of formulations on the systemic exposure of the inhibitor. Thus, the main purpose of the current study was to verify the predictive performance of a mechanistic absorption and disposition model of ritonavir when it was applied to the inhibition of CYP2D6 and CYP3A4/5 by ritonavir.

METHODS

A PBPK model that incorporates formulation characteristics and enzyme kinetic parameters for post-absorptive pharmacokinetic processes of ritonavir was constructed. Key absorption-related parameters in the model were determined using mechanistic modelling of in vitro biopharmaceutics experiments. The model was verified for systemic exposure and DDI risk assessment using clinical observations from 13 and 18 studies, respectively.

RESULTS

Maximal inhibition of hepatic (3.53% of the activity remaining) and gut (5.16% of the activity remaining) CYP3A4 activity was observed when ritonavir was orally administered in doses of 100 mg or higher. The PBPK model accurately described the concentrations of ritonavir in the different simulated studies. The prediction accuracy for maximum concentration (C_max) and area under the plasma concentration versus time curve (AUC) were assessed. The bias (average fold error, AFE) for the prediction of C_max and AUC was 0.92 and 1.06, respectively, and the precision (absolute average fold error, AAFE) was 1.29 and 1.23, respectively. The PBPK model predictions for all C_max and AUC ratios when ritonavir was used as an inhibitor of CYP metabolism fell within twofold of the clinical observations. The prediction accuracy for C_max and AUC ratios had a bias (AFE) of 0.85 and 0.99, respectively, and a precision (AAFE) of 1.21 and 1.33, respectively.

CONCLUSIONS

The current model, which incorporates formulation characteristics and mechanistic disposition parameters, can be used to assess the DDI potential of CYP3A4/5 and CYP2D6 substrates administered with a twice-daily dose of 100 mg of ritonavir for 14 days.

New Drugs for NASH and HIV Infection: Great Expectations for a Great Need

In recent years, there has been an increasing number of clinical trials for the treatment of nonalcoholic steatohepatitis (NASH). People living with human immunodeficiency virus (PLWH) are commonly excluded from these studies, usually due to concerns over drug-drug interactions associated with antiretroviral therapy. The Steatohepatitis in HIV Emerging Research Network, a group of international experts in hepatology and infectious diseases, discusses our current understanding on the interaction between human immunodeficiency virus and NASH, and the issues related to the inclusion of PLWH in NASH clinical trials. Recent trials addressing NASH treatment in PLWH are discussed. The risk of drug-drug interactions between antiretroviral therapy and aramchol, cenicriviroc, elafibranor, obeticholic acid and resmetirom (MGL-3196), which are currently in phase 3 trials for the treatment of NASH, are reviewed. A model for trial design to include PLWH is proposed, strongly advocating for the scientific community to include this group as a subpopulation within studies.