Evaluation of dilution, dialysis and ultracentrifugation methods to assess the reversibility of metabolism-dependent inhibitors (MDIs) of cytochrome P450 (CYP) enzymes
Metabolism-dependent inhibition (MDI) of P450 enzymes is a well-recognized cause of clinically significant drug-drug interactions (DDI). For this reason, the US Food & Drug Administration (FDA) and the European Medicines Agency (EMA) have both published draft guidance documents on DDI that require an in vitro assesment of the ability of drug candidates to cause MDI of the major drug-metabolizing P450 enzymes (2006, 2010). The most recent PhRMA publication and EMA draft guidance discuss in vitro experiments, to not only identify the potential for a drug candidate to cause MDI. (e.g. IC50 shift experiments), but also to evaluate whether MDI involves reversible or irreversible inhibition (Grimm et al., 2009).