Abstract

Irreversible inhibition, characterized as mechanism-based inhibition (MBI), of cytochrome P450 in drugs has to be avoided for their safe use. A comprehensive assessment of drug-drug interaction (DDI) potential is important during the drug discovery process. In the present study, we evaluated the effects of macrolide antibiotics, erythromycin (ERM), clarithromycin (CAM), and azithromycin (AZM), which are mechanism-based inhibitors of CYP3A, on biotransformation of midazolam (MDZ) in monkeys. These macrolides inhibited the formation of 1′-hydroxymidazolam in monkey microsomes as functions of incubation time and macrolide concentration. Furthermore, the inactivation potentials of macrolides (k_inact/K_I: CAM ≅ ERM > AZM) were as effective as that observed in human samples. In in vivo studies, MDZ was administered orally (1 mg/kg) without or with multiple oral dosing of macrolides (15 mg/kg, twice a day on days 1–3). On day 3, the area under the plasma concentration-time curve (AUC) of MDZ increased 7.0-, 9.9-, and 2.0-fold with ERM, CAM, and AZM, respectively, compared with MDZ alone. Furthermore, the effects of ERM and CAM on the pharmacokinetics of MDZ were also observed on the day (day 4) after completion of macrolide treatments (AUC changes: 7.3- and 7.3-fold, respectively). Because the plasma concentrations of macrolides immediately before MDZ administration on day 4 were much lower than the IC₅₀ values for reversible CYP3A inhibition, the persistent effects may be predominantly caused by CYP3A inactivation. These results suggest that the monkey might be a suitable animal model to predict DDIs caused by MBI of CYP3A.