Inhibition of CYP3A by Antimalarial Piperaquine and Its Metabolites in Human Liver Microsomes With IVIV Extrapolation

The potential of the antimalarial piperaquine and its metabolites to inhibit CYP3A was investigated in pooled human liver microsomes. CYP3A activity was measured by liquid chromatography-tandem mass spectrometry as the rate of 1′-hydroxymidazolam formation. Piperaquine was found to be a reversible, potent inhibitor of CYP3A with the following parameter estimates (%CV): IC₅₀ = 0.76 μM (29), K_i = 0.68 μM (29). In addition, piperaquine acted as a time-dependent inhibitor with IC₅₀ declining to 0.32 μM (28) during 30-min pre-incubation. Time-dependent inhibitor estimates were k_inact = 0.024 min^?1 (30) and K_I = 1.63 μM (17). Metabolite M2 was a highly potent reversible inhibitor with estimated IC₅₀ and K_i values of 0.057 μM (17) and 0.043 μM (3), respectively. M1 and M5 metabolites did not show any inhibitory properties within the limits of assay used. Average (95th percentile) simulated in vivo areas under the curve of midazolam increased 2.2-fold (3.7-fold) on the third which is the last day of piperaquine dosing, whereas for its metabolite M2, areas under the curve of midazolam increased 7.7-fold (13-fold).