标题：Evidence for Time-Dependent Interactions between Ritonavir and Lopinavir/Ritonavir Plasma Levels Following P-Glycoprotein Inhibition in Sprague-Dawley Rats
摘要：The interaction between verapamil, a P-glycoprotein (P-gp) inhibitor, with ritonavir and lopinavir/ritonavir (LPV/r) after acute and chronic treatment was investigated in rats. Rats were divided into 4 groups, viz. Group 1: ritonavir, 20 mg/kg/d ( n =18), group 2: ritonavir, 20 mg/kg/d plus verapamil 5 mg/kg/d ( n =18), group 3: LPV/r, 80 and 20 mg/kg/d ( n =17) and group 4: LPV/r, 80 and 20 mg/kg/d plus verapamil 5 mg/kg/d ( n =18). Blood samples were collected after decapitation on days 1, 7 and 21. Lopinavir and ritonavir plasma levels were simultaneous determined by a validated LC/MS/MS method. The lower limit of quantification for both ritonavir and lopinavir was 0.078 μg/ml. Verapamil significantly increased ritonavir plasma levels, administered as monotherapy, following acute ( p <0.005) and chronic treatment (day 21) ( p <0.005). During acute (but not chronic) LPV/r treatment, verapamil also increased the lopinavir levels ( p <0.05). A time or exposure dependent pharmacokinetic interaction was thus observed between verapamil and ritonavir whether administered alone or after the lopinavir-ritonavir combination (LPV/r). This interaction occurred most prominently after acute treatment, and became less pronounced over time. This study indicates the importance of a longer time frame to investigate enzyme based drug interactions in rat models.
