Effects of ketoconazole and esomeprazole on the pharmacokinetics of pazopanib in patients with solid tumors

The metabolism of pazopanib is primarily mediated by CYP3A4. The solubility of pazopanib is pH-dependent, and an elevated gastric pH may decrease its bioavailability. This study evaluated the effect of a potent CYP3A4 inhibitor, ketoconazole, and the proton pump inhibitor esomeprazole on the pharmacokinetics and safety of pazopanib and its metabolites. In Arm A, patients received pazopanib 400 mg alone once daily for 7 days followed by pazopanib 400 mg plus ketoconazole 400 mg once daily for 5 days. In Arm B, patients received pazopanib 800 mg once daily for 7 days, followed by pazopanib 800 mg plus esomeprazole 40 mg once daily for 5 days, and then pazopanib alone on the last day. Arm A enrolled 21 patients. In the presence of ketoconazole, mean area under the plasma concentration-time curve 24 h post-dose (AUC((0-24))) and mean maximum observed concentration (C (max)) of pazopanib increased by 66 and 45 %, respectively; mean AUC((0-24)) and C (max) for pazopanib metabolites were lower or remained unchanged. Arm B enrolled 13 patients. In the presence of esomeprazole, mean pazopanib AUC((0-24)) and C (max) decreased by 40 and 42 %, respectively; mean values of those parameters for metabolites of pazopanib also decreased. Concomitant use of pazopanib with a strong CYP3A4 inhibitor should be avoided. If coadministration is necessary, pazopanib should be reduced to 400 mg. Concomitant use of pazopanib and proton pump inhibitors should also be avoided. Alternative dosing regimens that do not increase gastric pH at the time of pazopanib dosing should be considered.