<p>In vitro drug metabolism studies suggest that Rosiglitazone does not inhibit any of the major P450 enzymes at clinically relevant concentrations. A decrease in the dose of Rosiglitazone may be needed when gemfibrozil is introduced. Dosage adjustment is also required when administered with rifampin. Rosiglitazone was shown to have no clinically relevant effect on the pharmacokinetics of nifedipine and oral contraceptives.</p>