Drug Interactions between amoxicillin / clarithromycin / omeprazole and axitinib

GENERALLY AVOID: Coadministration with potent inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of axitinib, which is primarily metabolized by the isoenzyme. In 32 healthy volunteers, administration of a single 5 mg dose of axitinib on day 4 of treatment with the potent CYP450 3A4 inhibitor ketoconazole (400 mg/day for 7 days) resulted in a 1.5-fold increase in mean axitinib peak plasma concentration (Cmax) and 2-fold increase in mean systemic exposure (AUC) compared to administration of axitinib alone. The mean plasma half-life of axitinib also increased from 9.4 hours when given alone to 13.1 hours in the presence of ketoconazole. The combination was well tolerated by study subjects. Most treatment-related adverse events were mild in severity, with headache and nausea reported most frequently. No clinically significant effects on blood pressure were observed for single-dose axitinib plus ketoconazole relative to axitinib alone.

MANAGEMENT: Concomitant use of axitinib with potent CYP450 3A4 inhibitors should generally be avoided. Some authorities recommend avoiding concomitant use of axitinib during and for 2 weeks after treatment with itraconazole. Alternative agents with no or minimal CYP450 3A4 inhibition potential are recommended whenever possible. Should concomitant treatment with a potent inhibitor be required, the manufacturer recommends that axitinib dosage be reduced by approximately one-half, as this is predicted to adjust the axitinib systemic exposure (AUC) to the range observed without inhibitors; however, clinical data are lacking. Subsequent dosage adjustments can be made according to individual therapeutic response and tolerability. Following discontinuation of the potent CYP450 3A4 inhibitor, the axitinib dosage should be returned (after 3 to 5 half-lives of the inhibitor) to that used prior to initiation of the inhibitor.

Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.

Clarithromycin may increase and prolong the omeprazole plasma concentration. The mechanism may be related to clarithromycin inhibition of hepatic cytochrome P450 enzymes responsible for omeprazole metabolism. Coadministration of omeprazole may result in an increase in clarithromycin and 14-(R)-hydroxyclarithromycin plasma concentrations. These increases may be due to the effect of omeprazole on gastric pH.

Since the aqueous solubility of axitinib is pH-dependent, with higher pH resulting in lower solubility, drugs that increase the pH of the upper gastrointestinal tract may reduce the oral bioavailability of axitinib. The interaction has been studied with rabeprazole. When given with rabeprazole (20 mg once daily for 5 days), axitinib peak plasma concentration (Cmax) and systemic exposure (AUC) decreased by approximately 50% and 20%, respectively. These changes are not considered clinically significant. No dosage adjustment for axitinib is recommended during coadministration with proton pump inhibitors, H2-receptor antagonists, or antacids.