Drug Interactions between irinotecan and telithromycin

GENERALLY AVOID: Coadministration with potent inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of irinotecan and its active metabolite, SN-38. CYP450 3A4 is the isoenzyme responsible for the metabolic conversion of irinotecan to its inactive metabolite, APC. Inhibition of APC formation results in more irinotecan metabolism to SN-38, an active and toxic metabolite. High plasma levels of irinotecan and SN-38 may increase the risk of potentially fatal toxicities such as severe diarrhea, neutropenia, sepsis, and thromboembolism. In cancer patients, coadministration of ketoconazole, a potent CYP450 3A4 inhibitor, resulted in a 100% increase in the relative exposure to SN-38 and an 87% reduction in the exposure to APC. In HIV patients with Kaposi's sarcoma, coadministration of irinotecan with lopinavir-ritonavir decreased the clearance of irinotecan by 47%, increased the AUC of SN-38 by 204%, and decreased the AUC of APC by 81%.

MANAGEMENT: Concomitant use of irinotecan with potent CYP450 3A4 inhibitors should generally be avoided. Potent CYP450 3A4 inhibitors should be discontinued for at least one week before initiation of treatment with irinotecan.