Altered irinotecan metabolism in a patient receiving phenytoin

The systemic exposure to the anticancer agent irinotecan (CPT-11) and its active metabolite SN-38 were 79 and 92% reduced, respectively, relative to literature data, by concomitant phenytoin therapy. This finding suggests that increased doses of CPT-11 should be given to patients treated simultaneously with these drugs, to achieve adequate levels of SN-38.