- Taking a medication known to be a clinically significant cytochrome (CYP) 3A4 strong inhibitor (eg, ketoconazole within 14 days) or strong inducers (eg, rifampin and St. John's Wort within 14 days) of starting treatment with Oratecan. http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteracti onsLabeling/ucm080499.htm