** Thanks for contacting HCM with your health concern 1. Coumadin [warfarin] is a potent anticoagulant which interferes with vitamin K dependent clotting factors and thus bleeding is a major complication of the drug and antimicrobial drugs can increase the anti coagulant effect of warfarin and ciprofloxacin [flouoroquinolone] is one of them so regular blood investigations should be carried out like bleeding time [BT], clotting time [CT], prothrombin time [PT], and International normalised ratio [INR] 2. although the drug interaction does not occur routinely but case has been reported where there was fatal intracerebral hemorrhage in an old man while taking ciprofloxacin and warfarin. PS. Since effect of antibiotic on any individual cannot be predicted thus anyone taking the said combination[s] should be under regular supervision and guidance of health care professional.