The complexity of achieving anticoagulation control in the face of warfarin-phenytoin interaction: an Asian case report.
Phenytoin has been reported to have major interactions with warfarin. Phenytoin induces warfarin's metabolism. However, there are many case reports which provide conflicting conclusions. Here, we report a case of a 65-year-old man with mechanical heart valve on chronic warfarin therapy who experienced persistent fluctuations of INR and bleeding secondary to probable warfarin-phenytoin interactions. The patient's anticoagulation clinic visits prior to hospitalization were thoroughly evaluated and we continued to follow-up the case for 3 months post-hospitalization. The reported interaction could be reasonably explained from the chronology of events and the pattern of INR fluctuations whenever phenytoin was either added or discontinued from his drug regimen.
Hassan
Yahaya
Y
Department of Clinical Pharmacy, School of Pharmaceutical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia. yahaya@usm.my
Awaisu
Ahmed
A
Aziz
Noorizan Abd
NA
Ismail
Omar
O
D000368:Aged; D000925:Anticoagulants / Q000493:pharmacokinetics* / Q000627:therapeutic use; D000927:Anticonvulsants / Q000009:adverse effects* / Q000627:therapeutic use; D004357:Drug Synergism; D006350:Heart Valve Prosthesis; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D010672:Phenytoin / Q000009:adverse effects* / Q000627:therapeutic use; D012640:Seizures / Q000188:drug therapy; D014859:Warfarin / Q000493:pharmacokinetics* / Q000627:therapeutic use
D000925:Anticoagulants; D000927:Anticonvulsants; D014859:Warfarin; D010672:Phenytoin