Prosthetic heart valve thrombosis during dicloxacillin therapy.

A 76-year-old woman receiving warfarin after aortic valve replacement experienced prosthetic valve thrombosis during dicloxacillin therapy. Successful thrombolysis was achieved with tissue plasminogen activator. The international normalized ratio (INR) on admission was reduced to 1.4 and an increased warfarin dosage was required for three weeks following discontinuation of dicloxacillin treatment in order to maintain therapeutic INRs. Careful monitoring of INRs and titration of the warfarin dosage is recommended when dicloxacillin is prescribed to patients receiving warfarin.