Inhibition of phenprocoumon anticoagulation by carbamazepine

Carbamazepine inhibits warfarin and dicoumarol anticoagulation through indu ction of cytochrome P450-enzymes. Inhibition phenprocoumon anticoagulation by carbamazepine has been supposed in some reviews, however, without hard e mpirical evidence. We report a patient who was anticoagulated with phenproc oumon in whom carbamazepine produced a dramatic increase in prothrombin tim e ratio (Quick). After discontinuation of carbamazepine, Quick-values retur ned to therapeutic levels. Valproate did not affect phenprocoumol's anticoa gulant properties. The potentially hazardous carbamazepine-phenprocoumon in teraction should be emphasized in reference drug manuals. (C) 2000 Elsevier Science B.V. All rights reserved.