CIMETIDINE: INTERACTION WITH ORAL ANTICOAGULANTS IN MAN

In 6 patients anticoagulated with warfarin, nicoumalone, or phenindione the addition of cimetidine prolonged the prothrombin-time (PT) by a mean of 12·6 s (range 5-23 s). In 7 volunteers taking daily subtherapeutic doses of warfarin the addition of cimetidine increased the PT from 19·4 to 22·9 s and the plasma-warfarin concentration from 0·96 to 1·76 μg/ml. Cimetidine reduced the single-dose clearance of warfarin and antipyrine. The basis of the interaction between cimetidine and oral anticoagulants is probably inhibition of drug metabolism. Care should be exercised in concomitant therapy.