Drug interactions in patients on long-term oral anticoagulant and antihypertensive adrenergic neuron-blocking drugs.

The occurrence of drug interactions was studied in outpatients on anticoagulant or adrenergic neuron-blocking drugs. In the anticoagulant group (254 patients) a theoretical potential drug interaction with warfarin was noted in 33% of patients with drugs supplied by prescription and in 30% of patients with drugs taken as self-medication, though a probable adverse drug interaction was documented in only 9% of patients. The deficiency in the transfer of information about current drug therapy and the lack of awareness of patients about the hazards of anticoagulant therapy was clear.In the 64 patients on the adrenergic neuron-blocking drugs guanethidine, bethanidine, or debrisoquine a theoretical potential drug interaction was noted in 34%, but a probable adverse drug interaction was documented in only three patients. Further studies are required of other well-recognized groups of patients on drugs which are known to interact to assess the relevance and clinical importance of the formidable lists of interactions which are now available to doctors who prescribe drugs.