Documenting drug-drug interactions in ambulatory patients

Abstract

Medical record review, patient interviews and laboratory test evaluations were used to determine the number, type and clinical significance of drug-drug interactions occurring in an ambulatory patient population. Medical records of 662 outpatients at a general medicine clinic of a teaching hospital were reviewed over a two-month period. Drug therapy was checked for any interactions listed in a textbook of drug interactions. Thirty-six patients (monitored group) whose drug therapy included a potential drug interaction of clinical significance were interviewed for medical history, symptoms and concurrent nonprescription drug use. Potential drug interactions in this group were confirmed by physical examination or diagnostic laboratory test results, or both. Potential drug interactions were identified in 24.2% (160) of patients. Only eight patients potentially had an interaction of major clinical significance; in each case, the interaction was tetracycline-antacid. Circulatory (94.4%) and endocrine (58.3%) disorders were the disorders observed most frequently in the monitored group which had an average of 1.5 potential interactions per patient. Potential interactions noted most frequently in the monitored group were digoxin-hydrochlorothiazide (61.7%) and digitalis preparations-potassium-depleting diuretics (91.7%). Fifteen patients in the monitored group were consuming a nonprescription drug that could potentially cause an interaction. Although 31 patients in the monitored group reported symptoms indicative of interaction, only two had both confirmatory laboratory test results and supportive clinical symptoms, giving an actual drug-drug interaction rate of 0.3% (2/662). Although the incidence of potential drug interactions was high, the actual occurrence of drug interactions was much lower. Patients with the highest risk of interaction were those with circulatory or endocrine disorders. The study methods were effective in detecting drug-drug interactions.