Drug-drug interactions related to hospital admissions in older adults: A prospective study of 1000 patients

OBJECTIVE: To investigate the frequency, nature, and side effects of drug-drug DESIGN: Study of drugs administered at home in the 2 weeks preceding hospitalization. SETTING: Evaluation of patients admitted to a geriatric unit from the emergency unit. PATIENTS: One thousand inpatients more than 70 years of age (83.0 +/- 7.1 years), admitted consecutively to a hospital for acute illness. MEASUREMENTS: All possible two by two combinations of drugs administered at home were considered to determine whether these associations could lead to a DDI and whether side effects resulted from these interactions. RESULTS: Five hundred thirty-eight patients were exposed to 1087 DDI. The most frequently involved drugs were cardiovascular and psychotropic medications. There were 189 side effects observed in 130 patients. The most frequent side effects were neuropsychological impairment, arterial hypotension, and acute renal failure. The number of side effects did not differ between the 66 contraindicated drug associations and the 1021 associations that only required precautionary use. CONCLUSIONS: DDI frequently lead to side effects in older adults. Classifications of DDI must be adapted to increased DDI sensitivity in this population. Nevertheless the frequency of side effects might be reduced by limiting the prescription of the most frequent and dangerous DDI.