Adverse drug reactions in an elderly outpatient population.

The prevalence of adverse drug reactions (ADRs) in elderly outpatients was investigated, along with factors that might be associated with their occurrence. The medical records of elderly patients attending an interdisciplinary geriatric clinic and a general medical clinic during 1988 were audited to collect a variety of demographic and treatment data and to detect documentation of first-time ADRs. Subjects were classified as having had an ADR if a physician documented this or if a relevant symptom was noted in the record and a score of 1 or above was obtained on the Adverse Drug Reaction Probability Scale. The presence of potential drug interactions was also assessed. The sample size was 463 patients, of whom 332 attended the medical clinic and 131 attended the geriatric clinic. Potential drug interactions were identified in the records of 143 subjects (31%). There were 107 documented ADRs in 97 patients (21%). Of these patients, 86 were noted by the physicians as having had an ADR. Twelve patients were hospitalized as a direct result of an ADR. Significant risk factors for ADRs were attendance in the geriatric clinic, the use of potentially harmful drug combinations, and the use of drugs that require therapeutic monitoring. Patient age and the number of drugs had no association with ADRs. In the elderly population studied, patients with frailty arising from multiple pathologies were more likely to have ADRs than the more robust elderly, even when their therapeutic regimens were simplified.