Prevalence of adverse drug events in ambulatory care: a systematic review

Most medications are prescribed, dispensed, and administered in ambulatory care settings, yet little information exists on the adverse effects of drugs in this setting. This review was conducted to estimate the prevalence of adverse drug events (ADEs) and the proportion of preventable ADEs in ambulatory care settings; compare data for different age groups including children, adults, and elderly patients; and review drug classes most commonly associated with ADEs.

Four electronic databases-PubMed (1966-March 2011), International Pharmaceutical Abstracts (1970-March 2011), EMBASE (1980-March 2011), and the Cochrane Database of Systematic Reviews (1993-March 2011)-were systematically searched for published data. Bibliographies of retrieved articles were searched individually for additional relevant studies.

A standardized definition of an ADE was used to select studies in populations living in the community, with medical visits to primary care facilities, nonspecialty ambulatory care facilities, and/or admissions to a hospital for medication-related adverse events.

Data were extracted using a standardized table. Forty-three studies met our inclusion criteria.

The median ADE prevalence rate for retrospective studies was 3.3% (interquartile range [IQR] 2.3-7.1%) vs 9.65% (IQR 3.3-17.35%) for prospective studies. Median preventable ADE rates in ambulatory care-based studies were 16.5%, and 52.9% for hospital-based studies. Median prevalence rates by age group ranged from 2.45% for children to 5.27% for adults, 16.1% for elderly patients, and 3.45% for studies including all ages.

Despite a recent increase in publications on ADEs in the ambulatory care setting, most studies remain hospital based. Notable differences in prevalence rates by age groups and by responsible drug categories provide guidance on how to direct attention toward effective targets for improvement of medication safety in ambulatory care settings.