Polypharmacy as a risk factor for adverse drug reactions in geriatric nursing home residents.

OBJECTIVE Polypharmacy is a well-known risk factor for adverse drug reactions (ADRs). The objective of this study was to determine the relationship between the use of > or = 9 different scheduled medications and the occurrence of ADRs in geriatric nursing home residents. METHODS This was a retrospective cohort study conducted in a 1200-bed, county-owned and -operated, longterm care skilled nursing facility Participants were 335 subjects aged > or = 65 years who were present at the facility during the index month of October 1998. Hospice, respite care, and rehabilitation patients were excluded. Use of > or = 9 different scheduled medications was defined a priori as routinely administered medications, excluding as-needed agents, topical agents, 1-time administration, and vaccinations. ADRs were identified by voluntary reporting and by chart review during a 12-month period. ADRs were assessed individually by 2 clinical pharmacists applying the Naranjo ADR probability scale. RESULTS A total of 207 ADRs were identified. The cohort receiving > or = 9 scheduled medications (n = 43) experienced 53 ADRs, compared with 154 ADRs in the control group receiving <9 medications (n = 292). The demographic distribution was similar in both cohorts, with white as the dominant ethnicity; 45% were white in the control group and 51% were white in the cohort group receiving > or = 9 scheduled medications. The sex distribution was also similar, with women outnumbering men in both cohorts: 60% and 81% were women in the control and cohort groups, respectively. The mean age was 72 years (range, 65-100 years). After the data were adjusted for the number of days each subject was at risk for experiencing an ADR, subjects using > or = 9 different scheduled medications were 2.33 times more likely than controls to experience an ADR (95% CI, 1.54-3.52; P < 0.001). CONCLUSION A positive correlation between the use of >/=9 different scheduled medications and ADRs was found among these geriatric nursing home residents.

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