Background: Predisposition to adverse drug events with advancing age has led to the development of lists of potentially inappropriate medications (PIMs) to be avoided in the elderly, such as the Beers Criteria. The prevalence of Beers medications has been studied widely, but it is still unclear whether PIM use is predictive of adverse events in older people. Objectives: To examine potential associations between exposure to PIMs from the general Beers list and unplanned hospitalizations in elderly Western Australians. Methods: Using an enhanced case-time-control design and conditional logistic regression applied to the pharmaceutical claims and other linked health data of 251 305 Western Australians aged >= 65 years (1993-2005), odds ratios for unplanned hospitalization were obtained, from which attributable fractions, number and proportion of hospitalizations associated with drug exposure were derived. Results: Based on the health profiles of 383 150 hospitalized index subjects, overall PIM exposure was associated with an elevated risk of unplanned hospitalization (adjusted odds ratio = 1.18; 95% confidence interval = 1.15-1.21), this estimated risk increasing with the number of different PIMs and PIM quantity taken. Fifteen percent of unplanned hospitalizations in exposed index subjects (1980 per year) were attributed to PIM exposure. Patients taking meperidine (pethidine), nitrofurantoin, promethazine, indomethacin, and thioridazine appeared to be at particularly high risk of unplanned hospitalization, whereas temazepam, oxazepam, diazepam, digoxin, amiodarone, ferrous sulfate, and naproxen were attributed the greatest numbers of unplanned hospitalizations. Conclusions: Due caution prescribing Beers medications in the elderly seems justified, paying particular attention to PIMs listed above and to the concurrent use of multiple PIMs. Our results also support the retention of specific medications on PIM lists in future developments.
