The burden and risk factors for adverse drug events in older patients - a prospective cross-sectional study

Objective. To determine the burden and risk factors for adverse drug events (ADEs) in older patients. Design. A prospective cross-sectional study. Methods. Patients (65 years and older) presenting to the tertiary Emergency Unit of Groote Schuur Hospital, Cape Town, between February and May 2005, were assessed for well-established ADEs, as defined by the South African Medicines Formulary. Logistic regression models were fitted to determine drugs and other factors associated with the likelihood of developing ADEs. Results. ADEs were identified in 104 of the 517 (20%) presentations. The most frequently involved drug classes were cardiovascular (34%), anticoagulant (27%), analgesic (19%) and antidiabetic (9%). Patients who developed ADEs were more likely to have five or more prescription drugs (p < 0.0001), more than three clinical problems (p = 0.001)., require admission (p = 0.04), and report compliance with medication (p = 0.02) than those who did not. Drugs shown to independently confer increased risk of ADEs were angiotensin-converting enzyme inhibitors (RR = 2.6, 95% CI: 1.3 - 5.2, p = 0.009), non-steroidal anti-inflammatory drugs (RR = 4.1, 95% CI: 2.1 - 8.0, p < 0.0001) and warfarin (RR = 3.1, 95% CI: 1.6 - 6.3, p = 0.0014). Conclusion. ADEs contribute significantly to the burden of elderly care in the Emergency Unit. In a setting such as ours, increased pill burden and certain drug classes are likely to result in increased risk of ADEs in the older population group.