Adverse drug reactions as cause of hospital admissions: results from the Italian Group of Pharmacoepidemiology in the Elderly (GIFA).

To determine the prevalence of adverse drug reaction (ADR)-related hospital admissions in an older population, to describe the most common clinical manifestations and drugs most frequently responsible for ADR-related hospital admissions, and to identify independent factors predictive of these ADRs. Multicenter pharmacoepidemiology survey conducted between 1988 and 1997. Eighty-one academic hospitals throughout Italy. Twenty-eight thousand four hundred eleven patients consecutively admitted to participating centers during the survey periods. For each suspected ADR at admission, a physician, who coded description, severity, and potentially responsible drugs, completed a questionnaire. Mean age +/- standard deviation of the patients was 70 +/- 16. One thousand seven hundred four ADRs were identified upon hospital admission. In 964 cases (3.4% of all admissions), ADRs were considered to be the cause of these hospital admissions. Of these, 187 ADRs were coded as severe. Gastrointestinal complaints (19%) represented the most common events, followed by metabolic and hemorrhagic complications (9%). The drugs most frequently responsible for these ADRs were diuretics, calcium channel blockers, nonsteroidal antiinflammatory drugs, and digoxin. Female sex (odds ratio (OR) = 1.30, 95% confidence interval (CI) = 1.10-1.54), alcohol use (OR = 1.39, 95% CI = 1.20-1.60), and number of drugs (OR = 1.24, 95% CI = 1.20-1.27 for each drug increase) were independent predictors of ADR-related hospital admissions. For severe ADRs, age (OR = 1.50, 95% CI = 1.01-2.23 for age 65-79 and OR = 1.53, 95% CI = 1.00-2.33 for age > or =80, respectively), comorbidity (OR = 1.12, 95% CI = 1.05-1.20 for each point in the Charlson Comorbidity Index), and number of drugs (OR = 1.18, 95% CI = 1.11-1.25 for each drug increase) were the only predisposing factors. The most important determinant of risk for ADR-related hospital admissions in older patients is number of drugs being taken. When considering only severe ADRs, risk is also related to age and frailty.