Adverse Drug Reactions as Cause of Hospital Admissions: Results from the Italian Group of Pharmacoepidemiology in the Elderly (GIFA)

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Abstract
OBJECTIVES: 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.DESIGN: Multicenter pharmacoepidemiology survey conducted between 1988 and 1997.SETTING: Eighty‐one academic hospitals throughout Italy.PARTICIPANTS: Twenty‐eight thousand four hundred eleven patients consecutively admitted to participating centers during the survey periods.MEASUREMENTS: For each suspected ADR at admission, a physician, who coded description, severity, and potentially responsible drugs, completed a questionnaire.RESULTS: 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 ≥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.CONCLUSIONS: 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.