Objectives: This study was designed to assess the prevalence of adverse drug reactions (ADRs) in the internal medicine wards of two teaching hospitals, identify the most common ADRs, the principal medications involved, and determine the risk factors implicated in the occurrence of such ADRs.
Methods: All admissions over 10 weeks were followed prospectively using an intensive drug surveillance method to identify ADRs. Clinical laboratory data, the drug prescribed, and ADRs were taken into consideration. Status of nutrition, liver and kidney function at admission, and ADR time were determined. In order to assess drug interactions a software package was used.
Results: A total of 405 patients were evaluated, 126 patients (31%) had 128 ADRs, 122 ADRs occurred during hospitalization. Two ADR-related deaths were observed during the study. Reactions affecting the gastrointestinal tract, skin, and hematological system were among the most frequent ADRs. For ADRs observed during admission predictors of its occurrence in a multivariate regression model were: OR (95% CI); more than 12 days' hospitalization: 2.11(1.27-3.47), any drug interaction: 9.33 (5.12-17) and acute change in estimated glomerular filtration rate over admission >20%: 2.46 (1.45-4.2). Worsening of renal function or drug interaction was observed in nine of the ten ADRs. Age, sex, nutrition, and number of drugs used were not related to ADRs.
Conclusion: A significant prevalence of ADRs was found among hospitalized patients. Duration of hospital admission, changes in renal status during hospitalization and drug interactions seem to be important risk factors for ADRs.