Adverse drug reactions: a cohort study in internal medicine units at a university hospital

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Abstract
Objectives Adverse drug reactions (ADRs) are important causes of hospitalization, morbidity and mortality in hospitalized patients. In addition to the impact they have on human life, they also significantly influence health costs. This study intended to (1) identify suspected ADRs and establish their frequency of development, (2) establish a causal relationship with the suspected drug(s) and (3) verify if there is an association between the development of an ADR and factors such as age, gender, number of diagnoses and number of prescribed medications. Methods This cohort study considered hospitalized patients at five inpatient internal medicine units in a university hospital located in southern Brazil. Patients were intensively monitored in order to identify suspected ADRs during hospitalization. The types of reactions were classified and a causal relationship was established using an algorithm. Results The cohort study followed 333 patients and approximately 43% of them presented at least one suspected ADR. Three hundred and sixty suspected ADRs were identified, with 19.7% manifesting before the patient was admitted and 80.3% during hospitalization. Medications that were most commonly involved in these suspected cases were anti-infectious agents followed by drugs that act on the central nervous system (CNS). The follow-up length and number of medications in use were independent risk factors for the development of an ADR. The same relationship was not observed for age, gender and number of diagnoses. Conclusion ADRs are a major problem in our setting and measures must be adopted to minimize them.