RESUMEN
Background: it is not clear if old age is a risk factor for adverse drug reactions. Aim: to study the incidence of adverse drug reactions and the effect of age n patients admitted to and Internal Medicine Service in an university hospital. Patients and methods: two hundred one patients, hospitalized at the Clinical Hospital of the Catholic University, were studied. These patients were followed using a prospective pharmacological surveillance method. For statistical purposes patients aged 65 years old or older were compared with those younger than 65 years old. Results: patients over 65 years old bad a 33 percent incidence of adverse drug reactions, mainly involving cardiovascular system and provoking metabolic disturbances. Younger subyects bad a 24 percent incidence of adverse drug reactions, mainly involving the gastrointestinal system and the skin. Sixteen percent of adverse drug reactions were classified as severe and the was a direct relationship between its frequency and the number of drugs prescribed, the hospitalization length and the presence of renal failure. Younger patients with adverse drug reactions bad lower serum albumin levels than those without adverse reactions. This relationship was not observed in older patients. Conclusions: the frequency of adverse drug reactions in hospitalized patients, is related to the number of drugs prescribed and the lengib of hospitalization