RESUMEN
Background: Despite the importance of notifying and preventing adverse drug reactions (ADRs), they are under reported and their consequences are not adequately evaluated. Aim: To assess the impact of a pharmacovigilance system carried out by a pharmacist. Material and Methods: In an internal medicine service, the spontaneous report of ADRs was compared blindly with an active pharmacovigilance system in which a pharmacist detected, monitored and prevented ADRs. Results: A total of 1,196 patients was included. Of these 604 were hospitalized in intervened wards, where 50 suspected ADRs in 47 patients were reported. In non-intervened wards, only three ADRs were spontaneously reported. Therefore, the pharmacovigilance system significantly improved the detection and report of ADRs with a risk ratio of 15.4 (95% confidence intervals 4.8-49.1). Sixty six percent of ADRs were classified as severe. Antimicrobials were the main group of medications causing ADRs in 44% of reports. Forty three percent of ADRs were preventable and prolonged hospital stay by a mean of eight days. Conclusions: An active pharmacovigilance system carried out by pharmacists improves the detection of ADRs and promotes its prevention.