Epidemiology of drug exposure and adverse drug reactions in two Swiss departments of internal medicine

Aims To explore drug exposure, frequency of adverse drug reactions (ADRs), types of ADRs, predisposing risk factors and ADR-related excess hospital st ay in medical inpatients. Methods Structured data regarding patient characteristics, 'events' (sympto ms, laboratory results), diagnoses (ICD10) and drug therapy were collected using a computer-supported data entry system and an interface for data retr ieval from electronic patient records. ADR data were collected by 'event mo nitoring' to minimize possible bias by the drug monitor. The causality of e ach event was assessed in relation to disease(s) and drug therapy. Results The analysis included 4331 (100%) hospitalizations. The median obse rvation period was 8 days. The median number of different drugs administere d per patient and day was 6 and varied between 4 (Q(1)) and 9 (Q(3)) differ ent drugs in 50% of all hospital days. In 41% of all hospitalizations at le ast one disease-unrelated event could be possibly attributed to drug therap y. Clinically relevant ADRs occurred in 11% of all hospitalizations. In 3.3 % of all hospitalizations ADRs were the cause of hospital admission. The in cidence of possibly ADR-related deaths was 1.4 parts per thousand. Factors predisposing for clinically relevant ADRs were female gender and polypharma cy. ADR-related excess hospital stay accounted for 8.6% of hospital days. Conclusions These data demonstrate the feasibility of the developed 'event monitoring' system for quantitative analysis of ADRs in medical inpatients. With increasing numbers of recorded patients the pharmacoepidemiological d atabase provides a valuable tool to study specific questions regarding drug s efficacy and safety in hospitalized patients.