Incidence and costs of adverse drug reactions during hospitalisation: computerised monitoring versus stimulated spontaneous reporting.

To implement a computer-based adverse drug reaction monitoring system and compare its results with those of stimulated spontaneous reporting, and to assess the excess lengths of stay and costs of patients with verified adverse drug reactions. A prospective cohort study was used to assess the efficacy of computer-based monitoring, and case-matching was used to assess excess length of stay and costs. This was a study of all patients admitted to a medical ward of a university hospital in Germany between June and December 1997. 379 patients were included, most of whom had infectious, gastrointestinal or liver diseases, or sleep apnoea syndrome. Patients admitted because of adverse drug reactions were excluded. All automatically generated laboratory signals and reports were evaluated by a team consisting of a clinical pharmacologist, a clinician and a pharmacist for their likelihood of being an adverse drug reaction. They were classified by severity and causality. For verified adverse drug reactions, control patients with similar primary diagnosis, age, gender and time of admission but without adverse drug reactions were matched to the cases in order to assess the excess length of hospitalisation caused by an adverse drug reaction. Adverse drug reactions were detected in 12% of patients by the computer-based monitoring system and stimulated spontaneous reporting together (46 adverse reactions in 45 patients) during 1718 treatment days. Computer-based monitoring identified adverse drug reactions in 34 cases, and stimulated spontaneous reporting in 17 cases. Only 5 adverse drug reactions were detected by both methods. The relative sensitivity of computer-based monitoring was 74% (relative specificity 75%), and that of stimulated spontaneous reporting was 37% (relative specificity 98%). All 3 serious adverse drug reactions were detected by computer-based monitoring, but only 2 out of the 3 were detected by stimulated spontaneous reporting. The percentage of automatically generated laboratory signals associated with an adverse drug reaction (positive predictive value) was 13%. The mean excess length of stay was 3.5 days per adverse drug reaction. 48% of adverse reactions were predictable and detected solely by computer-based monitoring. Therefore, the potential for savings on this ward from the introduction of computer-based monitoring can be calculated as EUR56 200/year ($US59 600/year) [ 1999 values]. Computer monitoring is an effective method for improving the detection of adverse drug reactions in inpatients. The excess length of stay and costs caused by adverse drug reactions are substantial and might be considerably reduced by earlier detection.