External validation of the Medication Risk Score in polypharmacy patients in general practice: A tool for prioritizing patients at greatest risk of potential drug-related problems.

Drug-related problems are important causes of patient harm and increased healthcare costs. To assist general practitioners in prioritizing patients in need of a critical medication review, we aimed to assess the ability of the Medication Risk Score (MERIS) to stratify patients with polypharmacy in general practice according to their risk of drug-related problems. We conducted a cross-sectional multi-centre external validation study. Patients receiving more than five concomitant medications (polypharmacy) were eligible. The outcome was potentially serious drug-related problems as evaluated by expert consensus. Performance was assessed in terms of calibration and discrimination indices. Of 497 patients, 489 were included in the main analysis. The median age (interquartile range) was 70.5 years (60-79). In total, 372 potentially serious drug-related problems were observed in 253 patients (52%). The MERIS was well calibrated above a score level of 10. The area under the receiver operating characteristic curve was 0.70 (95% confidence interval: 0.65-0.74). The performance of the MERIS was fair in patients with polypharmacy in general practice. Given the scale of drug-related problems and the lack of efficient prioritization tools in this setting, the MERIS could be a useful risk indicator to complement usual practice.