Objective Our objective was to evaluate the prevalence of discrepancies between primary care electronic medication records (EMR) and patient reported medication (PRM) in ambulatory patients starting a hospital dispensing treatment (HDT) at a hospital-based ambulatory care pharmacy (HACPh). Our secondary aims were to analyse factors associated with the presence of discrepancies and their impact on the prevalence of potential drug–drug interactions (DDIs) with the HDT.

Methods Retrospective study including 230 patients starting a HDT at the HACPh. Pharmacists interviewed patients and PRM was compared with EMR. Discrepancies were classified as omissions (medication in the PRM not present in the EMR) and commissions (medication active in the EMR that the patients were not taking). Potential DDIs with the HDT were screened, and univariate and multivariate analyses were performed to detect factors associated with the presence of discrepancies.

Results We identified 221 discrepancies in 116 (50.4%) patients. Being visited by three or more medical specialties (OR 1.93, 95% CI 1.11 to 3.37) and attending private healthcare (OR 4.36, 95% CI 1.14 to 16.72) in the 12 months before the study inclusion were the factors independently associated with the presence of discrepancies. Among patients with commissions (n=91), 15.4% had a potential DDI between the HDT and one medication from the EMR that they were not taking at that moment. Among patients with omissions (n=45), 11.1% had a potential DDI between the HDT and a medication in the PRM not present in the EMR.

Conclusions About 40% of patients had one or more medications in the EMR which they were not taking and one fifth used medications that were not listed in the EMR. EMR should not be used as the only source of information when screening for DDIs, especially in patients followed by different medical specialties or combining private and public healthcare.