ObjectivesEarly switch from intravenous to oral therapy of bioequivalent drugs has major advantages but remains challenging. At our hospital, a basic clinical rule was designed to automatically alert the physician to review potential intravenous to oral switch (IVOS). A rather low acceptance rate was observed. In this study, we aimed to develop, validate and investigate the effect of more advanced clinical rules for IVOS, as part of a centralised pharmacist-led medication review service.Design and settingA quasi-experimental study was performed in a large teaching hospital in Belgium using an interrupted time series design.InterventionA definite set of 13 criteria for IVOS, focusing on the ability of oral absorption and type of infection, was obtained by literature search and validated by a multidisciplinary expert panel. Based on these criteria, we developed a clinical rule for paracetamol and one for ten bioequivalent antibiotics to identify patients with potentially inappropriate intravenous prescriptions (PIVs). Postintervention, the clinical rule alerts were reviewed by pharmacists, who provided recommendations to switch in case of eligibility.Primary and secondary outcome measuresA regression model was used to assess the impact of the intervention on the number of persistent PIVs between the preintervention and the postintervention period. The total number of recommendations, acceptance rate and financial impact were recorded for the 8-month postintervention period.ResultsAt baseline, a median number of 11 (range: 7–16) persistent PIVs per day was observed. After the intervention, the number reduced to 3 (range: 1–7) per day. The advanced IVOS clinical rules showed an immediate relative reduction of 79% (incidence rate ratio=0.21, 95% CI 0.13 to 0.32; p<0.01) in the proportion of persistent PIVs. No significant underlying time trends were observed during the study. Postintervention, 1091 recommendations were provided, of which 74.1% were accepted, resulting in a total 1-day cost saving of €4648.35.ConclusionsWe showed the efficacy of advanced clinical rules combined with a pharmacist-led medication review for IVOS of bioequivalent drugs.