PROBLEM: Drugs are often given intravenously even when the patient is able to swallow and when an oral form would be more cost-effective. DESIGN: Evaluation of the impact of a multifaceted intervention on the early switch from intravenous to oral administration of proton pump inhibitors (PPI) in a hospital setting. The interrupted time series of intravenous PPI consumption was analysed. BACKGROUND AND SETTING: At a French University Hospital, the Drug Committee, composed of multidisciplinary pharmacy and medical staff, addressed the issue of increasing consumption of intravenous PPI drugs (May 2003). Strategy for change: Letters to department heads, academic analyses from members of the Drug Committee, paper reminders at the point of care and audit-feedbacks by pharmacists. Monitoring of consumption and repeated reminder letters were planned. EFFECT OF CHANGE: The consumption of PPI was stable before the first intervention (mean level: 954 units/month). An immediate decrease occurred after the first Drug Committee letter (30% relative reduction, 95% CI -16% to -46%; p<0.001) with a significant trend change during the first multifaceted intervention (-24 units/month, 95% CI -42 to -7; p = 0.007). After the end of the outreach visits (July 2004), the consumptions increased (+32 units/month, 95% CI: 14 to 50, p<0.001). The second intervention had no significant impact. LESSONS LEARNT: A complex intervention (audit, feedbacks, outreach visits) had an effect on practice. It was not sustained even after a less resource-intensive intervention. Other types of interventions are needed that could be continuously implemented to improve ordering practices long term.