OBJECTIVES: In 2001, the Veterans Affairs Healthcare System implemented a proton pump inhibitor (PPI) conversion to rabeprazole in patients who were previously on either omeprazole or lansoprazole. An unpublished study by Humphries and colleagues showed that rabeprazole, when taken concomitantly with digoxin, increased the digoxin trough level by 22%, AUC by 19%, and Cmax by 29%. Safety during the conversion of patients already taking digoxin and a PPI chronically was uncertain. Therefore, a medical center observational, nonrandomized prospective drug utilization evaluation (DUE) was designed to ensure safety throughout the conversion process. METHODS: One hundred and twelve patients were identified via prescription data base search. Pre- and post-digoxin levels were drawn to assess for the potential drug interaction and toxicity associated with the switch from lansoprazole or omeprazole to rabeprazole. Levels were scheduled for baseline and 7-10 days following conversion to rabeprazole. All patients were converted to rabeprazole upon clinic visit through pharmacist intervention. Adverse effects were monitored at conversion and during follow-up visit. RESULTS: Forty-seven patients completed the DUE conversion project. Mean pre-and post-digoxin levels were 0.85 ± 0.93 ng/ml and 0.86 ± 0.51 ng/ml, respectively (p=0.93). Twelve patients had digoxin levels elevated more than 15%, 3 of whom were symptomatic. CONCLUSIONS: A statistically significant drug interaction was not observed. However, due to absence of a control group in this DUE, we recommend baseline digoxin levels and patient education of potential signs and symptoms of digoxin toxicity to ensure safety during a medication conversion. It does not appear that post-conversion digoxin levels are warranted unless accompanied by signs and symptoms of toxicity.