OBJECTIVES: This study describes the economic impact and prescription utilization patterns of instituting a proton pump inhibitor (PPI) conversion program, in which the preferred PPI was changed from Prevacid (lansoprazole) to Aciphex (rabeprazole). METHODS: A retrospective claims-based analysis was conducted in a managed care plan with approximately 175,000 members from March 2000 through December 2000. Two four-month periods, corresponding to pre- and post-conversion periods (separated by the actual two-month conversion period) were defined for comparison of PPI pharmacy costs and utilization patterns. Wholesale acquisition cost (WAC) was used for pharmacy costs. A paired t-test analysis was used to assess statistical significance in the change in PPI pharmacy costs and daily number of tablets consumed (DACON) in a subset of patients with an equal number of PPI prescriptions in the pre and post conversion periods. RESULTS: There were a total of 24,980 PPI prescriptions in 6453 patients in the 10- month study period. Demographics for the 6453-patient data set were: 59% female, 41% male, 82% between 26 and 75 years old. Of these 6453 patients, 932 had an equal number of prescriptions in the pre and post conversion periods. In this subset, average PPI prescription costs decreased by $8.02 +/- 36.14 (p<0.0001) and DACON decreased by 0.02 +/- 0.22 (p<0.01). Overall in the 6453 patients, market share for Prevacid decreased from 90% to 9%, while Aciphex market share increased from 7% to 90%. For the total 10-month study period for the 6453 patients, PPI DACON averaged: Aciphex 1.06, Prevacid 1.08, Prilosec 1.13, Protonix 1.03. CONCLUSION: For both the 932-patient subset and the overall 6453-patient data base, converting prescriptions from Prevacid to Aciphex resulted in a significant reduction in PPI pharmacy costs and PPI DACON in the Scott & White Health Plan.