OBJECTIVES: On July 12, 2005 the Arkansas Medicaid program implemented a prior approval policy for calcium channel blockers (CCBs) in which Diltiazem ER, Dynacirc CR, Nifedipine ER, XL, CC, CR, Norvasc, and Verapamil SR, SA, were the preferred drugs. The objective of this study was to estimate the impact of this policy on CCB expenditures. METHODS: This study utilized a time series panel design to evaluate the impact of the policy using Arkansas Medicaid administrative claims data obtained from January 2003 through May 2006. Auto-Regressive Integrated Moving Average (ARIMA) time series models were specified using monthly prescription expenditures and utilization in the pre-policy period (January 2003 – June 2005) to forecast expenditures and utilization in the post-policy period. The Medicaid payer perspective was used and all prescription costs were calculated based on the amount paid for each claim adjusted for product specific CMS rebates. RESULTS: The average forecast expenditures for CCBs for August 2005 – May 2006 was $426,706 (95%CI: 410,356-443,055) per month and observed expenditures were $331,547 indicating that the policy change was associated with a 22% reduction in CCB expenditures or $95,159 (95%CI: 78,809- 111,508) per month. The average monthly savings were $114,521 prior to January 2006 and were $75,796 after Medicare dual eligibles began receiving Part-D benefits. Non-significant reductions in CCB utilization were observed in the initial 4 months following the policy, however by May 2006, 4,065 (95%CI: 3,811-4,319) recipients were expected to be taking CCBs but only 3,046 actually had a CCB prescription filled. CONCLUSION: This CCB preferred drug list resulted in substantial savings of approximately $100,000 per month. Some of the savings appear to be a result of reduced utilization of CCBs which may indicate that other cardiovascular drugs may have been used in place of CCBs or CCB discontinuation.