Objective: To examine pharmacy costs of a Prior Authorization (PA) restriction on lubiprostone for chronic constipation (CC) patients in a commercial managed care plan. Methods: Cost impact of PA was calculated by estimating annual pharmacy cost differences with PA (medication costs + PA administration) and without PA (medication costs only). Model inputs included CC prevalence estimates from the literature; lubiprostone utilization from IMS Health, 2007; average PA approval rate, PA costs and co-payment from managed care interviews; and lubiprostone wholesale acquisition costs. Annual medication costs in both scenarios included costs and utilization of lubiprostone less co-payment, assuming third-tier placement for lubiprostone. All previously rejected prescriptions were assumed to be accepted after lifting PA, resulting in 11.36% increase in prescription volume. Sensitivity analyses were performed on cost per PA, PA approval rate, and expected increase in prescription volume after lifting PA. Results: CC prevalence was 14.7%, of which 1.14% were lubiprostone users. For a 1-million member plan, this resulted in 1,264 PA requests costing $27 each. Annual cost of PA administration was $34,130. PA acceptance rate was 81.90% (or 1035 approved users). Average number of fills per person per year was 3.8. A 30-day lubiprostone prescription costed $43.40 ($86.40 WAC-$45 co-payment+$2 dispensing fee). Drug costs were $170,737, resulting in total annual cost with PA of $204,867. Total costs without PA were $190,125, based on additional 118 approved users, resulting in annual savings of $14,742. Sensitivity analyses indicated break even scenarios from removing a PA on lubiprostone when cost per PA >$15.34 or PA approval rate >74.83%, or expected increase in prescriptions from lifting PA <19.99%. Conclusion: PA program for lubiprostone offers no financial savings to a health plan based on current approval rates and annual utilization for patients suffering from CC in the base case as well as in sensitivity analyses.