Impact of a Restrictive Formulary on glycemic control compared with an Open Formulary

Abstract Introduction In 2019, California Governor Gavin Newsom introduced executive order N‐01‐19, which transitioned California's Medicaid (Medi‐Cal) health plan pharmacy benefits from multiple managed care plans to a single‐payer system. This transition occurred on January 1, 2022, and Medi‐Cal stopped enforcing formulary restrictions for beneficiaries. Objectives This study compared glycemic control of hemoglobin A1c in a pharmacist‐led diabetes clinic during an open versus restrictive formulary. Methods This is a retrospective cohort study of Medi‐Cal patients seen in a pharmacist‐led diabetes clinic at Kern Medical in Bakersfield, California between January 2021 and September 2022. All new patients with type 2 diabetes and an A1c greater than 6.9% seen at the clinic between January and September 2021 were classified as the Restrictive Formulary group and those seen between January and September 2022 were the Open Formulary group. The primary end point was mean change in A1c at first follow‐up. Secondary end points included attainment of an A1c <7%, change in weight, blood pressure, cholesterol, and statin use, and change in estimated monthly drug expenditure for glucose‐lowering medications per patient. Safety end points included diabetes‐related visits to Kern Medical's emergency room and hospitalizations. Results While both the Restrictive and Open Formulary groups had significant reductions in mean A1c from a baseline of −0.74 ± 2.1 ( p = 0.02) and − 2.7 ± 2.4 ( p < 0.001), respectively, the magnitude of A1c reduction was greater in the Open group ( p < 0.001). For secondary outcomes, the Open group saw a higher utilization of agents with known cardiovascular and renal benefits. The Open group had a modest weight reduction (−2.5 kg ± 4.4 kg, p = 0.027). There was no significant difference in the cost of diabetes therapy between the two groups ( p = 0.12). Conclusions An open formulary resulted in better glycemic control without significantly increasing the average monthly cost of diabetes medications.