Y Richard Wang1, Mark V Pauly. 1. Public Policy Department, AstraZeneca Pharmaceuticals, Wilmington, Del 19850-5437, USA. y.richard.wang@astrazeneca.com
Abstract
BACKGROUND: A restrictive drug formulary may influence how physicians treat other, unaffiliated patients, a phenomenon known as the "spillover effect." In a previous study we found significant spillover effects from Maine's Medicaid formulary. OBJECTIVE: To determine whether similar spillover effects exist for private insurers with less restrictive formularies and less dominant market presence. STUDY DESIGN: We treated PacifiCare's formulary changes for proton pump inhibitors (PPIs) as a natural experiment and studied whether these changes spilled onto non-PacifiCare patients in California. Rabeprazole and pantoprazole are the newly preferred PPI products. METHODS: We analyzed the physician-level before-and-after changes in prescribing of rabeprazole and pantoprazole for PacifiCare and non-PacifiCare patients. We also estimated the effect of PacifiCare share of practice on spillover effects using linear regressions. RESULTS: The number of rabeprazole and pantoprazole prescriptions increased simultaneously for non-PacifiCare patients and the increase was positively associated with PacifiCare share of practice. For non-PacifiCare prescriptions, a 10% increase in PacifiCare share of practice led to a 3.3% share increase for rabeprazole and a 1.6% share increase for pantoprazole, respectively (both P < .001). CONCLUSIONS: PacifiCare's PPI formulary changes generated significant spillover effects onto non-PacifiCare patients in California.
BACKGROUND: A restrictive drug formulary may influence how physicians treat other, unaffiliated patients, a phenomenon known as the "spillover effect." In a previous study we found significant spillover effects from Maine's Medicaid formulary. OBJECTIVE: To determine whether similar spillover effects exist for private insurers with less restrictive formularies and less dominant market presence. STUDY DESIGN: We treated PacifiCare's formulary changes for proton pump inhibitors (PPIs) as a natural experiment and studied whether these changes spilled onto non-PacifiCare patients in California. Rabeprazole and pantoprazole are the newly preferred PPI products. METHODS: We analyzed the physician-level before-and-after changes in prescribing of rabeprazole and pantoprazole for PacifiCare and non-PacifiCare patients. We also estimated the effect of PacifiCare share of practice on spillover effects using linear regressions. RESULTS: The number of rabeprazole and pantoprazole prescriptions increased simultaneously for non-PacifiCare patients and the increase was positively associated with PacifiCare share of practice. For non-PacifiCare prescriptions, a 10% increase in PacifiCare share of practice led to a 3.3% share increase for rabeprazole and a 1.6% share increase for pantoprazole, respectively (both P < .001). CONCLUSIONS: PacifiCare's PPI formulary changes generated significant spillover effects onto non-PacifiCare patients in California.