Potential savings in Medicaid Antiseizure medication reimbursement, 2008–2025: persistent brand-name reimbursement Despite generic availability

BACKGROUND: Despite growing use of generic antiseizure medications (ASMs), brand-name products account for substantial Medicaid reimbursement. We assessed long-term reimbursement trends, potential savings from generic substitution, and patterns following generic entry. RESEARCH DESIGN AND METHODS: Medicaid State Drug Utilization Data (2008-2025) were linked to RxNorm formulations. Utilization was measured in defined daily doses (DDDs), and reimbursement adjusted to 2025Q4 dollars. Hypothetical pre-rebate savings were estimated using formulation-matched generic rates. Event-study, Laspeyres, and state-level analyses assessed post-entry patterns. MAIN OUTCOME MEASURES: ASM utilization, reimbursement, brand-name utilization and reimbursement shares, potential savings from generic substitution, and post-entry variation. RESULTS: Reimbursement for 23 ASMs between 2008-2025 totaled $28.0 billion, including $19.1 billion for brand-name medications. Utilization increased 81.0%, while brand-name utilization share fell from 59.7% to 5.8%. Brand-name ASMs represented 70.8% of reimbursement in 2025. Potential pre-rebate savings totaled $5.8 billion, with 75.2% concentrated in five ASMs. Following generic entry, adjusted brand-name utilization and reimbursement declined 83.7% and 85.8%, respectively, among observations retaining brand-name use. Adjusted state reimbursement shares ranged from 9.6% to 60.2%. CONCLUSIONS: Despite widespread generic adoption, brand-name ASMs continued to account for substantial Medicaid reimbursement. These findings highlight opportunities to evaluate prescribing and reimbursement patterns where generic alternatives exist.