Eluxadoline Utilization in Medicare Part D, 2016–23: National Trends, Geographic Variation, Prescriber-Type Patterns, and Spending

BACKGROUND: Eluxadoline is a US Food and Drug Administration-approved therapy for irritable bowel syndrome with diarrhea and has important contraindications that may influence uptake in older adults. Medicare Part D dispensing patterns remain poorly characterized. OBJECTIVE: This study aimed to characterize national and state-level trends in eluxadoline dispensing and spending in Medicare Part D from 2016-2023, including geographic variation in population-adjusted rates and differences in dispensing intensity by prescriber type. METHODS: We conducted a retrospective repeated cross-sectional analysis using Centers for Medicare & Medicaid Services Medicare Part D Prescribers-by Provider and Drug Public Use Files from 2016 to 2023. Utilization was summarized using standardized 30-day fills (primary) and claims (secondary); state intensity was measured as fills per 100,000 Part D utilizers. Geographic concentration and outliers in state rates were assessed using Gini coefficients and median absolute deviation-based outlier detection. Prescriber-type differences in dispensing intensity were evaluated with negative binomial models of claims with National Provider Identifier-clustered standard errors. RESULTS: The Public Use Files contained 7826 prescriber-year observations from 3866 prescribers. National 30-day fills rose from 4410.9 (2016) to 19,860.2 (2018) and declined to 15,326.0 (2023). Median state rates increased from 7.3 per 100,000 (2016) to 43.7 (2018) and were 27.6-35.9 in 2019-23; California, Texas, New Jersey, New York, and Florida accounted for 39.5% of fills. State utilizer counts correlated with total fills (ρ 0.80-0.89) more than adjusted rates (ρ 0.03-0.34). Geographic concentration remained moderate in 2018-23 (Gini 0.307-0.352), and New Jersey was a recurrent high-rate outlier. Gastroenterologists comprised 41.5-57.4% of prescribers and had higher claim intensity than primary care (incidence rate ratio 1.17, 95% confidence interval 1.13-1.21). Inflation-adjusted cost per standardized fill increased from $1021 to $1414. CONCLUSIONS: Eluxadoline dispensing in Medicare Part D is geographically concentrated and heterogeneous, with higher intensity among gastroenterologists. These descriptive benchmarks may inform medication-use monitoring, access and coverage evaluation, and future beneficiary-level studies of safety and appropriateness in irritable bowel syndrome with diarrhea care.