Inconsistencies in the days supply values reported in pharmacy claims databases for biologics with long maintenance intervals

BACKGROUND: Days supply values reported in large administrative claims databases are commonly used to estimate drug exposure and quantify adherence and persistence with prescribed therapy. In recent claims database studies assessing treatment patterns for biologic therapies, a high frequency of 28-31–days supply values has been observed for therapies with label-recommended maintenance dosing intervals longer than 4 weeks. Such inconsistencies suggest potential inaccuracy of days supply data. OBJECTIVES: To confirm the existence and describe the extent of inconsistencies in the reported days supply values and the documented fill intervals among prescription claims from administrative claims databases for 2 different biologics with label-recommended maintenance dosing intervals longer than 4 weeks and 2 biologics with intervals less than or equal to 4 weeks. METHODS: Using data from 2 large US administrative claims databases (IBM MarketScan Commercial Claims and Encounters and the Optum Clinformatics Data Mart Socio-economic Status [SES]), the reported days supply values and associated intervals between consecutive fills for 2 biologics with maintenance dosing intervals longer than 4 weeks (guselkumab and ustekinumab) and 2 with intervals less than or equal to 4 weeks (adalimumab and ixekizumab) were described. For all fill pairs with reported days supply values of 28-31 days, the percentage with inconsistent fill intervals (defined as >45 days or >60 days) was calculated. RESULTS: Across all datasets, the proportions of fill pairs with inconsistent days supply values and fill intervals (ie, days supply values of 28-31 days but fill intervals of >45 days) were 41.8%-73.4% for guselkumab, 33.4%-59.4% for ustekinumab, 8.5%-9.5% for adalimumab, and 7.3%-11.4% for ixekizumab. The same trend was observed across these biologics when using more than 60 days to define an inconsistent fill interval. Unlike adalimumab and ixekizumab, a wide distribution of fill intervals was observed among guselkumab and ustekinumab fill pairs with 28-31 days supply values, with peaks evident at approximately 28-31 days as well as around the label-recommended maintenance dosing intervals for these therapies (56 or 84 days). CONCLUSIONS: This study demonstrated a large discrepancy between days supply values and fill intervals reported in administrative claims data for biologics with label-recommended maintenance dosing intervals longer than 4 weeks (ie, guselkumab and ustekinumab), potentially suggesting widespread underestimation of days supply values for these therapies. Such inconsistencies in the reported days supply values may lead to underestimation of treatment adherence and persistence for these biologics, which could be mitigated by systematic data imputation.