Medicine (Baltimore). 2024 Sep 13;103(37):e39476.doi: 10.1097/MD.0000000000039476.

Shardool Patel ¹, Jessica Walsh ¹, Derek Pinnell ¹, Shaobo Pei ¹, Wei Chen ¹, Jorge Rojas ^2 3, Anitha Rathod ¹, Jessica Johnson ¹, Andrew Gawron ¹, Jeffrey R Curtis ⁴, Joshua F Baker ⁵, Grant W Cannon ¹, David Wu ⁶, Miao Lai ¹, Brian C Sauer ¹

Author information

¹Salt Lake City Veterans Affairs Medical Center and Department of Internal Medicine, University of Utah, Salt Lake City, UT.

²Puget Sound Veterans Affairs Medical Center, Seattle, WA.

³Department of Internal Medicine, University of Utah, Salt Lake City, UT.

⁴Division of Clinical Immunology and Rheumatology, University of Alabama at Birmingham, Birmingham, AL.

⁵Corporal Michael J. Crescenz VA Medical Center and School of Medicine, University of Pennsylvania, Philadelphia, PA.

⁶Merck and Company, Inc, Rahway, NJ.

Abstract

The Veterans Health Administration (VHA) listed the infliximab (IFX) biosimilar, IFX-dyyb (Inflectra), on the Veterans Affairs National Formulary (VANF) in May 2017. In September 2018, biosimilar IFX-abda (Renflexis) became the VANF IFX product. The recommended formulary changes from one IFX biosimilar to another provided a unique opportunity to study IFX utilization patterns in IFX-naïve Veterans with Inflammatory Bowel Disease (IBD). This study aimed to describe IFX and healthcare utilization during the 365 days after initiation with IFX reference product (RP) or biosimilars IFX-dyyb and IFX-adba. This descriptive study was performed using the VHA Corporate Data Warehouse. All Veterans initiated on IFX-RP (Remicade) or biosimilars IFX-dyyb and IFX-adba between September 1, 2016 and December 30, 2019 were included and followed for 365 days. Veterans enrolled in the VHA for at least 365 days with no evidence of IFX before their index date were considered IFX-naïve. Continuous data on IFX use, laboratory measurements, and healthcare utilization were reported with means, 95% confidence interval (CI), medians, and interquartile ranges. Frequency, proportions, and 95% CIs were presented for categorical variables. Statistical tests included ANOVA and Kruskal-Wallis for continuous outcomes, Poisson regression for count-based outcomes (i.e., healthcare utilization visits), and Chi-square for dichotomous outcomes. The study identified 1763 IFX-naïve patients with IBD, and 785, 441, and 537 was indexed to RP, IFX-dyyb, and IFX-adba, respectively. Statistical differences were observed in IFX utilization measures related to dosing, adherence, and persistence. The proportion of days covered (PDC) during the 365-day follow-up period varied among the IFX groups: IFX-RP at 66%, IFX-dyyb at 60%, and IFX-abda at 69% (P value < .001). Persistence with the index IFX product during the 365-day follow-up period also varied: IFX-RP at 43%, IFX-dyyb at 32%, and IFX-abda at 51% (P value < .001). Healthcare utilization and laboratory findings were similar among the IFX groups. IFX utilization and laboratory patterns were clinically similar among the IFX biosimilars and RP groups, suggesting that providers did not modify their practice with biosimilars. Statistically significant differences in IFX utilization patterns are explained by formulary dynamics when the VANF product switched from IFX-dyyb to IFX-abda.