Categorization of infliximab dose changes and healthcare utilization and expenditures for patients with rheumatoid arthritis in commercially insured and Medicare-eligible populations

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Abstract
Objective: To evaluate how changes in infliximab dose influence resource utilization and expenditures for patients with rheumatoid arthritis (RA). Research design and methods: A retrospective analysis using claims from January 1, 1999 through March 31, 2005 in the MedStat MarketScan databases for RA patients who had an increase, decrease, or no change in infliximab dose within 1 year of initiating therapy. Eligibility criteria included at least one claim with a diagnosis of RA and no biologic treatment within 6 months before the index infliximab claim, continuous health plan enrollment (commercial or Medicare) for 6 months before and 12 months after the index date, and three consecutive infliximab infusions. The index and final infliximab doses were estimated from claims data. Results: Data were included for 1678 commercially insured patients and 616 Medicare-eligible patients; 45.4% and 39.3%, respectively, had an increase in dose, 24.7% and 43.2%, respectively, had a decrease in dose, and 29.9% and 17.5%, respectively, had no change in dose. Overall, resource utilization was higher in the increase-in-dose groups and lower in the no change-in-dose groups when compared with the decrease-in-dose groups for both cohorts. Medical costs were also highest for the increase-in-dose groups for both cohorts. Pharmacy expenditures for the no-change-in-dose groups were lower than the decrease-in-dose groups in both cohorts. Conclusions: An increase in dose was the most common dose change for the commercial cohort, while a decrease in dose was the most common dose change for the Medicare-eligible cohort. Patients with an increase in dose had the highest utilization and expenditures while those with no change in dose had the lowest levels. The nature of this utilization needs to be examined to better understand how dosing changes may influence medical utilization. Changes in dose were defined by the difference between the first and final doses and may not have captured changes in interim doses.