OBJECTIVES: The stability of administered doses of infliximab was examined for Medicare beneficiaries for their first year of treatment following titration. METHODS: Infliximab should be titrated for rheumatoid arthritis (RA) patients to determine their appropriate dose. We hypothesized that with more prescribing experience with infliximab, there may be reductions in the frequency and magnitude of changes in dosage. Using Medicare claims from the 2001 through 2004 5% Standard Analytic Files (SAF), we analyzed cohorts of Medicare beneficiaries with RA who received infliximab. We examined: 1) what proportion kept a constant dosage in the first year after titration, and 2) if this proportion changed over time. We created ten cohorts based on treatment starting date and the presence of six continuous quarters of treatment. Our ten cohorts included 954 beneficiaries, representing an estimated 19,000 beneficiaries. RESULTS: In the year of treatment following titration, 55% of beneficiaries had no increase in dosage and 6% had a decline in dosage. An additional 12% of beneficiaries had only one change in dosage. There was a gradual increase in the percentage of beneficiaries with no increase in dosage between earlier and later cohorts. Between the first and last quarter following titration, across all the cohorts, the average dose increased by 38.5 mg -- equivalent to less than half a vial of infliximab. This change is less than 20% of the average dose. Of the minority of patients who increased dosage (39%), the average increase was just over 1 vial of infliximab (118 mg) -- just over 1/3 of an average dose. CONCLUSION: Over 60% of beneficiaries had no increase in their dose in the year following titration. The average dose over the year adjusts by a relatively modest amount. This dosing stability may facilitate accurate forecasts of resource utilization associated with treatment in the managed care environment.