OBJECTIVES: This study examined two approaches to estimate drug dosing of infliximab, a commonly used biologic with weight-based dosing, for patients with rheumatoid arthritis (RA). METHODS: A national commercial database was utilized to analyze patients having a medical claim of infliximab therapy initiated between January 2004 and December 2007. Inclusion criteria were patient age ≥18, ≥2 RA diagnosis codes during treatment with infliximab, and 365 days of persistence with infliximab. Patients were excluded if they had other selected inflammatory diseases, had medical/ pharmacy claims of anti-TNFs during 6 months prior to the infliximab index date, or a record of taking abatacept or rituximab while on infliximab. Two methods were compared for estimating dosing of infliximab. Method I, which has been previously published, estimated dosing by dividing the plan’s allowed cost of infliximab by the wholesale acquisition cost (WAC), adjusting for WAC at time of each claim. Method II, a novel approach, used a propensity matching approach to impute patient’s weight onto the commercial database. Since infliximab has weight-based dosing, combining the cost of drug with patient weight allowed for an estimate of dosing. Dosing was expressed as the number of 100 mg vials of infliximab.  Calculated drug dosing using the two methods were compared in terms of means, medians, and correlation coefficients.  RESULTS: There were 20,172 drug dosing events in our sample. Median dose was slightly higher under Method I (3.76 vials) than under Method II (3.39 vials). Mean overall dosing levels were very consistent: 4.01 vials under Method I and 4.11 vials under Method II. Correlations among the two measures were high (rho =0.75).  CONCLUSIONS: Consistent calculations of infliximab drug dosing were obtained using two estimation approaches. Since several commercial databases lack direct information on weight-based drug dosing, such estimation methods may be useful.