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Objective: To describe dosing patterns for tumor necrosis factor (TNF) antagonists in patients with rheumatoid arthritis from health care provider and payer point of interest.Research design and methods: Using privately insured US claims data from 31 large employers covering 31 companies across the US, rheumatoid arthritis (RA) patients were identified and three cohorts were defined based on first TNF-antagonist treatment (adalimumab, etanercept, or infliximab) administered after January 1, 2003. Dosageadjustment patterns were assessed during the following 12-month period. Changes in dosage (both increases and decreases) and maintenance of a stable dosage were evaluated. For the health care provider point of interest, a new algorithm was developed to assess treatment patterns with chronic injectable therapies that incorporated the potential inconsistency between days of supply and prescription-gap data, thus providing the actual use of TNFantagonist treatment. For the payer, usage data addressed whether the TNF antagonist was used at a greater dosage than recommended. Differences in baseline characteristics and dosage change rates between cohorts were tested using Chi-Square tests for categorical variables and Wilcoxon tests for continuous variables.Results: From the health care provider point of interest, 83.4% of adalimumab-treated patients (n = 205) initially received the recommended dosage, 10.2% received less, and 6.3% received more; 87.7% of etanercept-treated patients (n = 455) initially received the recommended dosage, 11.2% received less, and 1.1% received more; and 83.8% of infliximab-treated patients (n = 148) started with 2–4 vials (the recommended dosage is based on the weight of the patient, not total milligrams). All treatments had similar dosage decrease and discontinuation rates. Maintenance of stable dosage was lower for infliximab (20.9%) than adalimumab (37.1%) and etanercept (39.1%); both p < 0.01. The infliximab dosage-increase rate (35.1%) was greater than adalimumab (3.9%) and etanercept (0); both p < 0.01. From the payer point of interest, dosage-increase rate was greater for infliximab (28.3%) than adalimumab (8.7%) and etanercept (6.9%), both p < 0.01.Conclusions: Infliximab had greater dosage-increase rates than adalimumab and etanercept. Adalimumab and etanercept had similar dosage-increase rates. All treatments had similar dosage-decrease and discontinuation rates. Maintenance of stable dosage was lower for infliximab than for adalimumab and etanercept. The study has the usual limitation of claims data analysis in that clinical details might be insufficient to draw causal inference. [ABSTRACT FROM AUTHOR]