To describe the effect of indirect costs for patients with early rheumatoid arthritis (RA) within the COBRA trial (Combinatietherapie Bij Reumatoide Artritis) on the cost-effectiveness of both therapies. Analyses of the efficacy and direct costs of the treatments have already been reported.
Patients with early RA selected for the 56-week trial were randomly assigned to prednisolone, methotrexate, and sulfasalazine (the COBRA combination) (n = 76, tapered after 28 weeks) or to sulfasalazine (SSZ; n = 79, of which 78 patients were evaluable) alone. The main efficacy outcomes were a pooled index and radiographic damage score in hands and feet, and utilities. Direct and indirect costs were measured (from a societal perspective) by means of cost diaries and interviews completed by patients during the intervention phase and the followup phase, each lasting 28 weeks. Differences in mean costs between groups and cost-utility ratios were evaluated by applying nonparametric bootstrapping techniques.
In the first 28 weeks, indirect costs per patient totaled US $2,578 and US $3,638 for COBRA and SSZ therapy, respectively (p = 0.09). The total costs were $5,931 and $7,853, respectively (p < 0.05). These differences were lost in the second 28 weeks. For the total period the mean total costs per patient were $10,262 and $12,788, respectively (p = 0.11). Sensitivity analyses showed robustness of the data. The point estimate of the cost per quality-adjusted life-year based on the rating scale was negative at $-385, suggesting dominance of COBRA (more effect at lower cost).
COBRA therapy adds additional disease control (improvements in disease activity, physical function, and rate of damage progression) at lower or equal cost compared to SSZ in early RA.