Real-world anti-tumor necrosis factor treatment in rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis: cost-effectiveness based on number needed to treat to improve health assessment questionnaire.

OBJECTIVE: To determine the effectiveness and cost-effectiveness of anti-tumor necrosis factor (anti-TNF) medications in a real-world environment for the treatment of rheumatoid arthritis (RA), psoriatic arthritis (PsA), and ankylosing spondylitis (AS) using the Health Assessment Questionnaire (HAQ).

METHODS: We created a database of patients with RA, PsA, or AS treated with anti-TNF agents (etanercept, infliximab, or adalimumab) at a large outpatient rheumatology clinic. Patient characteristics, baseline HAQ prior to treatment, subsequent yearly HAQ, and reasons for termination were collected. The cost based on percentage of patients achieving >or= 0.2 improvement in HAQ (minimal clinically important difference, MCID) was calculated using the 2008 direct cost (Cdn) of the medication.

RESULTS: Data were available on 297 patients (206 with RA, 57 PsA, 34 AS). The mean age was 55 years, with 12 years of disease, and the mean baseline HAQ (standard error, SE) was 1.37 (0.04). The changes in HAQ (SE) at Years 1, 2, and 3 were -0.31 (0.04), -0.24 (0.06), and -0.27 (0.07) for annual cost to achieve MCID of $41,636, $42,077, and $42,147, respectively. The number needed to treat (NNT) was 1.94 (RA), 1.88 (PsA), and 2.30 (AS). There were no statistical differences between the diseases studied.

CONCLUSION: We obtained data on the effectiveness and cost-effectiveness of anti-TNF drugs using the HAQ score, which is known to be an excellent predictor of work disability, morbidity, and mortality. HAQ scores decreased with treatment and were sustained throughout the 3-5 years of followup. The NNT of approximately 2 seems favorable and was similar between diseases.