Etanercept and infliximab for the treatment of psoriatic arthritis: a systematic review and economic evaluation.

OBJECTIVES

To evaluate the clinical effectiveness, safety, tolerability and cost-effectiveness of etanercept and infliximab for the treatment of active and progressive psoriatic arthritis (PsA) in patients who have inadequate response to standard treatment, including disease-modifying antirheumatic drug (DMARD) therapy.

DATA SOURCES

Electronic databases were searched up to July 2004.

REVIEW METHODS

A systematic review evaluated the clinical efficacy and adverse effects of etanercept and infliximab. The efficacy of DMARDs in the treatment of PsA was also reviewed and treatments were compared using Bayesian evidence synthesis methods. Following evaluation of existing economic evaluations of etanercept and infliximab in PsA, a new economic model was developed (the York Model). This utilised the results from the evidence synthesis and data from a range of other sources.

RESULTS

Across the two trials, at 12 weeks, around 65% of patients treated with etanercept achieved an American College of Rheumatology (ACR) 20 {pooled relative risk (RR) 4.19 [95% confidence interval (CI) 2.74 to 6.42]}, demonstrating a basic degree of efficacy in terms of arthritis-related symptoms. In addition, around 45% of patients treated with etanercept achieved an ACR 50 [pooled RR 10.84 (95% CI 4.47 to 26.28)] and around 12% achieved an ACR 70 [pooled RR 16.28 (95% CI 2.20 to 120.54)], demonstrating a good level of efficacy. The subgroup analyses conducted in one trial revealed that the effect of etanercept was not dependent upon patients' concomitant use of methotrexate. In addition, almost 85% of patients treated with etanercept achieved a Psoriatic Arthritis Response Criteria (PsARC) [pooled RR 2.60 (95% CI 1.96 to 3.45). The Psoriatic Area and Severity Index (PASI) results indicate some beneficial effect on psoriasis at 12 weeks; however, the data are sparse. The statistically significant reduction (improvement) in Health Assessment Questionnaire (HAQ) score with etanercept compared with placebo indicates a beneficial effect of etanercept on function. Similar results were seen at 24 weeks, except that the results for PASI 75 and PASI 50 now achieved statistical significance and data for Total Sharp Score annualised rate of progression were available; this was statistically significantly lower in etanercept-treated patients than in placebo-treated patients. Uncontrolled follow-up of patients indicates that treatment benefit may be maintained for at least 50 weeks. At 16 weeks, 65% of patients treated with infliximab achieved an ACR 20 [RR 6.80 (95% CI 2.89 to 16.01)], demonstrating a basic degree of efficacy in terms of arthritis-related symptoms. This level of efficacy was not dependent upon patients' concomitant use of methotrexate. Almost half the patients treated with infliximab achieved an ACR 50 [RR 49.00 (95% CI 3.06 to 785.06)] and over one-quarter achieved an ACR 70 [RR 31.00 (95% CI 1.90 to 504.86)] compared with none of the placebo group, demonstrating a good level of efficacy. In addition, 75% of patients treated with infliximab achieved a PsARC [RR 3.55 (95% CI 2.05 to 6.13)]. The beneficial treatment effect on psoriasis was also statistically significant with a mean difference in percentage change from baseline in PASI of -5 (95% CI -6.8 to -3.3), as was the percentage improvement from baseline in HAQ score with infliximab compared with placebo [mean difference 51.4 (95% CI 48.08 to 54.72)], indicating a beneficial effect of infliximab on functional status. Uncontrolled data from all measures of joint disease, psoriasis and HAQ collected up to 50 weeks of follow-up reflect those at 16 weeks. There were no radiographic assessments, so nothing can be determined about the potential or otherwise of infliximab to delay the progression of joint disease. Using the York cost-effectiveness model, infliximab was consistently dominated by etanercept because of its higher acquisition and administration costs without superior effectiveness. The incremental cost per quality-adjusted life-year (QALY) gained of etanercept compared with palliative care ranged from 14,818 pounds (females, 40-year time horizon) to 49,374 pounds (males, 1-year time horizon) if it is assumed that, when patients eventually fail on biological therapy, their disability (in terms of HAQ score) deteriorates by the same amount as it improved when they initially respond to treatment (rebound equal to gain). Results for etanercept ranged from 25,443 pounds (females, 40-year time horizon) to 49,441 pounds (males, 1-year time horizon) per QALY gained under the assumption that, when patients fail on therapy, their disability level returns to what it would have been had they never responded (rebound equal to natural history).

CONCLUSIONS

The limited data available indicated that etanercept and infliximab are efficacious in the treatment of PsA with beneficial effects on both joint and psoriasis symptoms and on functional status. Short-term data indicated that etanercept can delay joint disease progression, but long-term data are needed. There are no controlled data as yet to indicate that infliximab can delay joint disease progression. Treatment with both etanercept and infliximab for 12 weeks demonstrated a significant degree of efficacy, with no statistically significant difference between them. For both drugs, adverse events were common with mild injection/infusion reactions being the main treatment-related effect. The York model indicated that etanercept is more cost-effective than infliximab as it has a lower cost with little difference in outcomes. The cost-effectiveness of etanercept is also sensitive to assumptions made about the extent of disease progression when patients are responding to therapy. The number of years for which a patient can be safely on biologicals is uncertain so these results should be considered with caution. Further research should include long-term controlled trials to confirm benefits, review adverse events and to explore further the implications of biologic therapy.