Objectives: To compare the cost-effectiveness of the treatment of ankylosing spondylitis (AS) with infliximab in the United Kingdom over lifetime estimated from two different clinical trials and adjusted for clinical practice guidelines.

Methods: A cost-effectiveness model was developed to incorporate clinical, epidemiological, and economic data and allow extrapolation of trial results and incorporation of long-term treatment. Assumptions regarding treatment beyond the trials were based on open extensions from the trials and treatment guidelines by the British Society for Rheumatology. Results are presented for both the societal perspective and the perspective of the National Health Service (UK £, discounted 3.5 percent).

Results: Under the assumption that disease activity would be controlled and functional capacity would remain stable while on drug, treatment with infliximab (5 mg/kg every 6 weeks) dominates standard treatment in the societal perspective. In the National Health Service perspective, the cost per quality-adjusted life-year (QALY) gained over lifetime was £28,300 and £26,800 for the two trials. If functional capacity were to deteriorate at half the rate of untreated patients, the cost per QALY gained would be £35,300 and £34,100, respectively. The results are sensitive to the dosing regimen adopted, the discontinuation rate, and assumptions concerning disease progression while on treatment.

Conclusions: The two clinical trials yield the same cost-effectiveness results and the cost per QALY gained with treatment was found to be in the acceptable range.