The burden of ankylosing spondylitis and the cost-effectiveness of treatment with infliximab (Remicade®)

Objectives. In the past, treatment options for ankylosing spondylitis (AS) have been limited, and the introduction of new treatments such as infliximab will have a noticeable impact on health-care budgets. The objective of this study was therefore to assess the current burden of the disease and estimate the cost-effectiveness of infliximab treatments. Methods. A cross-sectional retrospective observational study of resource consumption and utility related to disease severity was performed in patients who had participated in a population survey between 1992 and 1994 at the University of Bath and patients regularly followed at the Royal National Hospital for Rheumatic Diseases in Bath for up to 9 years. Mean costs and utility were estimated using a regression model including age, gender, disease duration, disease activity and functional status, and disease development was expressed as annual progression of functional disability. Cost-effectiveness of infliximab was modelled using a 3-month placebo-controlled clinical trial with open 1-yr extension in 70 patients, over a total time frame of 2 yr. In the model, costs and utility controlled for disease severity and age from the observational study were assigned to individual patients. The effect of long-term treatment was evaluated in a hypothetical model over 30 yr. Results. Fifty-seven per cent of patients answered the questionnaires. The mean age was 57 (S.D. 11.2) yr, 74% were male and mean disease duration was 30.2 (11.7) yr. Mean total costs were estimated at £6765 (S.D. £166). Indirect costs represented 57.9% and non-medical costs such as investments and informal care accounted for 16.5% of total costs. Mean utility was 0.67 (0.21). In the main model, mean costs for untreated patients are estimated at £25,128. For the infliximab group, mean costs (excluding treatment) are estimated at £17,240, a reduction of 31%. Thus, part of the treatment cost was offset by savings in other resources (£7888), leaving an incremental cost of £6214. Treatment increased the number of quality-adjusted live years (QALYs) by 0.175 QALYs, leading to a cost per QALY gained of £35,400 for the first year of treatment. When treatment is assumed to continue for the full 2 yr, the cost per QALY is £32,800. When infliximab infusions are given every 8 weeks instead of every 6 weeks, the cost per QALY is reduced to £17,300. In the long-term model, the cost per QALY is estimated at £9600. Conclusions. Non-medical costs and production losses dominate costs in AS, and economic evaluation must therefore adopt a societal perspective. The cost of treatment with infliximab is partly offset by reductions in the cost of the disease and patients’ quality of life is increased, leading to a cost per QALY gained in the vicinity of £30,000 to £40,000 in the short term, but potentially below £10,000 in the long term.