Valuing Treatment With Infliximab for Ankylosing Spondylitis Using a Willingness-to-Pay Approach

To investigate willingness to pay (WTP) for treatment with infliximab by patients with ankylosing spondylitis (AS) and explore factors associated with WTP.

Data from 85 patients participating in the European AS Infliximab Cohort (EASIC) open-label extension of the AS Study for the Evaluation of Recombinant Infliximab Therapy (ASSERT) were used. WTP was included at baseline in EASIC and comprised a hypothetical scenario exploring whether the patient would be willing to pay for beneficial effects of infliximab and, if so, what amount they would be willing to pay per administration. Factors associated with WTP were explored using zero-inflated negative binomial (ZINB) regressions.

Of the 85 patients, 63 (74.1%) were willing to pay, and among these, the mean amount they were willing to pay per administration was €275 (median €100 [interquartile range €50-200]). Multivariable ZINB analysis showed that Assessment of SpondyloArthritis international Society criteria for 20% improvement (ASAS20) response was associated with a 7-fold lower likelihood to pay 0 euros (odds ratio [OR] 0.14 [95% confidence interval (95% CI) 0.03-0.71]) and a 3-fold increase in the amount willing to pay (exp(β) = 3.32 [95% CI 1.44-7.69]). In addition, the country of residence was associated with a lower likelihood to pay 0 euros (OR 0.07 [95% CI 0.02-0.36]), while increased age was associated with the amount willing to pay (exp(β) = 1.05 [95% CI 1.01-1.09]).

In a hypothetical scenario, three-quarters of patients with AS receiving long-term infliximab stated that they were willing to pay an out-of-pocket contribution for this treatment. Treatment response contributed to the willingness as well as to the amount patients were willing to pay.