Valuing treatment with infliximab for ankylosing spondylitis using a willingness-to-pay approach

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

METHODS: Data were used 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). WTP was included at baseline of 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 regressions (ZINB).

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

CONCLUSION: In a hypothetical scenario, three quarter of patients with AS on long-term infliximab stated to be willing to pay an out-of-pocket contribution for this treatment. Treatment response contributed to the willingness as well as to the amount patients are willing to pay. This article is protected by copyright. All rights reserved.