As described above, the CDR base case varied the model time horizon and health-state utility values (using two scenarios), as well as assessing the impact of excluding the effect of real-world evidence on the transition probabilities after one year in the maintenance phase of the model. CDR also corrected the error that overestimated the ICUR results for the mixed dosage. One-way and multi-way reanalyses were performed varying these model components (Appendix 3). The model was particularly sensitive to variations in health-state utility values and to the exclusion of real-world evidence when estimating transition probabilities.

The CDR base case for ustekinumab when compared with conventional therapy in the population experiencing an FCTO resulted in an ICUR of $115,474 per QALY gained and, in the population experiencing a failure of anti-TNF therapy, $131,297 per QALY gained. For the mixed population, ustekinumab resulted in an ICUR of $119,058 per QALY when compared with conventional therapy.

Among the available biologic therapies in patients who had experienced an FCTO, ustekinumab every 12 weeks was the most cost-effective, with an ICUR of $115,474 per QALY compared with conventional therapy, followed by ustekinumab mixed dosage (every eight weeks/every 12 weeks), with an ICUR of $623,571 per QALY when compared with ustekinumab every 12 weeks, then finally by ustekinumab every eight weeks with an ICUR of $658,533 per QALY compared with ustekinumab mixed dosage. Other biologics were either dominated or subjected to extended dominance. In the patients with a failure of anti-TNF therapy, the most cost-effective treatment was biosimilar infliximab, with an ICUR of $90,277 per QALY compared with conventional therapy, followed by ustekinumab every 12 weeks with an ICUR of $228,571 per QALY compared with biosimilar infliximab, with the remaining ustekinumab regimens (every eight weeks and mixed dosage) resulting in ICURs of more than $1 million per QALY. Remaining biologic therapies (adalimumab, infliximab, and vedolizumab) were also dominated or subjected to extended dominance.

The manufacturer provided correspondence to this report indicating that the drug costs with the induction dose for ustekinumab would be reimbursed by the manufacturer. Excluding the drug costs incurred from the induction dose appears to improve the ICUR for ustekinumab when compared with conventional therapy in a population experiencing an FCTO, with an ICUR of $95,442 per QALY gained, and in a population experiencing a failure of anti-TNF therapy, with an ICUR of $77,840 per QALY gained. For the mixed population, ustekinumab resulted in an ICUR of $91,260 per QALY compared with conventional therapy. Additional information is provided in APPENDIX 3.