The manufacturer’s submission provided an economic model in which GPB does not appear, at a willingness-to-pay threshold of $50,000 per QALY, to be cost-effective when compared with either the existing pharmaceutical option (NaPBA; Pheburane) or dietary control. The CDR analysis of this model identified many flaws, although most of the fixable flaws do not appear to substantially affect the incremental cost-effectiveness ratios, when accounted for. The exception to this was modifying the simulated relationship between short-term ammonia levels and HACs.

While the changes to the model affect estimates of cost-effectiveness, GPB does not appear to be cost-effective at a willingness-to-pay cost-effectiveness threshold of $50,000 per QALY, or at four times this figure ($200,000 per QALY). Overall, the ICURs produced in the four subgroups of interest range from $1 million per QALY to $2.55 million per QALY.

In order for the incremental cost-effectiveness of GPB to even approach small multiples of $50,000 per QALY, it appears that significant price reductions would be necessary. For the analyses comparing GPB with NaPBA, price reductions of more than 30% would be required for GPB to reach an ICUR of $200,000 per QALY. For the analyses comparing GPB with dietary control, higher price reductions of more than 50% would be required.

The manufacturer assumed that patients were treated over a lifetime and that the effect of treatment was maintained during this period. If this maintenance of effect is not accurate, this would have overestimated the ICURs in favour of GPB. In addition, a stopping rule for treatment was not implemented. The direction of the impact of such a rule on the cost-effectiveness results is unknown.

The price of GPB is 46% higher than the price of NaPBA (Pheburane).