Economic Evaluation of Stiripentol for Dravet Syndrome: A Cost-Utility Analysis

Jesse Elliott, Bláthnaid McCoy, Tammy Clifford, George A. Wells, Doug Coyle

Dravet syndrome is a catastrophic form of pediatric treatment-resistant epilepsy with few effective treatment options. Stiripentol is approved for use in Canada for treatment of Dravet syndrome, but the associated long-term costs and benefits have not been well-studied and its cost effectiveness is unclear. The aim of this study was to evaluate the cost effectiveness of stiripentol as an adjunctive treatment to clobazam and valproate for treatment of Dravet syndrome from the perspective of the Canadian public healthcare payer. A cost-utility analysis was performed to estimate the costs and quality-adjusted life-years (QALYs) associated with adjunctive stiripentol treatment compared with clobazam and valproate alone in children with Dravet syndrome. Transition probabilities, drug efficacy, utility weights, and costs were obtained from a review of the literature. Probabilistic analyses were conducted using a Markov model with health states related to seizure frequency. A 10-year horizon was used. The incremental cost per QALY gained (incremental cost-effectiveness ratio [ICER]) for adjunctive use of stiripentol was calculated, and assumptions were explored in scenario analyses. All costs are expressed in 2017 Canadian dollars ($Can). Compared with clobazam and valproate alone, the adjunctive use of stiripentol is associated with an ICER of $Can151,310. At a willingness-to-pay threshold of $Can50,000, the probability that stiripentol was the optimal treatment was 5.2%. The cost of stiripentol would need to be reduced by 61.4% for stiripentol to be cost effective. From the perspective of the Canadian public healthcare payer, stiripentol is not cost effective at its current price at a willingness-to-pay threshold of $Can50,000. Funding stiripentol will be associated with important opportunity costs that bear consideration.