OBJECTIVES : To assess the 5-year budget impact of single-dose gene-replacement therapy AVXS-101 (onasemnogene abeparvovec) versus current standard-of-care (nusinersen) in US patients with Spinal Muscular Atrophy Type 1 (SMA1).

METHODS : We developed a multi-state survival Markov model with health-state transitions based on milestone attainment (sitting, walking) from published clinical trials. Survival benefit was estimated using long-term survival data from sitting and walking SMA patients and natural history data. We used published sources to estimate the size of eligible population and expected market share of each therapy before and after AVXS-101 approval. Costs related to drug acquisition and administration, expected hospital markups, adverse events and SMA care were sourced from published claims analysis data, literature, and expert opinion. AVXS-101 drug costs were assessed at hypothetical price points from $2M to $3M.

RESULTS : For a US payer covering 1,000,000 individuals/year, an average of 0.68 SMA1 patients would be treated annually. At $2M AVXS-101 price point, the 5-year per-member-per-month (PMPM) budget impact of adding AVXS-101 to the formulary was $0.05 (at a $3M price point: $0.11). The PMPM impact decreased from $0.08 in year 1 to $0.03 in year 5 at $2M AVXS-101 price (from $0.14 to $0.08 at $3M price). Regardless of price point, adding AVXS-101 to the formulary resulted in a -$15K offset of SMA care costs in the fifth year.

CONCLUSIONS : Depending on price point, addition of AVXS-101 to a payer’s formulary would result in a 5-year PMPM budget impact of $0.05 to $0.11. The budget impact decreases each year as single-dose therapy precludes long-term acquisition and administration costs of treating prevalent patients. Inclusion of AVXS-101 on a formulary is estimated to offset payers’ SMA care costs by -$15K by the fifth year. Additionally, installment plan for AVXS-101 payments will reduce the budget impact further.