Relyvrio, the fixed-dose combination of sodium phenyl-butyrate and taurursodiol that received accelerated approval for treatment of amyotrophic lateral sclerosis (ALS) in 2022 based on a phase 2 trial showing that it slowed functional decline, has voluntarily been withdrawn from the market. According to the manufacturer (Amylyx), the decision to withdraw Relyvrio was based on the results of a phase 3, 48-week trial (PHOENIX). The change from baseline on the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale, which measures fine motor, gross motor, bulbar, and respiratory functioning, was not statistically significantly greater with Relyvrio than with placebo. Patients who are already taking the combination will be able to receive the drug from the manufacturer free of charge.

Tofersen (Qalsody – Biogen), an intrathecally administered antisense oligonucleotide, has received accelerated approval from the FDA for treatment of amyotrophic lateral sclerosis (ALS) in adults who have a mutation in the superoxide dismutase 1 (SOD1) gene. About 2% of patients with ALS have mutations in the SOD1 gene. Tofersen is the first drug to be approved in the US that targets a genetic cause of ALS. Accelerated approval of the drug was based on the surrogate endpoint of a reduction in plasma neurofilament light chain, which is considered likely to predict clinical benefit.

The FDA has approved Relyvrio (Amylyx), a fixed-dose combination of sodium phenylbutyrate and taurursodiol, for treatment of amyotrophic lateral sclerosis (ALS). Sodium phenylbutyrate (Buphenyl, and others) has been available by prescription for years for treatment of urea cycle disorders. Taurursodiol (tauroursodeoxycholic acid), a derivative of ursodiol, is an over-the-counter bile acid supplement claimed to have neuroprotective benefits. Relyvrio is the third drug to be approved in the US for treatment of ALS; riluzole (Rilutek, and others) and edaravone (Radicava, Radicava ORS) were approved earlier.

The FDA has approved an oral liquid formulation of glycerol phenylbutyrate (Ravicti – Hyperion) for chronic management of patients ≥2 years old with urea cycle disorders that cannot be adequately managed by a protein- restricted diet. Sodium phenylbutyrate (Buphenyl, and generics), another oral drug approved by the FDA for this indication, has a bitter taste. The new product, which contains no sodium, has little or no taste. Either drug must be used in addition to a protein-restricted diet and, if needed, dietary supplementation with amino acids and other nutrients.