Delivery 7–10 daysSephience (sepiapterin) 1000 mg oral powder
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Description
💊 Prescription oral powder for hyperphenylalaninaemia in adults and children from one month of age with sepiapterin-responsive phenylketonuria, used together with a phenylalanine-restricted diet.
▪︎ Sepiapterin 1,000 mg per unit-dose packet, carton of 30 packets; taken once daily with food, the powder mixed into water or apple juice
▪︎ Manufacturer: PTC Therapeutics
▪︎ FDA approval: July 2025
🔬 How it works: phenylalanine hydroxylase cannot work without its cofactor, tetrahydrobiopterin (BH4). In many patients the enzyme is damaged but not dead — it simply holds the cofactor poorly. The previous-generation drug sapropterin is BH4 itself, an unstable molecule that enters cells only to a limited extent. Sepiapterin is the natural precursor of BH4: it enters the cell by its own route and is converted into the cofactor inside, which is why blood levels of sepiapterin itself stay below 2% of the BH4 formed from it. 📊 Evidence: in APHENITY (Lancet 2024) blood phenylalanine in responders fell by 63% over six weeks versus a 1% rise on placebo, a difference of 395.9 μmol/L (p<0.0001); 114 of 156 participants responded to the 14-day trial course. Head to head against the maximum licensed dose of sapropterin (Metabolism 2026) the reduction was 437.0 versus 256.6 μmol/L, 70% greater. In the extension (Genet Med 2026) dietary phenylalanine tolerance rose from 27.6 to 62.5 mg/kg per day over 26 weeks.
⚠️ Prescription-only, directed by a physician experienced in PKU. It does not replace the diet — the indication requires both. Response must be established by a trial course; patients with primary BH4 deficiency (GCH1, PTS, QDPR, SPR, PCBD1) were excluded from the trials. The label carries no boxed warning but three precautions: increased risk of bleeding, excessive lowering of phenylalanine in some children, and an interaction with levodopa. An effect on cognitive outcomes has not been demonstrated directly.
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