The U.S. Food and Drug Administration (FDA) has approved Nulibry (fosdenopterin) to treat children with molybdenum cofactor deficiency type A.

Molybdenum cofactor deficiency type A is a rare and often fatal metabolic disorder. It often presents in the first few days of life with seizures and severe neurological/neuromuscular dysfunction.  

Babies with molybdenum cofactor deficiency type A cannot produce cyclic pyranopterin monophosphate (cPMP) which leads to a buildup of s-sulfocysteine, a neurotoxic metabolite of sulfite.  Fosdenopterin replaces the missing cPMP.

The approval was largely based on a clinical trial showing 3 year survival rates of 84% in children receiving fosdenopterin (n=13) compared to untreated children with molybdenum cofactor deficiency type A (n=18).

The most common side effects included complications related to the intravenous line, fever, respiratory infections, vomiting, gastroenteritis, and diarrhea.

Phototoxicity is a concern based on animal studies so children taking fosdenopterin should avoid exposure to sunlight and wear sunscreen, protective clothing, and sunglasses when exposed to the sun.

Since the drug is applicable to pediatric populations, the developer, Origin Biosciences, received a Rare Pediatric Priority Review Voucher.  This voucher allows the company giving a therapy under review by the FDA to have priority review. In other words, the FDA will have to review the medicine within 6 months instead of 10 months. For small companies like Origin Biosciences, this voucher is often sold to another company.  Recently, Eiger Biopharmaceuticals sold their review voucher for $95 million.  

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