Primary Disease Treated with Sapropterin
Sapropterin dihydrochloride (Kuvan) manages phenylketonuria (PKU), a genetic disorder where the body can't break down phenylalanine, leading to toxic buildup.[1] It's approved for adults and children over 4 with hyperphenylalaninemia due to tetrahydrobiopterin (BH4)-responsive PKU, reducing blood phenylalanine levels when used with a low-phenylalanine diet.[2]
How Sapropterin Works in PKU
It acts as synthetic BH4, a cofactor for phenylalanine hydroxylase, restoring enzyme function in responsive patients. About 20-30% of PKU patients respond, confirmed by a trial dose.[3]
Testing Responsiveness Before Starting
Doctors give a 24-48 hour sapropterin challenge while monitoring phenylalanine levels. A 30% drop qualifies patients for ongoing use, up to 20 mg/kg daily.[4]
Alternatives if Not Responsive
Non-responders rely on strict dietary phenylalanine restriction, large neutral amino acid supplements, or pegvaliase (Palynziq) injections for adults.[5]
Common Side Effects Patients Report
Headache, runny nose, sore throat, and abdominal pain occur in trials, with rare serious risks like anaphylaxis from pegvaliase comparison.[6] Long-term use shows good tolerability in responsive PKU patients.
[1]: FDA Label for Kuvan
[2]: BioMarin Pharmaceuticals - Kuvan Overview
[3]: New England Journal of Medicine - Sapropterin Trial (2007)
[4]: American College of Medical Genetics PKU Guidelines
[5]: Pegvaliase FDA Approval Summary
[6]: Kuvan Clinical Safety Data