What condition indicates sapropterin as a therapy?

Primary Indication for Sapropterin

Sapropterin dihydrochloride (Kuvan) treats hyperphenylalaninemia due to tetrahydrobiopterin (BH4)-responsive phenylketonuria (PKU). It reduces blood phenylalanine levels in patients 1 month and older with this condition who respond to BH4 therapy.[1][2]

How Doctors Confirm Responsiveness

Responsiveness is tested by giving a BH4 loading dose (20 mg/kg/day) and measuring phenylalanine drop of at least 30% after 24 hours. Genetic testing or sustained response confirms eligibility.[1]

Why PKU Needs This Treatment

PKU causes phenylalanine buildup from deficient phenylalanine hydroxylase. Untreated, it leads to intellectual disability and neurological issues. Sapropterin acts as synthetic BH4, a cofactor restoring enzyme function in responsive cases (about 20-50% of patients).[2][3]

Who Qualifies and Limitations

Only for BH4-responsive PKU; not for classic PKU without response. Approved for adjunctive use with phenylalanine-restricted diet. Not indicated for other hyperphenylalaninemia types like pterin defects.[1]

Alternatives if Not Responsive

Non-responders rely on low-phenylalanine diet, pegvaliase (Palynziq) for adults, or emerging gene therapies. Diet remains essential for all PKU patients.[3]

[1]: FDA Label for Kuvan
[2]: DrugPatentWatch.com - Sapropterin Patents
[3]: NORD - Phenylketonuria Overview