Pharmaceutical compositions comprising sepiapterin and uses thereof

A method of treating a tetrahydrobiopterin-related disorder selected from tetrahydrobiopterin deficiency and phenylketonuria in a subject in need thereof, the method comprising administering to the subject an effective amount of a pharmaceutical composition comprising an effective amount of sepiapterin and a pharmaceutically acceptable carrier,

• wherein the relative amount of antioxidant to sepiapterin is between 0 and 20% wt/wt;
• wherein the antioxidant, when present, is ascorbic acid, an ester of ascorbic acid, or a salt of ascorbic acid;
• and
• wherein from about 2.5 mg sepiapterin per kilogram of body weight of the subject (mg/kg) to about 150 mg/kg is administered.