Main Populations in Sapropterin Trials
Sapropterin (Kuvan), approved for phenylketonuria (PKU), was tested primarily in patients with hyperphenylalaninemia due to tetrahydrobiopterin (BH4)-responsive PKU. Pivotal trials like PKU-004 and PKU-005 enrolled children and adults aged 4+ years with baseline blood phenylalanine (Phe) levels between 10-30 mg/dL (or 361-1,082 μmol/L). These studies required a positive response to sapropterin, defined as ≥30% Phe reduction after an 8-day challenge.[1][2]
Trials in Young Children
PKU-006 focused on children aged 0-4 years with Phe levels 6-30 mg/dL. Of 89 enrolled infants and toddlers, 61 showed responsiveness (≥30% Phe drop). Long-term extension data confirmed sustained Phe control in this group, supporting pediatric approval down to 1 month old.[1][3]
Adults and Older Patients
Adult data came from PKU-004 extensions and PKU-018, including patients up to age 50+ with similar Phe criteria. Responders (about 20-50% across studies) maintained lower Phe levels over 2-6 years. Trials excluded severe, untreated PKU cases unresponsive to BH4.[2][4]
What About Non-Responders or Other Conditions?
Around 20-30% of PKU patients do not respond, based on screening trials like PKU-001 (n=363 children). Sapropterin is not indicated for BH4-deficient hyperphenylalaninemia or primary liver disease. No trials targeted pregnant women or neonates under 1 month.[1][5]
Trial Sizes and Demographics
| Trial | Age Group | N Enrolled | % Responders | Key Inclusion |
|-------|-----------|------------|--------------|--------------|
| PKU-001 | 0-18 years | 363 | 56% screened positive | Phe 12.5-30 mg/dL |
| PKU-004 | 8+ years | 245 | 51% | Phe 10-30 mg/dL |
| PKU-005 | 4-12 years | 90 | 62% | Phe >10.5 mg/dL |
| PKU-006 | 0-4 years | 89 | 69% | Phe 6-30 mg/dL[1][2] |
Sources
[1]: FDA Label for Kuvan
[2]: BioMarin Clinical Data Summary
[3]: Trefz et al., Mol Genet Metab 2009;96:22-8
[4]: Burton et al., Mol Genet Metab 2007;92:239-47
[5]: DrugPatentWatch.com - Sapropterin Clinical Overview