title: Safety of extended treatment with sapropterin dihydrochloride in patients with phenylketonuria: results of a phase 3b study.
abstract: BACKGROUND
  Phenylketonuria (PKU) results from impaired breakdown of phenylalanine (Phe) due to deficient phenylalanine hydroxylase (PAH) activity. Sapropterin dihydrochloride (sapropterin, Kuvan®) is the only US- and EU-approved pharmaceutical version of naturally occurring 6R-BH(4), the cofactor required for PAH activity. Sapropterin enhances residual PAH activity in sapropterin-responsive PKU patients and, in conjunction with dietary management, helps reduce blood Phe concentrations for optimal control. Approval was based on the positive safety and efficacy results of four international clinical studies, the longest of which was 22 weeks in duration.
  
  
  OBJECTIVE
  To evaluate the safety of long-term treatment with sapropterin in PKU subjects who participated in previous Phase 3 sapropterin trials.
  
  
  METHODS
  PKU-008 was designed as a Phase 3b, multicenter, multinational, open-label, 3-year extension trial to evaluate the long-term safety of sapropterin in patients with PKU who were classified as sapropterin responders and participated in prior Phase 3 sapropterin studies: 111 subjects aged 4-50 years completed prior studies and were subsequently enrolled in study PKU-008. Routine safety monitoring was performed at 3-month intervals and included adverse event reporting, blood Phe monitoring, clinical laboratory evaluations, physical examinations and vital sign measurements.
  
  
  RESULTS
  Average exposure during PKU-008 was 658.7±221.3 days (range, 56-953; median, 595). The average total duration of participation in multiple studies (PKU-001, PKU-003, PKU-004, and PKU-008; or PKU-006 and PKU-008) was 799.0±237.5 days (range, 135-1151). The mean sapropterin dose was 16.2±4.7 mg/kg/day. Most adverse events were considered unrelated to treatment, were mild or moderate in severity, and were consistent with prior studies of sapropterin. No age-specific differences were observed in adverse event reporting. Three subjects discontinued treatment due to adverse events that were considered possibly or probably related to study treatment (one each of difficulty concentrating, decreased platelet count, and intermittent diarrhea). No deaths were reported. Of seven reported serious adverse events, one was considered possibly related to study treatment (gastroesophageal reflux). There were no laboratory or physical examination abnormalities requiring medical interventions. For most subjects, blood Phe concentrations were consistently within target range, confirming the durability of response in subjects undergoing extended treatment with sapropterin.
  
  
  CONCLUSIONS
  Sapropterin treatment was found to be safe and well tolerated at doses of 5 to 20mg/kg/day for an average exposure of 659 days. This study supports the safety and tolerability of sapropterin as long-term treatment for patients with PKU.
authors.affiliation: Children's Memorial Hospital, Chicago, IL, USA. bburton@childrensmemorial.org
authors.forename: Barbara K
authors.initials: BK
authors.lastname: Burton
authors.forename: Maria
authors.initials: M
authors.lastname: Nowacka
authors.forename: Julia B
authors.initials: JB
authors.lastname: Hennermann
authors.forename: Mark
authors.initials: M
authors.lastname: Lipson
authors.forename: Dorothy K
authors.initials: DK
authors.lastname: Grange
authors.forename: Anupam
authors.initials: A
authors.lastname: Chakrapani
authors.forename: Friedrich
authors.initials: F
authors.lastname: Trefz
authors.forename: Alex
authors.initials: A
authors.lastname: Dorenbaum
authors.forename: Michael
authors.initials: M
authors.lastname: Imperiale
authors.forename: Sun Sook
authors.initials: SS
authors.lastname: Kim
authors.forename: Paul M
authors.initials: PM
authors.lastname: Fernhoff
mesh_terms: D000293:Adolescent; D000328:Adult; D001708:Biopterins / Q000009:adverse effects / Q000031:analogs & derivatives*; D002648:Child; D002675:Child, Preschool; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008875:Middle Aged; D010649:Phenylalanine / Q000097:blood; D010661:Phenylketonurias / Q000188:drug therapy*
chemical_list: D001708:Biopterins; D010649:Phenylalanine; C003402:sapropterin