Kuvan® in Phenylketonuria Patients Less Than 4 Years Old

• Kuvan® (Drug), also known as Sapropterin dihydrochloride: Kuvan® (sapropterin dihydrochloride) tablets will be administered orally at the dose of 10 mg/kg/day and will be escalated to 20 mg/kg/day if after 4 weeks a subject's Phe tolerance is not increased by at least 20% versus baseline.
• Phenylalanine (Phe)-restricted diet (Other): Phe intake will be adjusted every 2 weeks, based on the mean Phe levels of the previous 2 weeks using pre-defined Phe adjustment criteria.

Primary outcomes

• Dietary Phenylalanine (Phe) Tolerance at Week 26 [Week 26]: Phe tolerance was defined as the amount of dietary Phe prescribed (milligram per kilogram per day \[mg/kg/day\]) while maintaining blood Phe levels within the selected therapeutic target range (defined as greater than or equal to \[>=\] 120 to less than \[<\] 360 micromoles per liter \[mcmol/L\]).

Secondary outcomes

• Mean Blood Phe Levels [Baseline, Weeks 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, and 26]: Mean blood phe levels were defined as the mean of blood phe levels assessed over each 2-week intervals
• Change From Baseline in Dietary Phe Tolerance After 26 Weeks [Baseline and at Week 26 (last observation carried-forward [LOCF])]: Phe tolerance was defined as the amount of dietary Phe ingested (mg/kg/day) while maintaining blood Phe levels within the selected therapeutic target range (defined as >=120 to <360 mcmol/L).
• Number of Subjects With Any TEAEs, AEs Related to Kuvan, Serious AEs, AEs Leading to Death, and AEs Leading to Discontinuation [From the first dose of study drug administration up to 31 days after the last dose of study drug administration]: An AE was defined as any new untoward medical occurrences/worsening of pre-existing medical condition without regard to possibility of causal relationship. A serious adverse event (SAE) was an AE that resulted in any of the following outcomes: death; life threatening; persistent/significant disability/incapacity; initial or prolonged inpatient hospitalization; congenital anomaly/birth defect. Treatment-emergent are events between first dose of study treatment and up to 31 days after last dose that were absent before treatment or that worsened relative to pretreatment state.
• Number of Subjects With Normal Neuromotor Developmental Milestones Assessed Using Denver Developmental Scale (DDS) [Baseline, Weeks 12, 26]: Subjects with normal neuromotor development were assessed by standardized developmental milestones using a parent/guardian report form in the following areas: fine motor, gross motor, language, and personal-social using DDS Test. DDS Test is a widely used to examine the developmental progress of 0-6 years of children. The scale reflects what percentage of a certain age group is able to perform a certain task. Tasks are grouped into 4 categories (social contact, fine motor skill, language, and gross motor skill) and include items such as smiles spontaneously (performed by 90% of three-month-olds), knocks 2 building blocks against each other (90% of 13-month-olds), speaks 3 words other than "mom" and "dad" (90% of 21-month-olds), or hops on 1 leg (90% of 5-year-olds). The more items a child fails to perform (passed by 90% of his/her peers), the more likely the child manifests a significant developmental problems.
• Neurodevelopmental Status Assessed Using Bayley III Scales of Infant and Toddler Development [Baseline and Week 26]: Neurodevelopmental assessments was done using the following age-dependent scales: Bayley III for subjects less than (<) 3.5 years of age and WPPSI III for subjects greater than or equal to (>=) 3.5 to <4 years of age, based on following scores: adaptive behavior composite (ABC) score, cognitive composite (CC) score, language composite (LC) score, motor composite (MC) score., and social-emotional composite (SEC) score. Composite scores ranged from 40 (very poor) to 160 (excellent) and are classified as following: >=115: accelerated performance; 85-114: development within normal limits; 70-84: mildly delayed development; less than or equal to (<=) 69: significant delayed development.
• Growth Parameters Standard Deviation Scores (SDS) [Baseline, Weeks 4, 8, 12, 16, 20, and 26]: Growth assessment was performed by monitoring body mass index, height (or length), weight, and maximal occipital-frontal head circumference (MOFHC). Supine length was measured up to 2 years of age thereafter standing height was measured unless subject was unable to stand upright, in which case supine length was measured. Respective parameter SDS was calculated as the value of parameter minus reference mean value of parameter divided by standard deviation of the reference population.
• Number of Subjects With Hypophenylalanemia [Week 26]: Hypophenylalanemia is defined as the condition of blood Phe levels <120 mcmol/L.
• Dietary Phe Tolerance During Extension Period [Every 6 months during 3 year extension period or until product is commercially approved]: Phe tolerance was defined as the amount of dietary Phe ingested (mg/kg/day) while maintaining blood Phe levels within the selected therapeutic target range (defined as >=120 to <360 mcmol/L).
• Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP) [Baseline, Weeks 4, 8, 12, 16, 20, and 26]
• Number of Samples With Phenylalanine Hydroxylase (PAH) Gene Mutations [Screening (within 42 days prior to Day 1 of the 26-week study period)]: The DNA samples received were quantified by using a nanophotometer, and were aliquoted to a concentration of 20 nanogram/microliter DNA and aliquots from each sample were distributed to one 96-well plate. All samples were Sanger sequenced regarding exons 1 to 13 of the PAH gene in forward direction using the DNAs in the 96-well plate. All samples showing variants were Sanger sequenced regarding the concerned exon in reverse direction using DNA from the original tube. All samples showing a homozygous mutation were analyzed by MLPA. All samples showing only 1 mutation were analyzed by MLPA. All samples showing only 1 or no mutation were resequenced completely (exons 1 to 13) in both directions.
• Population Pharmacokinetic (PK) Parameter: Apparent Clearance (CL/f) [Weeks 5 to 12]: CL/f is the rate at which a drug is removed from the body via renal, hepatic and other clearance pathways.The reason for pooling subjects receiving Kuvan and subjects with Phe-restricted Diet was to facilitate the estimation of baseline endogenous value of BH4 which can only be observed in subjects not receiving the treatment. Ignoring this baseline endogenous value would have led to biased stimated of the Kuvan PK parameters. This pooling assumes that the addition of Kuvan does not confound the BH4 measurements in these analyses as a consequence the population PK parameters describing the PK of BH4 are the same for the 2 arms and so cannot be presented in terms of per arm/per treatment group based as per the planned analysis.
• Population PK Parameter: Apparent Volume of Distribution (V/f) [Weeks 5 to 12]: V/f is defined as the distribution of a medication between the plasma and the rest of the body after the dose. It is the theoretical volume in which the total amount of drug would need to be uniformly distributed to produce the desired blood concentration of the drug. The reason for pooling subjects receiving Kuvan and subjects with Phe-restricted Diet was to facilitate the estimation of baseline endogenous value of BH4 which can only be observed in subjects not receiving the treatment. Ignoring this baseline endogenous value would have led to biased stimated of the Kuvan PK parameters. This pooling assumes that the addition of Kuvan does not confound the BH4 measurements in these analyses as a consequence the population PK parameters describing the PK of BH4 are the same for the 2 arms and so cannot be presented in terms of per arm/per treatment group based as per the planned analysis.
• Population PK Parameter: Area Under the Plasma Concentration Curve, Time 0 to Infinity (AUC [0-infinity]) [Weeks 5 to 12]: AUC \[0-infinity\] was estimated by determining total area under the curve of the concentration versus time curve extrapolated to infinity. Since AUC could not be obtained from non-compartmental analysis because of sparse data, AUC = Dose/(CL/F); CL/F was population apparent clearance estimated from the population PK model, \& Dose the actual total dose received by the patient on one dosing interval. The reason for pooling subjects receiving Kuvan \&subjects with Phe-restricted Diet was to facilitate estimation of baseline endogenous value of BH4 which can only be observed in subjects not receiving treatment. Ignoring this baseline endogenous value would have led to biased estimated of Kuvan PK parameters. This pooling assumes that the the addition of Kuvan does not confound the BH4 measurements in these analyses as a consequence the population PK parameters describing the PK of BH4 were same for the 2 arms and cannot be presented per arm/per treatment group as per planned analysis.
• Population PK Parameter: Terminal Elimination Half-life (t1/2) [Weeks 5 to 12]: The t1/2 was defined as the time required for plasma concentration of drug to decrease 50 percent (%) in the final stage of elimination. Since t1/2 could not be obtained from non-compartmental analysis because of sparse data, t1/2 was estimated as Log(2)*(V/F)/(CL/F), where V/F \& CL/F were the population apparent central Volume \& clearance, estimated from population PK model. The reason for pooling subjects receiving Kuvan \& subjects with Phe-restricted Diet was to facilitate the estimation of baseline endogenous value of BH4 which can only observed in subjects not receiving treatment. Ignoring this baseline endogenous value would have led biased stimated of the Kuvan PK parameters. This pooling assumes that the addition of Kuvan does not confound the BH4 measurements in these analyses as a consequence the population PK parameters describing the PK of BH4 are the same for the 2 arms and so cannot be presented in terms of per arm/per treatment group based as per the planned analysis.
• Population PK Parameter: Maximum Observed Plasma Concentration (Cmax) [Up to Week 26]
• Population PK Parameter: Time to Maximum Plasma Concentration (Tmax) [Up to Week 26]

Sex: All, ages: any to 4 Years

Inclusion Criteria:

* Male or female PKU infants and young children less than (<) 4 years of age at the scheduled Day 1 visit of the 26-week study period (taking into consideration the maximum of 21 days in the screening period)
* Confirmed clinical and biochemical PKU, including at least two previous blood Phe levels greater than or equal to (>=) 400 micromol per liter (mcmol/L) obtained on 2 separate occasions
* Previously responded, as assessed by the Investigator, to a tetrahydrobiopterin (BH4) test, if all 3 of the following criteria are satisfied:

  1. The BH4 dose was 20 milligram per kilogram per day (mg/kg/day)
  2. The duration of the test was at least for 24 hours
  3. A 30% decrease in blood Phe levels.
* Defined level of dietary Phe tolerance consistent with the diagnosis of PKU
* Good adherence to dietary treatment, including prescribed dietary Phe restriction and prescribed amounts of Phe-free protein supplements and low-Phe foods
* Maintenance of blood Phe levels within the therapeutic target range of 120-360 mcmol/L (defined as >=120 to <360 mcmol/L) over a 4-month period prior to Screening, as assessed by the Investigator
* Parent(s) and/or guardian(s) willing to comply with all study procedures, maintain strict adherence to the diet, and willing and able to provide written, signed informed consent after the nature of the study has been explained and prior to any study procedures

Exclusion Criteria:

* Use of Kuvan®, Biopten®, or any unregistered preparation of tetrahydrobiopterin within the previous 30 days, unless for the purposes of a BH4 responsiveness test
* Previous exposure to Kuvan®, Biopten®, or any unregistered preparation of tetrahydrobiopterin for greater than (>)30 days
* Known hypersensitivity to Kuvan® or its excipients
* Known hypersensitivity to other approved or non-approved formulations of tetrahydrobiopterin
* Previous diagnosis of BH4 deficiency
* Current use of methotrexate, trimethoprim, or other dihydrofolate reductase inhibitors
* Current use of medications that are known to affect nitric oxide synthesis, metabolism or action
* Current use of levodopa
* Current use of experimental/other investigational or unregistered drugs that may affect the study outcomes
* Inability to comply with study procedures
* Inability to tolerate oral intake
* History of organ transplantation
* Concurrent disease or condition that would interfere with study participation or increase the risk for adverse events, including seizure disorders, corticosteroid administration, active malignancy, diabetes mellitus, severe congenital heart disease, renal or hepatic failure
* Other significant disease that in the Investigator's opinion would exclude the subject from the trial
* Any condition that, in the view of the Principal Investigator renders the subject at high risk for failure to comply with treatment or to complete the study

Participant flow

Outcome results

• Dietary Phenylalanine (Phe) Tolerance at Week 26 (Primary), Mean, mg/kg/day: Kuvan® + Phe-restricted Diet 80.6 +/- 4.2; Phe-restricted Diet 50.1 +/- 4.3
• Mean Blood Phe Levels (Secondary), Mean, micromol per liter (mmol/L): Kuvan® + Phe-restricted Diet 287.3 +/- 166.6; Phe-restricted Diet 352.9 +/- 219.9
• Change From Baseline in Dietary Phe Tolerance After 26 Weeks (Secondary), Mean, mg/kg/day: Kuvan® + Phe-restricted Diet 37.1 +/- 17.3; Phe-restricted Diet 35.8 +/- 20.9
• Number of Subjects With Any TEAEs, AEs Related to Kuvan, Serious AEs, AEs Leading to Death, and AEs Leading to Discontinuation (Secondary), Number, subjects: Kuvan® + Phe-restricted Diet 27; Phe-restricted Diet 27
• Number of Subjects With Normal Neuromotor Developmental Milestones Assessed Using Denver Developmental Scale (DDS) (Secondary), Number, subjects: Kuvan® + Phe-restricted Diet 18; Phe-restricted Diet 21
• Neurodevelopmental Status Assessed Using Bayley III Scales of Infant and Toddler Development (Secondary), Mean, Units on a scale: Kuvan® + Phe-restricted Diet 106.5 +/- 14.2; Phe-restricted Diet 96.2 +/- 14.6
• Growth Parameters Standard Deviation Scores (SDS) (Secondary), Mean, SDS: Kuvan® + Phe-restricted Diet 0.37 +/- 0.84; Phe-restricted Diet 0.34 +/- 0.99
• Number of Subjects With Hypophenylalanemia (Secondary), Number, Subjects: Kuvan® + Phe-restricted Diet 10; Phe-restricted Diet 9
• Dietary Phe Tolerance During Extension Period (Secondary)
• Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP) (Secondary), Mean, mmHg: Kuvan® + Phe-restricted Diet 93.5 +/- 11.0; Phe-restricted Diet 93.1 +/- 14.4
• Number of Samples With Phenylalanine Hydroxylase (PAH) Gene Mutations (Secondary), Number, Sample: Pharmacogenetic Evaluation 73
• Population Pharmacokinetic (PK) Parameter: Apparent Clearance (CL/f) (Secondary), Mean, liter per hour: Population PK Analysis Set 2780 +/- 2
• Population PK Parameter: Apparent Volume of Distribution (V/f) (Secondary), Mean, liter: Population PK Analysis Set 3870 +/- 5.9
• Population PK Parameter: Area Under the Plasma Concentration Curve, Time 0 to Infinity (AUC [0-infinity]) (Secondary), Mean, microgram*hour per liter(mcg*hour/liter): Population PK Analysis Set: Age Group 1 (< 1 Year) 234.89 +/- 89.82; Population PK Analysis Set: Age Group 2 (1 to 2 Years) 215.74 +/- 63.88; Population PK Analysis Set: Age Group 2 (>= 2 Years) 206.22 +/- 103.24
• Population PK Parameter: Terminal Elimination Half-life (t1/2) (Secondary), Number, hours: Population PK Analysis Set 0.96
• Population PK Parameter: Maximum Observed Plasma Concentration (Cmax) (Secondary)
• Population PK Parameter: Time to Maximum Plasma Concentration (Tmax) (Secondary)

Adverse events

Time frame: From the first dose of study drug administration up to 31 days after the last dose of study drug administration

Serious adverse events by term

Other adverse events by term

• Results publication: Muntau AC, Burlina A, Eyskens F, Freisinger P, Leuzzi V, Sivri HS, Gramer G, Pazdirkova R, Cleary M, Lotz-Havla AS, Lane P, Alvarez I, Rutsch F. Long-term efficacy and safety of sapropterin in patients who initiated sapropterin at < 4 years of age with phenylketonuria: results of the 3-year extension of the SPARK open-label, multicentre, randomised phase IIIb trial. Orphanet J Rare Dis. 2021 Aug 3;16(1):341. doi: 10.1186/s13023-021-01968-1. PMID 34344399
• Results publication: Muntau AC, Burlina A, Eyskens F, Freisinger P, De Laet C, Leuzzi V, Rutsch F, Sivri HS, Vijay S, Bal MO, Gramer G, Pazdirkova R, Cleary M, Lotz-Havla AS, Munafo A, Mould DR, Moreau-Stucker F, Rogoff D. Efficacy, safety and population pharmacokinetics of sapropterin in PKU patients <4 years: results from the SPARK open-label, multicentre, randomized phase IIIb trial. Orphanet J Rare Dis. 2017 Mar 9;12(1):47. doi: 10.1186/s13023-017-0600-x. PMID 28274234

• Ignacio Alvarez, MD, Study director, BioMarin Pharmaceutical

NIH grants: 2009