Relative bioavailability of sapropterin from intact and dissolved sapropterin dihydrochloride tablets and the effects of food: a randomized, open-label, crossover study in healthy adults

Background: Phenylketonuria (PKU) is an autosomal recessive metabolic disorder characterized by hyperphenylalaninemia in association with neurocognitive and neuromotor impairment. Sapropterin dihydrochloride (hereafter referred to as sapropterin) administered orally as dissolved tablets is approved by the US Food and Drug Administration for hyperphenylalaninemia in patients with tetrahydrobiopterin responsive PKU.

Objectives: This study compared the relative oral bioavailability of sapropterin when administered as intact and dissolved tablets. It also assessed the effect of food on the oral bioavailability of sapropterin administered as intact tablets.

Methods: This was a randomized, open-label, 3-treatment, 6-sequence, 3-period crossover study in healthy male and female subjects. Subjects were randomized to receive single oral 10-mg/kg doses of sapropterin administered as dissolved tablets after a fast; as intact tablets after a fast; and as intact tablets with a high-calorie, high-fat meal. The 3 dosing periods were separated by a washout period of at least 7 days. In each dosing period, blood samples were obtained within 40 minutes before and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 10, 12, 18, and 24 hours after dosing. A follow-up assessment was performed 5 to 7 days after the last dosing period. The relative bioavailability of sapropterin from the 3 dosing regimens was assessed based on C(max), AUC(0-t), and AUC(0-infinity), estimated from calculated plasma tetrahydrobiopterin concentrations using a noncompartmental model. Safety assessments included physical examinations, clinical laboratory tests, and ECGs at the beginning and end of the study. Vital signs were monitored periodically during each treatment period.

Results: The study enrolled 32 healthy subjects (16 men, 16 women) with a mean (SD) age of 29.2 (9.0) years, height of 172.7 (10.0) cm, weight of 73.0 (13.9) kg, and body mass index ranging from 18 to 30 kg/m(2). Twenty-three were white, 5 African American, 2 Asian/Pacific Islander, 1 Hispanic, and 1 Native American. The estimated geometric mean ratio of AUC(0-t) for intact compared with dissolved tablets under fasting conditions was 141.24% (90% CI, 122.05-163.43), and the geometric mean ratio of AUC(0-t) for intact tablets under fed compared with fasting conditions was 143.46% (90% CI, 124.22-165.69). Nine subjects (28.1%) reported a total of 20 treatment-emergent adverse events (AEs). The most frequently reported AEs were gastrointestinal disorders (6 subjects [18.8%]) and central nervous system disorders (4 [12.5%]). Eight AEs considered possibly or probably related to sapropterin were reported by 4 subjects (12.5%); these were of mild severity and gastrointestinal in nature. No severe or serious AEs or discontinuations due to AEs occurred during the study.

Conclusions: Administration of sapropterin as intact tablets and with a high-calorie, high-fat meal was associated with increased drug exposure. Oral administration of sapropterin 10 mg/kg as intact tablets with or without food was generally well tolerated.