Relative bioavailability of a newly developed pediatric formulation of bosentan vs. the adult formulation

What is known: Bosentan is a dual endothelin receptor antagonist approved for the treatment of pulmonary arterial hypertension (PAH). Since bosentan is frequently used to treat pediatric PAH patients, a pediatric formulation was developed. Aim: To evaluate the pharmacokinetic properties of bosentan and its active metabolite, Ro 48-5033, of the quadrisected, dispersible pediatric vs. the adult tablet after single-dose administration to healthy subjects. Secondary objectives of the study were to compare the pharmacokinetics of two inactive metabolites and the safety of both formulations. Materials and methods: In this open-label, two-way crossover study, subjects (20 - 43 years) were randomized to receive single oral doses of 62.5 mg of bosentan as 1 adult tablet and 64 mg as 2 pediatric tablets of 32 mg. Blood samples were drawn over a 48-hour period to measure bosentan and its metabolites. Results: 16 subjects were enrolled and completed the study. Following treatment with the pediatric formulation, values for C-max and AUC(0-infinity) of bosentan were lower than with the adult formulation with geometric mean ratios (90% confidence interval) of 0.82 (0.65, 1.04) and 0.87 (0.78, 0.97), respectively. Similar results were obtained for the primary active metabolite Ro 48-5033. Both treatments were well tolerated. What is new and conclusion: Although the 90% confidence intervals of the geometric mean ratios of C-max and AUC(0-infinity) were not entirely within the conventional bioequivalence range (0.80 - 1.25), no clinically relevant effect of formulation on the pharmacokinetics of bosentan and Ro 48-5033 was detected. Both formulations were well tolerated.