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Plasma Concentrations of Tadalafil in Children With Pulmonary Arterial Hypertension

Hiroyuki Kohno, Fukiko Ichida, Keiichi Hirono, Sayaka Watanabe Ozawa, Naoki Yoshimura, Tsuneyuki Nakamura, Chisato Akita, Kazuya Ishida et al.

Therapeutic Drug Monitoring, 2014

23 participants · 16 citations

Abstract

BACKGROUND: There is no report documenting the plasma concentrations of tadalafil in children. This study was performed to evaluate the variability in the pharmacokinetics of tadalafil in children with pulmonary arterial hypertension (PAH) treated routinely with the drug. METHODS: Plasma samples were taken twice (post- and predose) after repetitive oral administration, and the pharmacokinetic parameters (CL/F and V/F) in individual patients were estimated by the Bayesian method using the nonlinear mixed effects model. We also determined the unbound concentration of tadalafil using ultrafiltration. RESULTS: Tadalafil was administered to 23 children aged between 0.25 and 17.4 years, with a mean age of 3.58 years. The mean (±SD) daily dose of tadalafil was 0.97 ± 0.41 mg/kg. Sixteen of the 23 children received bosentan concomitantly. The mean CL/F and V/F values of tadalafil were 0.149 L·h-1·kg-1 and 1.87 L/kg, respectively, which were higher than those reported in adults. No effects of age, bosentan, or the estimated glomerular filtration rate were observed on the CL/F value, indicating that other residual factors might account for the interindividual variability among children with PAH. The unbound tadalafil concentrations of the postdose samples ranged from 5.9 to 146 (46.9 ± 37.1) nmol/L, higher than the reported IC50 value of this phosphodiesterase-5 drug for humans (2-4 nmol/L, corresponding to 0.8-1.6 ng/mL). CONCLUSIONS: We demonstrated variability in the total and…

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