Melin J, Parra-Guillen ZP, Michelet R, et al. - Researchers intended to describe the pharmacokinetics/pharmacodynamics (PK/PD) of cortisol utilizing 17-hydroxyprogesterone (17-OHP) as a biomarker among pediatric patients having congenital adrenal hyperplasia (CAH). They also evaluated different hydrocortisone dosing regimens. A PK/PD model was constructed by utilizing cortisol and 17-OHP levels from 30 CAH patients (7-17 years) taking standard hydrocortisone replacement therapy (5-20 mg) twice (n = 17) or thrice (n = 13) daily. Cortisol concentration-time profiles were perfectly defined by a two-compartment model with first-order absorption and expected high bioavailability (82.6%). Overall, experts successfully established a PK/PD model after hydrocortisone administration in this study. Also, an enhanced dosing regimen of 38% at 06:00, 22% at 12:00, 17% at 18:00 and 22% at 24:00 of the daily hydrocortisone dose was proposed. The superiority of four-times daily dosing regimen was indicated as it avoided sub-therapeutic cortisol levels and better mimicked the circadian rhythm of cortisol.