CONTEXT AND OBJECTIVE: This study aimed at comparing pharmacokinetics of two different doses of hydrocortisone (HC) in patients with secondary adrenal insufficiency (SAI).
DESIGN, SETTING AND PATIENTS: Forty-six patients with SAI participated in this randomized double-blind crossover study.
INTERVENTION: Patients received two different doses of HC (0.2-0.3mg HC/kg body weight/day and 0.4-0.6mg HC/kg body weight/day).
MAIN OUTCOME MEASURES: One- and two-compartment population models for plasma free cortisol, plasma total cortisol and salivary cortisol were parameterized. The individual pharmacokinetic parameters clearance (CL), volume of distribution (Vd), elimination half-life (t1/2), maximum concentration (Cmax), and area under the curve (AUC) were calculated.
RESULTS: The one-compartment models gave a better description of the data compared to the two-compartment models. Weight-adjusted dosing reduced variability in cortisol exposure with comparable AUCs between weight groups. However, there was large inter-individual variation in CL and Vd of plasma free cortisol, plasma total cortisol and salivary cortisol. As a consequence, AUC24h varied more than 10 fold. Cortisol exposure was increased with the higher dose, but this was dose proportional only for free cortisol concentrations and not for total cortisol.
CONCLUSIONS: Cortisol concentrations after a doubling of the dose were only dose proportional for free cortisol. HC pharmacokinetics can differ up to 10-fold inter-individually and individual adjustment of treatment doses may be necessary. Doubling of the HC dose in fast metabolizers (patients that showed relative low AUC and thus high clearance compared to other patients), does not result in significantly enhanced exposure during large parts of the day and these patients may need other management strategies.