Introduction: Desmopressin is used for nocturnal enuresis treatment in children. In this study, we investigated the pharmacokinetics of two formulations: a tablet and a lyophilisate, in both fasted and fed children.Methods: Previously published data from two studies (22 children aged 6 to 16 yr and 25 children aged 6 to 13 yr) were analyzed using population pharmacokinetic modeling. A 1-compartment model with first order absorption was fitted to the data. Covariates were selected using a forward selection procedure. The final model was evaluated, and sensitivity analysis was performed to improve future sampling designs. Simulations were subsequently performed to further explore the relative bioavailability of both formulations and the food effect.Results: The final model described the desmopressin plasma concentrations adequately.Formulation and fed state were included as covariates on the relative bioavailability. The lyophilisate was on average 32.1 % more available than the tablet, and fasted children exhibited an average increase in relative bioavailability of 101%, compared to fed children. Body weight was included as a covariate on distribution volume, using a power function with exponent 0.402.Simulations suggest both the formulation and the food effect are clinically relevant.
Conclusions:Bioequivalence data of two formulations of the same drug in adults, cannot be readily extrapolated to children. This is the first study in children suggesting that the two desmopressin formulations in children are not bioequivalent at the currently approved dose levels.Furthermore, the effect of food intake was found to be clinically relevant. Sampling times for a future study were suggested. This sampling design should result in more informative data and consequently generate a more robust model.
Key points Population pharmacokinetic modeling was applied to pediatric desmopressin PK data and used to extract more information out of existing pediatric drug data, generate new information and improve the collection of future information. In this study it was found that the established bioequivalence of desmopressin in adults might be different in the pediatric population. A profound food effect was also quantified. In order to make solid conclusions regarding desmopressin efficacy in children, PK and PD data should be gathered simultaneously in a well-designed study, for which some design suggestions are presented in this paper.
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