Population Pharmacokinetic Analysis of Enalapril and Enalaprilat in Newly Treated Children with Heart Failure: Implications for Safe Dosing of Enalapril (LENA Studies)

Background: Enalapril orodispersible minitablets (ODMT) have been authorised by the European Medicines Agency for the treatment of heart failure in children from birth to 17 years of age in 2023. Consequently, the use of enalapril in very young and angiotensin-converting enzyme inhibitor (ACEi) naïve patients is expected to increase. Objectives: Simultaneous characterisation of the pharmacokinetics (PK) of enalapril and the active metabolite enalaprilat in ACEi naïve children with heart failure using a combined population pharmacokinetic (PopPK) model and identification of clinically relevant covariates for the dosing of enalapril in this population. Methods: Data of ACEi naïve subjects from the European project ‘Labeling of Enalapril from Neonates up to Adolescents’ (LENA) were analysed using nonlinear mixed effects modelling. In the prospective, open-label, multicentre phase II/III PK bridging studies, children with heart failure due to dilated cardiomyopathy (DCM) and congenital heart disease (CHD) received enalapril ODMT according to an age- and weight-dependent dosing regimen. Allometric scaling was implemented for the disposition parameters of enalapril and enalaprilat. Stepwise covariate modelling was used to test the covariates age, sex, serum creatinine and Ross score. The final model was validated using nonparametric bootstrap analysis. Simulations were performed to assess the impact of the covariates after the first dose and at steady state. Results: The analysed dataset comprised 173 enalapril and 268 enalaprilat serum concentrations from 34 subjects aged 25 days to 2.1 years (median age = 0.3 years). A combined model consisting of a one-compartment model for enalapril coupled with a one-compartment model for enalaprilat with absorption lag was selected as the structural model. Covariate analysis revealed that the weight-adjusted apparent clearance of enalaprilat increases with increasing age and decreases with increasing serum creatinine. In addition, the weight-adjusted apparent volume of distribution of enalaprilat decreases with increasing Ross score. The simulations indicated that serum creatinine levels above the normal reference range, age and weight were clinically relevant covariates for both the first dose and the steady state dose of enalapril. Furthermore, the simulations indicated that the Ross score is a clinically relevant covariate for the first dose of enalapril. Conclusions: The results of the PopPK analysis and simulations indicated that, in addition to the currently considered parameters of weight and renal function, the parameters of age and severity of heart failure should also be considered when dosing enalapril in children with heart failure. Trial Registration: Trial registration number (date of registration): EudraCT 2015-002335-17 (30 November 2015), EudraCT 2015-002396-18 (30 November 2015). The trials were registered on the EU Clinical Trials Register (https://www.clinicaltrialsregister.eu).