Determination of enalapril and enalaprilat by enzyme linked immunosorbent assays: application to pharmacokinetic and pharmacodynamic analysis

Pharmacology of enalapril in children: a review

Enalapril is an angiotensin-converting enzyme (ACE) inhibitor that is used for the treatment of (paediatric) hypertension, heart failure and chronic kidney diseases. Because its disposition, efficacy and safety differs across the paediatric continuum, data from adults cannot be automatically extrapolated to children. This review highlights paediatric enalapril pharmacokinetic data and demonstrates that these are inadequate to support with certainty an age-related effect on enalapril/enalaprilat pharmacokinetics. In addition, our review shows that evidence to support effective and safe prescribing of enalapril in children is limited, especially in young children and heart failure patients; studies in these groups are either absent or show conflicting results. We provide explanations for observed differences between age groups and indications, and describe areas for future research.

Model-dependent pharmacokinetic analysis of enalapril administered to healthy adult volunteers using orodispersible minitablets for use in pediatrics

Introduction

Comparative pharmacokinetic (PK) data analysis of drugs administered using developed child-appropriate and market authorized dosage formulation is sparse and is important in pediatric drug development.

Objectives

To compare and evaluate any differences in PK of enalapril administered using two treatments of child-appropriate orodispersible minitablets (ODMTs) and market authorized reference tablet formulation (Renitec^®) using PK compartment model and validated least square minimization method (LSMM) of parameter estimation.

Methods

Full profile data sets were obtained from a phase I clinical trial, whereby three treatments of enalapril, ie, reference tablets with 240 mL water (treatment A), child-appropriate ODMTs with 240 mL (treatment B), and ODMTs dispersed in the mouth with 20 mL water (treatment C), were administered to 24 healthy adult volunteers. Virtual validation analysis was conducted using R program to select accurate and precise LSMM of parameter estimation. For the selection of PK model and estimation of parameters, enalapril data were fitted with one-and two-compartment models with first order of absorption and elimination, with and without incorporated lag time parameter (tlag). The log-transformed PK parameters were statistically compared by the two-sided paired t-test with the level of significance of P<0.05.

Results

One-compartment model with first-order absorption and elimination and incorporated lag time adequately predicted concentrations of enalapril. Reciprocal of predicted concentration using iteratively reweighted LSMM was selected as the most appropriate method of parameter estimation. Comparison of PK parameters including rate constant of absorption and elimination, volume of distribution, and tlag between the three treatments showed significant difference (P=0.018) in tlag between treatments B and A only.

Conclusion

Compared with reference formulation, enalapril administered from child-appropriate ODMTs administered with 240 mL water appeared 4 minutes earlier in serum. No other differences were observed in absorption, elimination, and relative bioavailability of drug between the three treatment arms.

Pharmacokinetics and pharmacodynamics profiles of enalapril maleate in healthy volunteers following determination of enalapril and enalaprilat by two specific enzyme immunoassays

BACKGROUND AND OBJECTIVES

Most of the pharmacokinetic (PK) parameters for enalapril and enalaprilat were established following determination of the drug and its metabolite, using angiotensin converting enzyme (ACE) inhibition assays. In these methods, enalapril has to be hydrolysed to enalaprilat first and then assayed. The purpose of this study was to re-estimate the PK parameters of enalapril and enalaprilat in healthy volunteers using two specific enzyme immunoassays for enalapril and enalaprilat.

METHODS

The rate and extent of absorption of enalapril and enalaprilat from a 10-mg dose of two enalapril maleate commercial brands (Renetic and Enalapril) were estimated using a two-way-cross over design with 1-week washout period. Blood pressure was also measured at specified time intervals and correlated to enalaprilat plasma concentrations.

RESULTS

For enalapril, the AUC(o-->infinity) values (Mean+/-SD) were 450.0+/-199.5 and 479.6+/-215.6 ng h/mL, Cmax values were 313.5+/-139.6 and 310.1+/-186.6 ng/mL, Tmax values were 1.06+/-0.30 h and 1.13+/-0.22 h, and t1/2 ranged between 0.3 to 6.1 h (1.6+/-1.5) and 0.40 to 5.05 h (1.3+/-1.0), for the two brands. For enalaprilat, the AUC(o-->infinity) values were 266.9+/-122.7 and 255.9+/-121.8 ng h/ml, Cmax values were 54.8+/-29.5 and 57.2+/-29.0 ng/mL, Tmax values were 4.6+/-1.6 h and 4.3+/-1.45 h, and t1/2 ranged between 1.1 to 10.5 h (4.5+/-2.9) and 0.6 to 9.4 h (3.5+/-2.5) for the two brands.

CONCLUSIONS

Cmax values for enalapril are about 10 times those published in the literature and the rate and extent of absorption of the two brands of enalapril and their deesterification to enalaprilat following the administration of either brand were bioequivalent. Secondly, enalaprilat concentrations at 12-24 h following a single oral dose of enalapril in healthy volunteers were lower than those reported in the literature. The values reported here correlated with the return of blood pressure to predose level. Thirdly, enzyme immunoassays for enalapril and enalaprilat are better than ACE inhibition assays and can be used in bioequivalence assessment of enalapril and enalaprilat and for therapeutic drug monitoring in a clinical laboratory setting.