Carvedilol (CAR), a racemic lipophilic aryloxy propanolamine, acts as a selective α1-adrenoreceptor antagonist and a nonselective β-adrenoreceptor antagonist. CAR metabolism mainly produces three active metabolites: desmethyl carvedilol (DMC), 4'-hydroxy carvedilol (4'OHC) and 5'-hydroxy carvedilol (5'OHC). The oxidative S-(-)-metabolites contribute to the β-antagonistic effect, yet not to the α-antagonistic effect to be observed after drug dosage. Therefore, the three β-adrenoceptor blocking metabolites, which are structurally closely related to the parent CAR, are included into the development of a bioanalytical quantitative method for all major active species relevant with respect to adrenoceptor-blockade. Because of the given pharmacological profile, resolution of the enantiomers of carvedilol, of 4'- and 5'-hydroxy carvedilol as well as of DMC, is mandatory. The current study aims to determine the response surface for the enantiomer separation of the parent CAR as well as the major metabolites on a suitable chiral stationary phase. Design of experiment approach (DoE) was utilized in an initial screening phase followed by central-composite design for delimitation of the response surface for resolution of the four enantiomeric pairs in least run time. The impact of chromatographic variables (composition and percentage of organic modifier(s), buffer type, buffer pH, flow rate) on critical peaks resolution and adjusted retention time was evaluated, in order to select the most significant critical quality attributes. On this basis, a robust UHPLC-UV method was developed and optimized for the simultaneous, enantioselective determination of CAR along with its major active metabolites (4'OHC, 5'OHC, and DMC) on Chiralpak IBN-5. The optimized UHPLC-UV method (which includes metoprolol as the internal standard) was validated according to the ICH M10 guidelines for bioanalytical methods and proven to be linear, precise, accurate, and robust. The validated assay was applied to plasma samples from cardiovascular patients treated with rac-CAR (blood randomly drawn at different times after oral CAR intake). In order to provide more insight into the mechanism of the enantiomer separation of CAR and its metabolites on the CSP, docking experiments were performed. Molecular simulation studies suggest the chiral recognition to be mainly due to different binding poses of enantiomers of the same compound.
Keywords: active metabolites; cardiovascular patients; carvedilol; chiral separation; docking; quality-by-design.