Evaluation of stereoselective dissolution of verapamil hydrochloride from matrix tablets press-coated with chiral excipients

In most cases the modulation of the drug delivery rate from modified-release formulations is achieved with polymers also used as chiral stationary phases in liquid chromatography. It is therefore hypothesized that the interaction of the enantiomers with the excipient may lead to differentiated delivery rates from the devices for each enantiomer. This study evaluates the stereoselective dissolution of (±)-verapamil, a model racemic drug and, for this purpose, different matrix compositions, a commercial product and a particular delivery device have been considered. The delivery device, recently proposed for the delayed release of drugs, consists of an active core containing the drug, coated by compression with different types of chiral polymeric materials. The quantitative determination of verapamil enantiomers released by these systems was carried out using a stereospecific HPLC method. Hydroxypropylmethylcellulose, β-cyclodextrin, hydroxypropyl-β-cyclodextrin and cross-linked amylose did not show any stereoselective dissolution properties while pectin, galactomannan and scleroglucan seemed to give a slightly higher dissolution rate of the R, compared with the S enantiomer. It is, however, to be verified whether these small differences in the release rate of the two enantiomers detected ‘in vitro’ could lead to real ‘in vivo’ effects.