Multidimensional on-line sample preparation of verapamil and its metabolites by a molecularly imprinted polymer coupled to liquid chromatography-mass spectrometry.

A new molecularly imprinted polymer (MIP) material was synthesized selective for verapamil and utilized for on-line metabolic screening of this common calcium antagonist in biological samples. Since some metabolites of verapamil have also shown pharmacological properties, a selective and sensitive sample preparation approach that provides a metabolic profile in biologically relevant samples is important. The MIP material was coupled on-line to a restricted access material (RAM) precolumn. The multidimensional nature of this set-up removed large matrix interferents such as proteins from the sample, while the selectivity of the MIP enabled further cleanup of the smaller analytes. The selectivity and extraction efficiency of the MIP for verapamil and its metabolites was evaluated in various biological matrices, such as cell cultures and urine. The experimental set-up with the developed method enabled the direct injection of biological samples for the selective isolation, preconcentration, identification and analysis of verapamil and its phase I metabolites by LC-MS(n). This multidimensional approach provided much qualitative information about the metabolic profile of verapamil in various biological matrices. An analytical method was developed for the quantification of verapamil and gallopamil in urine, plasma and cell culture. Acceptable linearity (R(2)=0.9996, 0.9982 and 0.9762) with an average injection repeatability (n=3) of 10, 25 and 15% R.S.D. was determined for urine, plasma and cell culture, respectively. This is the first application of the procedure for the selective metabolic screening of verapamil in biological samples.

Design of chiral LC separations for calcium antagonists on alpha 1-acid glycoprotein and ovomucoid columns.

Three chiral calcium antagonist drugs, gallopamil and two dihydropyridine derivatives, have been successfully separated within short retention times using both the alpha 1-acid glycoprotein chiral stationary phase (Chiral-AGP) and the ovomucoid column (Ultron ES-OVM). Aqueous buffer at defined pH is modified by the addition of an organic component, in order to modulate the retention properties of each system. Optimization of pH and organic modifier is carried out using the modified simplex method, with Kaiser's peak separation function as a criterion. The influence of pH and percentage of organic modifier on retention, selectivity, resolution and column performance are discussed for the two dihydropyridines analysed on Chiral-AGP and Ultron ES-OVM stationary phases. A new method is proposed as a new chiral system suitability test for these protein-based phases, utilizing a racemic mixture of closely eluting verapamil enantiomers as a probe.

Direct determination of the enantiomeric ratio of verapamil, its major metabolite norverapamil and gallopamil in plasma by chiral high-performance liquid chromatography.

Two methods for the determination of the enantiomeric ratio of verapamil in plasma by high-performance liquid chromatography have been developed. On an alpha 1-acid glycoprotein chiral stationary phase (Chiral-AGP) verapamil was separated after the acetylation of the main metabolite norverapamil, which interferes with the resolution of verapamil. On an amylose tris-3,5-dimethylphenylcarbamate column (Chiralpak AD) verapamil and norverapamil were determined simultaneously without prior derivatization. Gallopamil was separated on both columns under similar conditions.

Interspecies differences in the effect of pH on gallopamil protein binding to albumin and alpha 1-acid glycoprotein.

There is little information about the factors which influence drug protein binding between species. We have therefore investigated the role of pH on the binding of gallopamil, a calcium channel antagonist known to exhibit pH-sensitive binding, among four species, human, baboon, bovine, and canine. We used pure protein solutions of alpha 1 acid glycoprotein (AAG) (60 mg.l-1), albumin (45 gm.l-1), and their combination and three values of pH, 7.0, 7.4, and 8.0. Gallopamil protein binding was determined over a concentration range of 2.0 x 10(-7) mol.l-1 to 2.1 x 10(-3) mol.l-1 using equilibrium dialysis. Gallopamil binding in all solutions was best described using a two binding site model in the combination solution and a one binding site model in the pure solutions. pH did not affect the number of identical binding sites. However, the influence of pH on gallopamil binding was species specific. Increasing the pH from 7.0 to 8.0 influenced binding affinity differently between species. There were directionally similar changes in unbound fraction at a gallopamil concentration of 2 x 10(-7) mol.l-1 as pH increased, although there were species differences in the degree of change. In protein solutions containing both AAG and albumin a reduction in pH from 7.4 to 7.0 resulted in species-specific increases in the unbound fraction. Increasing the pH from 7.4 to 8.0 again resulted in species-specific reductions in the unbound fraction of gallopamil. Similar changes were seen when pure AAG or albumin solutions were used, indicating species variance in both gallopamil protein binding and the effect of pH on binding.