Rapid HPLC assay for verapamil and its metabolites: use for application to in vitro studies.

An improved method using isocratic reversed phase HPLC is presented for the extraction and rapid determination of verapamil and its main metabolites in microsomal preparations and cell culture media. Possibilities for using the method to estimate cytochrome P450 enzymes in microsomal test systems and hepatocyte cultures are described. The studies show that primary hepatocyte cultures are suitable for studying the metabolism and interactions of pharmaceuticals in vitro and could be superior to microsomal systems in many cases.