Radioreceptor assay and high-performance liquid chromatography yield similar results for serum thioridazine and its major metabolites.

Thioridazine and its major metabolites were quantified in serum of thioridazine-treated psychiatric patients by radioreceptor assay and high performance liquid chromatography (HPLC) every second day during 3 weeks of drug administration. Serum neuroleptic levels measured by radioreceptor assay and serum concentrations of thioridazine and its active metabolites estimated by HPLC correlated (r = 0.82, n = 60); the intra- and interassay coefficients of variation of both assays were low (less than 7%). Thus, serum thioridazine can be adequately monitored by radioreceptor assay as well as by HPLC.