A pilot of plasma thioridazine and metabolites in chronically treated patients.

Plasma concentrations of thioridazine, mesoridazine, sulphoridazine and thioridazine ring sulphoxide have been measured individually by specific gas-liquid chromatographic (GLC) methods, and collectively by a radio-receptor assay, in 16 elderly in-patients during chronic treatment. The sulphoridazine level was above 0.135 microgram/ml in 5 out of 6 symptomatically well-controlled patients, and below this level in 9 out of 10 who were poorly controlled. No such division was so clear for the other substances measured. A new assay for the total dopamine receptor-blocking activity of the plasma correlated highly at lower levels with the sum of drug plus metabolites obtained by GLC, but exceeded the sum at higher values. Both sulphoridazine and neuroleptic levels need further study.