Plasma levels and half lives of thioridazine and some of its metabolites. II. Low doses in older psychiatric patients.

Plasma-levels of thioridazine, mesoridazine, sulphoridazine and two other metabolites were determined in ten older chronic psychotic patients on thioridazine therapy. The plasma-level before the morning dose of thioridazine was the most reliable parameter for clinical studies. An intra-individual relationship between lower doses of thioridazine and plasma-levels was found. The percentage contribution of psychoactive compounds to the total sum of "thioridazine plus metabolites" ranged from 43-74%. The mean "early disappearance half-life" of thioridazine was 5 hours, and its mean "late disappearance half-life" was 26 hours.