Red blood cell and plasma levels of thioridazine and mesoridazine in schizophrenic patients.

Thioridazine and mesoridazine levels and levels of thioridazine plus metabolites were determined in plasma and red blood cells (RBC) by gas-liquid chromatography (GLC) and spectrofluorometry (SP), respectively, in schizophrenic patients treated with fixed doses of thioridazine. There was wide interpatient variability in RBC:plasma ratios for thioridazine and mesoridazine, a higher ratio of thioridazine to mesoridazine in RBC than plasma, and a higher ratio of GLC total (thioridazine plus mesoridazine), to SP-determined total drug constituents in RBC than in plasma. RBC showed a monotonic increase in drug levels with dose, whereas levels of drug in the plasma began to level off above the 250 mg/day dose. Drug levels 24 h after the acute dose did not predict steady-state blood levels in plasma or RBC.