Electrocardiographic changes and serum concentrations in thioridazine-treated patients.

Electrocardiograms and serum concentrations of thioridazine and its metabolites were studied in 43 patients with paranoid psychosis. Two types of T-wave changes were distinguished: Type I with rounded, leveled, or notched T-waves, and Types II with diphasic waves. Significant positive correlations were found between serum drug concentrations and the Type I changes, while the Type II changes showed no concentration dependence. The two types of T-wave changes also differed in respect of prevalence, time of onset, duration, and variation with sex. The ECG response to thioridazine provides useful information about the serum drug concentrations.