Measurement of plasma and erythrocyte chlorpromazine and N-monodesmethylchlorpromazine levels by gas chromatography with a nitrogen sensitive detector.

A new gas chromatographic method, employing a nitrogenphorphorus sensitive detector, for the measurement of chlorpromazine and N-monodesmethylchlorpromazine is described. The application of the method to the measurement of the drugs in clinical plasma and erythrocyte samples is demonstrated. It was found that the chlorpromazine concentration in the erythrocytes is positively and linearly correlated with the drug level in the plasma. However, a 4-fold inter-individual variation in the erythrocyte/plasma concentration ratios was evident. The concentration of the metabolite in the erythrocytes was found to be up to 27% of that of the parent compound. Chlorpromazine was unstable in plasma but stable in erythrocytes during a week's storage in the dark at -20°. The possible clinical implications of our findings are discussed.