Fluphenazine determination in human plasma by a sensitive gas chromatographic method using nitrogen detector.

This report describes a sensitive gas chromatographic method with the use of a nitrogen detector for the determination of fluphenazine at therapeutic concentrations in human plasma. Fluphenazine was measured as its acetyl derivative. Perphenazine, a structurally similar phenothiazine, was used as an internal standard. The acetylated derivatives were identified by GC/MS. Within-day coefficient of variation of the method over the concentration range 0.5 to 10 ng/ml fluphenazine was 6.7%. Fluphenazine concentrations in the plasma of patients receiving the drug orally (as dihydrochloride) or intramuscularly (as decanoate) were measured. There were large interindividual variations both in plasma levels and half-lives of fluphenazine in different patients treated with the same doses.