Antibodies have been produced in rabbits immunized with a fluphenazine succinate-human serum albumin conjugate. By radioimmunoassay it is possible to quantify fluphenazine (FPZ), related phenothiazine drugs and several of their metabolites at the femtomole level. As little as 370 fmol (160 pg) of FPZ can be detected and up to 0.4 ml of plasma can be added to the incubation mixture (final volume = 1.1 ml). The phenothiazine heterocyclic nucleus is immunodominant and determines the specificity of the antiserum. When a parent drug cross-reacts significantly with antibody, its 7-hydroxide, N-oxide and N-10 side chain altered metabolites can also be determined by the assay. The 8-hydroxide, sulfoxide and 7-hydroxyglucuronide metabolites are not detectable unless present in large amounts. High-performance liquid chromatography was used to separate phenothiazine drugs and metabolites. Since the antiserum has broad specificity, a combined high-performance liquid chromatography and radioimmunoassay procedure permits the identification and quantification of a phenothiazine drug and its serologically reactive metabolites. Patterns of high-performance liquid chromatographic elution and extent of immunologic cross-reaction are characteristic for metabolites relative to the parent drug. This procedure offers distinct advantages in the analysis of this complex family of compounds. FPZ was quantitatively extracted from plasma samples obtained from patients receiving FPZ per os. Although large amounts of serological activity were present in the samples 2 to 6 hr after FPZ ingestion, only 2 to 23% was extractable. The major contributors to the serological activity at times greater than 6 hr were FPZ metabolites. In a preliminary application of the combined techniques, FPZ and a metabolite identified as N-[alpha-(trifluoromethylphenothiazinyl-10)propyl]perazine were quantified in the organic extract of one plasma sample
