Development of radioimmunoassays for trifluoperazine and their application to metabolic studies of the drug

A highly sensitive and specific radioimmunoassay for quantitation of plasma fluphenazine

Antisera of high sensitivity and selectivity were obtained from rabbits immunized with conjugates of hemisuccinylated fluphenazine and porcine thyroglobulin. The antiserum selected (titer 1:6000) for the development of the RIA was obtained after a priming dose and a single iv booster injection three months later. This antiserum had negligible crossreactivity with known available metabolites of fluphenazine (FPZ) and an affinity constant of 2 X 10(10) L/mol. Tritiated FPZ was further purified by HPLC and used as a ligand. The method detects as little as 20 pg/mL of plasma (4 pg/RIA tube) after 1 mL of plasma is extracted. The extraction was performed at a basic pH with heptane: isoamyl alcohol (99:1); the solvent was then back extracted using an acetic phosphate buffer. Recoveries were uniformly high (88.6 +/- 2.1%), and this aqueous buffer extract was used directly in the RIA procedure. The assay has intra- and interassay coefficients of variation of 5.8 and 8.2%, respectively, in a plasma concentration of 95 pg/mL. Results using this procedure have been cross validated against an HPLC procedure (r = 0.952, slope = 1.032, intercept = 0.009, n = 18). In a single-dose FPZ study (10 mg, po), plasma FPZ levels in 25 normal volunteers could be monitored greater than 48 h post dose. Single plasma level profiles, after an initial injection of 12.5 mg of FPZ decanoate, could be measured greater than 36 d, and, in some cases, up to 100 d post dose.

Radioimmunoassay for the 7-hydroxy metabolite of trifluoperazine and its application to a kinetic study in human volunteers

A hapten derivative of the 7-hydroxy metabolite of trifluoperazine, 7-hydroxy-10-[[3-[4-(2-carboxyethyl)-1-piperazinyl]propyl]]-2 -tri-fluromethyl-10H-phenothiazine, was synthesized and coupled to bovine serum albumin. Immunization of New Zealand white rabbits with this drug-protein conjugate resulted in the production of antisera, one of which was subsequently utilized in the development of an RIA procedure. The described RIA for the first time enables the quantitation of the 7-hydroxy metabolite of trifluoperazine in human plasma after oral administration of single and therapeutic doses of trifluoperazine, in which 20 pg of the nonconjugated 7-hydroxy metabolite in 200 microL of plasma can be measured with a CV of less than 3% in B/Bo readings. Similar results were obtained by this assay procedure with or without the selective extraction of the 7-hydroxy metabolite and in the presence or absence of a large excess of trifluoperazine and other suspected major metabolites, such as the sulfoxide and N4'-oxide metabolites. This RIA procedure, together with a previously developed RIA for trifluoperazine, was used to directly determine plasma concentrations of trifluoperazine and its 7-hydroxy metabolite after administration of a single 5-mg oral dose of trifluoperazine to six healthy male volunteers. The mean +/- SD for the peak concentration (Cmax), the time to Cmax, the area under the curve from 0 to 24 h and, the apparent terminal elimination half-life for the 7-hydroxy metabolite were found to be 0.86 +/- 0.2 ng/mL, 6.2 +/- 1.6 h, 11.1 +/- 4.9 ng . h/mL, and 10.6 +/- 5.7 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioimmunoassay for the sulfoxide metabolite of trifluoperazine and its application to a kinetic study in humans

Antibodies were produced in rabbits immunized with 10-[[3-[4-(2-carboxyethyl)-1-piperazinyl]-propyl]]-2 -trifluoromethyl-10H-phenothiazine sulfoxide-bovine serum albumin conjugate. The subsequently developed radioimmunoassay (RIA) procedure enables, for the first time, the quantitation of the sulfoxide metabolite of trifluoperazine in the plasma of humans after administration of therapeutic doses of trifluoperazine, in which 60 pg of the sulfoxide metabolite in 200 microL of plasma can be measured with a CV of less than 3%. Similar results were obtained by this assay with or without a benzene extraction step and also in the presence or absence of a large excess of trifluoperazine and suspected major metabolites of trifluoperazine. This RIA procedure, together with a previously developed RIA for trifluoperazine was used to directly determine plasma concentrations of trifluoperazine and its sulfoxide metabolite after administration of a single, low, oral dose of trifluoperazine to five healthy volunteers. The rapidly appearing, relatively high concentrations of the sulfoxide metabolite are indicative of presystemic sulfoxidation. The mean plasma elimination half-life for the sulfoxide metabolic of trifluoperazine was 5.8 +/- 1.3 h.

Radioimmunoassay for psychotropic drugs. III: Synthesis and properties of haptens for trifluoperazine and fluphenazine

For the development of radioimmunoassay procedures for trifluoperazine and fluphenazine, three haptens, N-(2-carboxyethyl)desmethyltrifluoperazine, N-(4-carboxybutyl)desmethyltrifluoperazine, and 10-[3-(4-carboxyethylpiperazinyl)-3-oxopropyl]-2-trifluoromethyl-+ ++10H- phenothiazine, were synthesized and characterized. Each hapten was coupled to bovine serum albumin, and the number of hapten residues per mole of bovine serum albumin was calculated by UV spectrophotometric methods. Antibodies to each hapten-protein conjugate were developed in rabbits, and titers of the antisera were checked by evaluating their binding characteristics to the tritiated drug.

Radioimmunoassays for phenothiazine drugs and their major metabolites in plasma

Radioimmunoassay procedures have been developed for some phenothiazine drugs and their major metabolites which are capable of quantitating 0.3 ng/ml or less in a 200 microliter plasma sample with a coefficient of variation less than 3%. They were developed with a view to their use in pilot investigations of plasma level versus clinical response correlations. The development of the procedures for trifluoperazine are described in this workshop. Antisera to trifluoperazine have been raised in New Zealand white rabbits to several different types of immunogens, where there was variation in the length and nature of the N-10 side chain attached to the phenothiazine nucleus, as well as in the number of hapten residues coupled to bovine serum albumin. An improved radioimmunoassay for trifluoperazine has been developed which showed cross-reactivities to the N-desmethyl and 7-hydroxy metabolites of trifluoperazine of the order of 12 and 11%, respectively, in comparison to the 26 and 24% cross-reactivity, respectively, for the same metabolites by a previously reported procedure.