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

Human moricizine metabolism. I. Isolation and identification of metabolites in human urine

1. Using synthetic standards and/or spectral data, seven moricizine metabolites were structurally identified in human urine. Two novel metabolites were identified as phenothiazine-2-carbamic acid and ethyl [10-(3-aminopropionyl) phenothiazin-2-yl] carbamate. Two novel human moricizine metabolites, 2-amino-10-(3-morpholino-propionyl) phenothiazine, a previously identified dog metabolite, and 2-aminophenothiazine, a previously identified rat metabolite, were also identified. Three additional human metabolites, phenothiazine-2-carbamic acid ethyl ester sulphoxide (P2CAEES), moricizine sulphoxide, and ethyl ¿10-[N-(2'-hydroxyethyl)3-aminopropionyl] phenothiazin-2-yl¿ carbamate, all previously described in the literature, were observed. 2. Both 2-amino-10-(3-morpholinopropionyl) phenothiazine and ethyl [10-(3-aminopropionyl) phenothiazin-2-yl] carbamate, and possibly ethyl ¿10-[N-(2'-hydroxyethyl) 3-aminopropionyl]phenothiazin-2-yl¿ carbamate, possess the structural characteristics thought to be necessary for class 1 antiarrhythmic activity.

Structural changes by sulfoxidation of phenothiazine drugs

The side-chain conformations of psychoactive phenothiazine drugs in crystals are different from those of biologically inactive ring sulfoxide metabolites. This study examines the potential energies, molecular conformations and electrostatic potentials in chlorpromazine, levomepromazine (methotrimeprazine), their sulfoxide metabolites and methoxypromazine. The purpose of the study was to examine the significance of the different crystal conformations of active and inactive phenothiazine derivatives, and to determine why phenothiazine drugs lose most of their biological activity by sulfoxidation. Quantum mechanics and molecular mechanics calculations demonstrated that conformations with the side chain folded over the ring structure had lowest potential energy in vacuo, both in the drugs and in the sulfoxide metabolites. In the sulfoxides, side chain conformations corresponding to the crystal structure of chlorpromazine sulfoxide were characterized by stronger negative electrostatic potentials around the ring system than in the parent drugs. This may weaken the electrostatic interaction of sulfoxide metabolites with negatively charged domains in dopamine receptors, and cause the sulfoxides to be virtually inactive in dopamine receptor binding and related pharmacological tests.

Radioimmunoassay for fluphenazine sulfoxide in human plasma

Antisera to fluphenazine sulfoxide were raised in New Zealand white rabbits to an immunogen synthesized by covalent linkage of bovine serum albumin to 10-[[3-[4-(4-carboxybutyl)-1-piperazinyl] propyl]]-2-trifluoromethyl-10H-phenothiazine 5-sulfoxide. With use of an antiserum, a radioimmunoassay for fluphenazine sulfoxide was developed that is able to quantitate 0.156 ng ml-1 using only a 200 microliter plasma sample with a coefficient of variation less than 5%. The antiserum had negligible cross-reactivities to fluphenazine (less than 1%) and its important metabolites, such as fluphenazine N4'-oxide (1%), 7-hydroxyfluphenazine (less than 1%), and N4'-deshydroxy-ethylfluphenazine (1%). The cross-reactivities with structurally similar phenothiazine 5-sulfoxides, such as those of trifluoperazine, prochlorperazine, perphenazine, and N4'-deshydroxyethylfluphenazine, were considerable, such that the antiserum can be used to develop a quantitative radioimmunoassay for any of these compounds. The reported radioimmunoassay was found to be suitable and adequate to quantitate fluphenazine sulfoxide in the plasma of patients treated with oral or intramuscular fluphenazine.

A pharmacokinetic study of trifluoperazine in two ethnic populations

The single dose pharmacokinetics of trifluoperazine (5 mg, Stelazine) were investigated in black (n = 25) and white (n = 32) healthy male subjects. Plasma samples were harvested over 24 h and analysed by a GLC-MS method. There were wide intersubject variations in all pharmacokinetic parameters examined, including Cmax, AUC, apparent oral volume of distribution at steady state, and elimination half-life. For each of these parameters the distribution was positively skewed in both blacks and whites and the geometric mean gave a better estimate of central tendency than the corresponding arithmetic mean. In all pharmacokinetic parameters examined there was no significant difference detected between black and white subjects or between smokers and non-smokers.

Plasma level monitoring of antipsychotic drugs. Clinical utility

The steady-state plasma concentrations of antipsychotic drugs show large interpatient variations but remain relatively stable from day to day in each individual patient. Monitoring of antipsychotic drug concentrations in plasma might be of value provided the patients are treated with only 1 antipsychotic drug. Some studies have reported a relationship between therapeutic response and serum antipsychotic drug 'concentrations' as measured using the radioreceptor assay (RRA) method, which measures dopamine receptor-blocking activity in plasma. Most studies, however, have failed to demonstrate such a relationship, and the RRA does not seem to provide the generally useful tool for plasma concentration monitoring of antipsychotic drugs that was hoped for initially. A lack of correlation between dopamine receptor-blocking activity in plasma and therapeutic response may be due to differences in the blood-brain distribution of both antipsychotic drugs and their active metabolites. Chemical assay methods (e.g. GLC and HPLC) have been used in studies which examined the relationships between therapeutic response and antipsychotic drug concentrations in red blood cells and in plasma. It seems that for these drugs, measuring red blood cell concentrations does not offer any significant advantage over measuring plasma concentrations. Reasonably controlled studies of plasma concentration-response relationships using randomly allocated, fixed dosages of chlorpromazine, fluphenazine, haloperidol, perphenazine, sulpiride, thioridazine and thiothixene have been published but often involve relatively few patients. A correlation between therapeutic response and plasma concentrations of thioridazine and its metabolites has not been demonstrated, and plasma level monitoring of thioridazine and its metabolites therefore appears to have no clinical value. Clinical behavioural deterioration concomitant with high plasma concentrations of chlorpromazine and haloperidol have been reported. A dosage reduction might be considered after 2 to 4 weeks' treatment in non-responders who have plasma chlorpromazine concentrations above 100 to 150 micrograms/L or plasma haloperidol concentrations above 20 to 30 micrograms/L. Non-responders and good responders to chlorpromazine treatment, however, have plasma drug concentrations in the same range, and a therapeutic range of plasma chlorpromazine levels has not been defined. Therapeutic plasma haloperidol concentrations (i.e. 'window') in the range of 5 to 20 micrograms/L have been reported by some investigators, but others have found no such relationship.(ABSTRACT TRUNCATED AT 400 WORDS)

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)