Correlation of fluphenazine plasma levels versus clinical response in patients: a pilot study

Plasma levels of fluphenazine in patients receiving fluphenazine decanoate. Relationship to clinical response

The levels of fluphenazine and fluphenazine sulphoxide in schizophrenic patients who were randomly assigned to receive either 5 mg or 25 mg of fluphenazine decanoate every two weeks were monitored. Patients treated with 25 mg of fluphenazine decanoate required three months to reach a steady-state plasma level, indicating that those patients who are being converted from oral to depot fluphenazine should continue to receive oral supplementation during the first three months of treatment with fluphenazine decanoate. Plasma levels of fluphenazine sulphoxide were lower than levels of fluphenazine. At six and nine months following randomisation, there was a statistically significant relationship between lower fluphenazine plasma levels and an increased risk of psychotic exacerbations. A relatively weak relationship was found between fluphenazine plasma levels and akinesia, but non-significant relationships between fluphenazine levels and other neurological side-effects including akathisia, retardation, and tardive dyskinesia. Monitoring the plasma levels may be helpful to clinicians who are attempting to treat stabilised patients with the lowest effective dose of fluphenazine decanoate.

Comparative bioavailability of two tablet formulations of fluphenazine dihydrochloride in drug-free psychiatric patients

The comparative bioavailability of a new tablet formulation of fluphenazine dihydrochloride (5 mg) and a reference product (fluphenazine dihydrochloride, Prolixin, 5 mg) was assessed in drug-free psychiatric patients. Twenty-six patients were initially entered in the study, of whom 22 completed the protocol. Each patient received the test (T) and the reference formulation (R) in a balanced two-way crossover design. Plasma concentrations of fluphenazine were monitored over a period of 48 h after drug administration using a sensitive HPLC method. One patient did not show any measurable plasma concentration for one formulation at any sampling time and, therefore, bioavailability was assessed in the remaining 21 patients. All pharmacokinetic parameters showed wide intersubject variation. The maximum plasma concentration (Cmax), time to Cmax, and area under the curve up to the last measurable concentration (AUClast0), infinity (AUCinfinity0), or truncated areas (such as AUC16(0), AUC24(0) were compared by analyses of variance and found not to be significantly different in each case across the formulations. Except for AUC24(0), AUC32(0), and AUC48(0), ANOVA of all other parameters showed a high power (greater than 80%) to detect a 20% difference in the mean value of each bioequivalence parameter between T and R. The two formulations were found to be bioequivalent in that confidence intervals of the mean values of AUCinfinity0, AUClast0, truncated AUCs, or Cmax for T:R ratios were, in each case, well within the acceptable range of 100 +/- 20%.

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 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.

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)

Clinical pharmacokinetics of the depot antipsychotics

The clinical pharmacokinetics of the 4 depot antipsychotics for which plasma level studies are available (i.e. fluphenazine enanthate and decanoate, haloperidol decanoate, clopenthixol decanoate and flupenthixol decanoate) are reviewed. The proper study of these agents has been handicapped until recently by the necessity of accurately measuring subnanomolar concentrations in plasma. Their kinetic properties, the relationship of plasma concentrations to clinical effects, and conversion from oral to injectable therapy are discussed. The depot antipsychotics are synthesised by esterification of the active drug to a long chain fatty acid and the resultant compound is then dissolved in a vegetable oil. The absorption rate constant is slower than the elimination rate constant and therefore, the depot antipsychotics exhibit 'flip-flop' kinetics where the time to steady-state is a function of the absorption rate, and the concentration at steady-state is a function of the elimination rate. Fluphenazine is available as both an enanthate and decanoate ester (both dissolved in sesame oil), although the decanoate is more commonly used clinically. The enanthate produces peak plasma concentrations on days 2 to 3 and declines with an apparent elimination half-life (i.e. the half-time of the apparent first-order decline of plasma concentrations) of 3.5 to 4 days after a single injection. The decanoate produces an early high peak which occurs during the first day and then declines with an apparent half-life ranging from 6.8 to 9.6 days following a single injection. After multiple injections of fluphenazine decanoate, however, the mean apparent half-life increases to 14.3 days, and the time to reach steady-state is 4 to 6 weeks. Withdrawal studies with fluphenazine decanoate suggest that relapsing patients have a more rapid plasma concentration decline than non-relapsing patients, and that the plasma concentrations do not decline smoothly but may exhibit 'lumps' due to residual release from previous injection sites or multicompartment redistribution. Cigarette smoking has been found to be associated with a 2.33-fold increase in the clearance of fluphenazine decanoate. In 3 different studies, fluphenazine has been proposed to have a therapeutic range from less than 0.15 to 0.5 ng/ml with an upper therapeutic range of 4.0 ng/ml. Plasma concentrations following the decanoate injection are generally lower than, but clinically equivalent to, those attained with the oral form of the drug. Haloperidol decanoate plasma concentrations peak on the seventh day following injection although, in some patients, this peak may occur on the first day.(ABSTRACT TRUNCATED AT 400 WORDS)