Radioimmunoassay for a new phenothiazine derivative and its application.

Fluphenazine-4-chlorophenoxy-isobutyrate ester, a new phenothiazine derivative was synthesized in the Institute for Drug Research Budapest. Radioimmunoassay was developed for the therapeutic monitoring of the drug level after intramuscular depot injection. The fluphenazine hapten was coupled to BSA by mixed-anhydride method. Antisera were produced to this conjugation in New-Zealand white rabbits and were tested for the antibody-titer. The specificity was tested by the cross-reaction with phenothiazine-analogues and other psychotropics. Strong cross-reaction was found with compounds possessing piperazine in side chain (trifluoperazine, perphenazine), but other psychotropic drugs did not react. Tritium-labelled trifluoperazine (spec. activity: 3.5 TBq/mmol) was used as a tracer in the radioimmunoassay. The detection limit was 75 pg with a CV of < 5% in 50 microliters plasma sample (equivalent to 1.5 ng/ml concentration) and a standard curve in the 3 ng/ml-50 ng/ml GYKI-22441 concentration range showed a CV of < 10%. Preliminary pharmacokinetic study was performed in Beagle dogs after intramuscular depot injection with GYKI-22441 in sesame oil in a dose of 0.1 mg/kg. The GYKI-22441 concentration of the plasma samples were measured by the RIA method during a 28-day interval after the treatment and was evaluated by the MultiCalc Immunoassay Data Management program (Pharmacia).