MONITORING PLASMA-LEVELS OF FLUPHENAZINE DURING CHRONIC THERAPY WITH FLUPHENAZINE DECANOATE

This study was conducted to examine the interpatient variability in st eady-state plasma concentrations of fluphenazine by repeat depot intra muscular administration, and to determine the relationship between the se concentrations and clinical state. Steady-state pre-dose concentrat ions of fluphenazine in plasma were measured using a sensitive and spe cific gas chromatography/mass spectrometry (GC/MS) assay in 24 patient s with schizophrenia who were receiving continuous treatment with depo t intramuscular fluphenazine decanoate. Clinical response was measured using the Andreasen Scale for positive and negative symptoms, Steady- state plasma concentrations of fluphenazine ranged from undetectable ( <0.1 ng/ml) to 27.9 ng/ml, with a median of 0.5 ng/ml. No significant associations were found between plasma concentration and dosage, or ag e and sex of the patient. Steady-state plasma concentrations in patien ts taking anticholinergic agents were significantly higher than in pat ients not receiving such drugs (P<0.05 by Mann-Whitney U-test). Poorer control, expressed as the sum of the negative symptom scores or the s um of the positive and negative symptom scores, was related to higher log transformed plasma concentrations of fluphenazine and higher fluph enazine decanoate dosage. The log transformed plasma concentrations of fluphenazine and the fluphenazine decanoate dosages were weakly relat ed. Patients receiving another antipsychotic drug in addition to fluph enazine decanoate tended to have poorer clinical control and higher do sages of fluphenazine decanoate. These results indicate the useful rol e that plasma level monitoring can fulfil in identifying patients who are therapy-resistant despite high plasma levels.