Plasma levels of fluphenazine and prolactin in psychiatric patients.

A total of 100 patients receiving fluphenazine (FPZ) decanoate for at least 12 months (96 schizophrenics and 4 other diagnoses) were investigated for plasma levels of FPZ and prolactin on the day of injection (day 0) and 7 days later (day 7). The plasma FPZ level significantly correlated with the weekly dose of FPZ. The plasma FPZ level per weekly FPZ dose multiplied by 100 (the FPZ ratio) showed a 20-fold variation. The FPZ ratio was significantly higher in the day- and in-patients (hospital-patients) than in out-patients. The plasma prolactin level significantly correlated with the plasma FPZ level but the prolactin to FPZ ratio negatively correlated with the plasma FPZ level. The prolactin to FPZ ratio was lower in the hospital patients than in the out-patients. This may suggest either that the high prolactin to FPZ ratio is an indicator of the therapeutic efficacy of FPZ or that there are at least two biologically distinct subgroups, one with a sharp prolactin response to FPZ, therefore with good prognosis, and another with the reverse direction.