The authors monitored serum levels of fluphenazine in nine patients
following injections of fluphenazine decanoate ranging from 10 to 75 mg.
Levels were detected by a radioreceptor assay based on the ability of the
drug to complete with 3H-spiroperidol for binding to dopamine receptors in
rat caudate membranes. Serum levels of fluphenazine were quite stable over
a 2- to 3-week period following single intramuscular injections of the
decanoate and correlated with injected dose. Following decanoate treatment
serum levels of fluphenazine are substantially lower than levels observed
for most other neuroleptics administered orally. This raises questions as
to how fluphenazine decanoate can exert therapeutic actions.