Persistence of fluphenazine in plasma after decanoate withdrawal

We discontinued fluphenazine decanoate using a double-blind, crossover random order design, in 12 recent onset clinically stable schizophrenics who had been given fluphenazine decanoate 12.5 mg intramuscularly every 2 weeks for at least 1 year prior to drug withdrawal. Each condition (drug or placebo) lasted 12 weeks. Using a radioimmunoassay verified by comparison to a gas chromatographic-mass spectrometric method, plasma fluphenazine levels were measured every 2 weeks during drug continuation and drug withdrawal conditions. No patient relapsed over the 24-week period of the study. Mean fluphenazine levels between drug continuation and withdrawal conditions showed a progressively larger difference over time, although significant differences were not seen until week 8. By week 12 after drug withdrawal, 33% of subjects still showed notable plasma fluphenazine levels. On the basis of our preliminary findings, we suggest that 2-week intervals between injections may be too short and that wider intervals may achieve similar clinical results.