A depot neuroleptic withdrawal study. Plasma concentration of fluphenazine and flupenthixol and relapse frequency.

A double-blind withdrawal trial in 41 chronic schizophrenic outpatients was carried out during 6 months. Depot neuroleptics (fluphenazine decanoate or flupenthixol decanoate) were compared with placebo to evaluate clinical and neurological effects during continued therapy and during withdrawal. The drugs were significantly more effective than placebo in preventing relapse and rehospitalization. In the placebo group 62% relapsed compared to 27% in the drug group. There was a weak and nonsignificant tendency to a higher relapse frequency in the flupenthixol group compared to the fluphenazine group. After withdrawal for 6 months, plasma levels for fluphenazine were detectable. Plasma levels for flupenthixol were not detectable after 9 weeks of withdrawal. The differences in the plasma levels may possibly explain the difference in relapse rate between the two depot neuroleptics. Furthermore, it was found that the patients who relapsed during fluphenazine treatment had a significantly lower plasma level of the drug than patients who did not relapse during treatment. The results from this study provide some information on the therapeutic levels of fluphenazine and flupenthixol in schizophrenic patients.