Adverse effects associated with conventional antipsychotic medications can interfere with function, reduce the quality of life, promote poor compliance and compromise drug therapy. Long-acting injectable medication is especially successful in schizophrenic patients who forget to take medication or skip oral doses. It is not as successful in patients who decline antipsychotic medication because of unpleasant side effects. Carpenter and associates tested a new dose reduction approach that increased the interval between injections during intramuscular antipsychotic therapy.

Fifty outpatients with schizophrenia or schizoaffective disorder were randomly assigned to receive 25 mg of fluphenazine decanoate intramuscularly every two weeks or every six weeks for 54 weeks. Thirty-three patients completed the one-year, double-blind study.

The number of patients who met the criteria for treatment failure were similar in the group that was given the drug every two weeks and in the group that was given the drug every six weeks. Two patients were hospitalized, both from the group receiving the drug every two weeks. Relapse durations were comparable for the patients in both groups who completed the study. The goal of cumulative fluphenazine dose reduction was met with the six-week regimen. The mean cumulative dose of fluphenazine over the one-year period was 725 mg for the two-week group and 439 mg for the six-week group.

Both treatment groups had low levels of extrapyramidal and dyskinetic symptoms at baseline and throughout the study period. Extrapyramidal symptoms and dyskinesia scores were similar for both groups at six months and at one year. Psychosocial functioning and symptom outcomes were comparable for the two treatment groups, reflecting mild to moderate impairment for the duration of the study.

No differences were apparent between the two fluphenazine decanoate regimens in treatment efficacy or effectiveness. The patients who were given the drug every six weeks achieved a significant decrease in cumulative antipsychotic dose without a symptomatic disadvantage. No differences were apparent in adverse drug effects or functioning measures that might have favored the lower dose because of decreased antipsychotic drug exposure.

The authors conclude that the study's failure to find a significant advantage in administering the drug every two weeks suggests that standard practice often results in patients receiving more maintenance medication than is required to prevent relapse. Long-acting, injectable antipsychotic medication has substantial advantages for many schizophrenic patients and is underused.