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Preliminary Findings

Svante Nyberg, MD, PhD; Lars Farde, MD, PhD; Christer Halldin, PhD

Arch Gen Psychiatry. 1997;54(10):953-958.

Abstract
Background
Antipsychotic drugs in depot formulations may prevent psychotic relapses, even after complete withdrawal. To examine the duration of drug remaining in the brain, central D₂ dopamine receptor occupancy was measured with positron emission tomography for a year after discontinuation of depot neuroleptic treatment.

Methods
Four schizophrenic patients were withdrawn from low-dose treatment with haloperidol decanoate (30-50 mg every 4 weeks). They were examined repeatedly with positron emission tomography and the radioligand carbon 11-labeled raclopride during the following year. At end point, a Scatchard analysis was performed to determine the density and affinity of D₂ dopamine receptors.

Results
Occupancy of D₂ dopamine receptors was highest 1 week after depot injection (66%, 77%, 82%, and 78% in 4 patients) and then decreased slowly. Six months after discontinuation of treatment, D₂ dopamine receptor occupancy was 24%, 32%, and 34% in 3 patients. After 1 year, D₂ dopamine receptor density and affinity in 2 patients were within the ranges of control subjects, suggesting no remaining haloperidol.

Conclusions
Our preliminary finding of persistence of D₂2 dopamine receptor occupancy indicates that commonly used doses of haloperidol decanoate (200 mg every 4 weeks) maintain antipsychotic levels of receptor occupancy even 16 weeks after discontinuation of treatment. This may explain the lower relapse rates in patients withdrawn from depot neuroleptic treatment compared with those with-drawn from oral treatment. In addition, the remaining occupancy may confound the clinical evaluation of subsequent treatments. For controlled clinical trials of new antipsychotic drugs, we suggest a minimum washout of 6 months after the last depot injection.

Author Affiliations
From the Psychiatry Section, Department of Clinical Neuroscience, Karolinska Institutet, Karolinska Hospital, Stockholm, Sweden.

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