Monthly Administration of Long-Acting Injectable Risperidone and Striatal Dopamine D<sub>2</sub> Receptor Occupancy for the Management of Schizophrenia
J Clin Psychiatry 2008;69(8):1281-1286
© Copyright 2015 Physicians Postgraduate Press, Inc.
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Objective: Long-acting risperidone
administered intramuscularly biweekly is approved for
the management of schizophrenia. However, dosing
of long-acting antipsychotics is frequently extended
in clinical practice, and a recent clinical trial has
lent support to monthly dosing of long-acting
risperidone. The objective of this positron
emission tomography (PET) study was to examine the
striatal dopamine D2 binding of long-acting
risperidone administered intramuscularly once a month.
Method: Following at least 3
maintenance monthly injections of 50 mg long-acting
risperidone, 7 patients with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder
underwent PET using [11C]raclopride to measure
D2 binding potential within 4 days of the next
scheduled injection. Data were collected from May
to October 2003. This PET study was part of a
larger 52-week clinical study wherein individuals
received long-acting risperidone once monthly over
a 1-year interval. One-year follow-up data were obtained from the 52-week parent investigation.
Results: The mean ± SD
D2 receptor occupancy was 56% ± 24% (range, 29%-82%). Of note,
there were 4 subjects with less than 60%
D2 occupancy, none of whom relapsed over the course of the
1-year follow-up. The mean ± SD total plasma
level of risperidone plus 9-hydroxyrisperidone was
16.6 ± 12.3 ng/mL (range, 5.7-40.8).
Conclusion: As with plasma levels, there
was considerable variability in D2 occupancy levels
for individuals receiving long-acting risperidone.
This work suggests a possibility that sustained
D2 occupancy at or above the accepted threshold with
acute clinical response may not be necessary to
maintain response, a hypothesis with important clinical
implications as we consider antipsychotic dosing
and future antipsychotic development.
Trial Registration: clinicaltrials.gov