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Vol. 305, Issue 2, 625-631, May 2003
Centre for Addiction and Mental Health, Toronto, Ontario, Canada
(S.K., S.C.V., B.A.B., J.N.N.); Department of Psychiatry, University of
Toronto, Toronto, Ontario, Canada (S.K., J.N.N.)
What is the appropriate dose of an antipsychotic in an animal model?
The literature reveals no standard rationale across studies. This study
was designed to use in vivo dopamine D2 receptor occupancy as a cross-species principle for deriving clinically comparable doses
for animal models. The relationship between dose, plasma levels, and in
vivo dopamine D2 receptor occupancy was established in rats
for a range of doses administered as a single dose or multiple doses
(daily injections or osmotic minipump infusions) for five of the most
commonly used antipsychotics. As a single dose, haloperidol (0.04-0.08
mg/kg), clozapine (5-15 mg/kg), olanzapine (1-2 mg/kg), risperidone
(0.5-1 mg/kg), and quetiapine (10-25 mg/kg) reached clinically
comparable occupancies. However, when these "optimal" single doses
were administered as multiple doses, either by injection or by a
mini-pump, it led to no or inappropriately low trough (24-h)
occupancies. This discrepancy arises because the half-life of
antipsychotics in rodents is 4 to 6 times faster than in humans. Only
when doses 5 times higher than the optimal single dose were
administered by pump were clinically comparable occupancies obtained
(e.g., haloperidol, 0.25 mg/kg/day; olanzapine, 7.5 mg/kg/day). This
could not be achieved for clozapine or quetiapine due to solubility and
administration constraints. The study provides a rationale as well as
clinically comparable dosing regimens for animal studies and raises
questions about the inferences drawn from previous studies that have
used doses unrepresentative of the clinical situation.
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