Brain and plasma pharmacokinetics of aripiprazole in patients with schizophrenia: An [F-18]fallypride PET study
ABSTRACT Aripiprazole at clinically effective doses occupies some 90% of striatal dopamine 2 and 3 (D(2)/D(3)) receptors. In order to further characterize its extrastriatal and time-dependent binding characteristics, the authors conducted positron emission tomography (PET) studies with the D(2)/D(3) antagonist [(18)F]fallypride at varying time points after the last aripiprazole administration in patients with schizophrenia.
Sixteen inpatients with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder receiving treatment with aripiprazole underwent an [(18)F]fallypride PET scan. Receptor occupancy was calculated as the percentage reduction in binding potential relative to unblocked values measured in eight age-matched, medication-free patients with schizophrenia. In addition, aripiprazole serum concentrations were determined as part of a routine therapeutic drug monitoring program in a large group of patients (N=128) treated with aripiprazole.
Mean dopamine D(2)/D(3) receptor occupancy was high in all brain regions investigated, with no binding difference across brain regions. Nonlinear regression analysis revealed maximum attainable receptor occupancy (E(max)) values close to saturation. The values for serum concentration predicted to provide 50% of E(max) (EC(50)) were in the range of 5-10 ng/ml in all brain regions. The D(2)/D(3) receptors were completely saturated when serum aripiprazole concentration exceeded 100-150 ng/ml. The mean concentration in the large clinical patient sample was 228 ng/ml (SD=142).
Because of its high affinity for D(2)/D(3) receptors and its long elimination half-life, aripiprazole at clinical doses occupies a high fraction of its target receptor everywhere in the brain. Its dissociation from those receptors is very slow, such that the authors calculate from the results that in patients with serum aripiprazole concentrations in the range typical for clinical practice, D(2)/D(3) receptors must remain nearly saturated for as long as 1 week after the last dose.
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ABSTRACT: Aripiprazole lauroxil is a linker lipid ester of aripiprazole for extended-release intramuscular (IM) injection. This multicenter, randomized, open-label study evaluated the pharmacokinetics (PK), relative bioavailability, and tolerability of a single IM deltoid or gluteal injection of aripiprazole lauroxil in adult subjects with chronic stable schizophrenia or schizoaffective disorder. Forty-six subjects were randomized 1:1 to aripiprazole lauroxil 441mg IM in the deltoid or gluteal muscle. Samples were collected through 89days post-dose to measure levels of aripiprazole lauroxil, N-hydroxymethyl aripiprazole, aripiprazole, and dehydro-aripiprazole. Forty-three (93.5%) subjects completed all study assessments; most were CYP2D6 extensive or immediate metabolizers (96%); two (4%) were poor metabolizers. The PK of aripiprazole following aripiprazole lauroxil was characterized by a steady rise in plasma concentrations (Tmax 44-50days), a broad peak, and prolonged exposure attributable to the dissolution of aripiprazole lauroxil and formation rate-limited elimination of aripiprazole (t1/2=15.4-19.2days). Deltoid vs. gluteal administration resulted in slightly higher Cmax aripiprazole concentrations [1.31 (1.02, 1.67); GMR 90% CI]; total exposure (AUCinf) was similar between sites of administration [0.84 (0.57, 1.24)]. N-hydroxymethyl-aripiprazole and dehydro-aripiprazole exposures were 10% and 33-36%, respectively, of aripiprazole exposure following aripiprazole lauroxil. The most common adverse events were injection site pain in 20 subjects (43.5%) and headache in 6 subjects (13.0%) of mild intensity occurring at a similar rate with deltoid and gluteal administration. Exposure ranges with deltoid and gluteal administration overlapped, suggesting that these sites may be used interchangeably. Despite a higher incidence of adverse events, deltoid muscle provides a more accessible injection site and could facilitate patient acceptance.Schizophrenia Research 09/2014; DOI:10.1016/j.schres.2014.09.021 · 4.43 Impact Factor
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ABSTRACT: We herein examined the biological effects of cells treated with 18F labeled drugs for Positron Emission Tomography (PET). The relationship between the intracellular distribution of 18F and levels of damaged DNA has yet to be clarified in detail. We used culture cells (Chinese Hamster Ovary cells) treated with two types of 18F labeled drugs, fluorodeoxyglucose (FDG) and fluorine ion (HF). FDG efficiently accumulated in cells, whereas HF did not. To examine the induction of DNA double strand breaks (DSB), we measured the number of foci for 53BP1 that formed at the site of DNA DSB. The results revealed that although radioactivity levels were the same, the induction of 53BP1 foci was stronger in cells treated with 18F-FDG than in those treated with 18F-HF. The clonogenic survival of cells was significantly lower with 18F-FDG than with 18F-HF. We concluded that the efficient accumulation of 18F in cells led to stronger biological effects due to more severe cellular lethality via the induction of DNA DSB.Biochemical and Biophysical Research Communications 10/2014; DOI:10.1016/j.bbrc.2014.09.136 · 2.28 Impact Factor
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ABSTRACT: Neuregulin-1 (NRG1) and ErbB4 genes have been identified as candidate genes for schizophrenia. Post-mortem studies indicated that NRG1-ErbB4 signalling is impaired in schizophrenia subjects. This study investigated whether short- or long-term antipsychotic treatment has different effects on the expression of NRG1 and ErbB4 receptors. Female Sprague-Dawley rats were treated orally with either aripiprazole (0.75mg/kg), haloperidol (0.1mg/kg), olanzapine (0.5mg/kg), or vehicle, 3 times/day for 1 or 12 weeks. Western blotting was performed to examine the expression of NRG1 isoforms (135kDa, 70kDa and 40kDa) and ErbB4 receptors. Both 1-week haloperidol and olanzapine treatment increased NRG1-70kDa expression in the hippocampus; haloperidol also up-regulated ErbB4 levels in the prefrontal cortex (PFC). In the 12-week group, aripiprazole decreased the expression of all three NRG1 isoforms and ErbB4 receptors in the PFC, NRG1-70kDa and -40kDa in the cingulate cortex (Cg), and NRG1-135kDa, -70kDa and ErbB4 receptors in the hippocampus; haloperidol reduced NRG1-135kDa in the PFC, NRG1-40kDa in all three brain regions, and ErbB4 receptor levels in the PFC and hippocampus; NRG1-40kDa in the PFC and Cg was also down-regulated by olanzapine. These results suggest that the time-dependent and region-specific effects of antipsychotics on NRG1-ErbB4 signalling may contribute to the efficacy of antipsychotics to treat schizophrenia. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.Psychiatry Research 12/2014; DOI:10.1016/j.psychres.2014.12.014 · 2.68 Impact Factor