Abstract
To examine the genetic factors influencing clozapine kinetics in vivo, 75 patients treated with clozapine were genotyped for CYPs and ABCB1 polymorphisms and phenotyped for CYP1A2 and CYP3A activity. CYP1A2 activity and dose-corrected trough steady-state plasma concentrations of clozapine correlated significantly (r = -0.61; P = 1 x 10), with no influence of the CYP1A2*1F genotype (P = 0.38). CYP2C19 poor metabolizers (*2/*2 genotype) had 2.3-fold higher (P = 0.036) clozapine concentrations than the extensive metabolizers (non-*2/*2). In patients comedicated with fluvoxamine, a strong CYP1A2 inhibitor, clozapine and norclozapine concentrations correlate with CYP3A activity (r = 0.44, P = 0.075; r = 0.63, P = 0.007, respectively). Carriers of the ABCB1 3435TT genotype had a 1.6-fold higher clozapine plasma concentrations than noncarriers (P = 0.046). In conclusion, this study has shown for the first time a significant in vivo role of CYP2C19 and the P-gp transporter in the pharmacokinetics of clozapine. CYP1A2 is the main CYP isoform involved in clozapine metabolism, with CYP2C19 contributing moderately, and CYP3A4 contributing only in patients with reduced CYP1A2 activity. In addition, ABCB1, but not CYP2B6, CYP2C9, CYP2D6, CYP3A5, nor CYP3A7 polymorphisms, influence clozapine pharmacokinetics.
Publication types
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Clinical Trial
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Multicenter Study
MeSH terms
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ATP Binding Cassette Transporter, Subfamily B
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ATP Binding Cassette Transporter, Subfamily B, Member 1 / genetics*
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ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism
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Adult
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Aged
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Aged, 80 and over
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Antipsychotic Agents / administration & dosage
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Antipsychotic Agents / blood
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Antipsychotic Agents / pharmacokinetics*
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Aryl Hydrocarbon Hydroxylases / genetics*
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Caffeine / metabolism
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Clozapine / administration & dosage
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Clozapine / analogs & derivatives
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Clozapine / blood
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Clozapine / pharmacokinetics*
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Cytochrome P-450 CYP1A2 / genetics
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Cytochrome P-450 CYP2C19
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Cytochrome P-450 CYP3A
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Cytochrome P-450 Enzyme Inhibitors
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Cytochrome P-450 Enzyme System / genetics*
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Cytochrome P-450 Enzyme System / metabolism
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Enzyme Inhibitors / administration & dosage
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Female
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Fluvoxamine / administration & dosage
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Genotype
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Humans
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Male
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Midazolam / metabolism
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Middle Aged
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Phenotype
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Polymorphism, Genetic*
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Substrate Specificity
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Switzerland
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Young Adult
Substances
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ABCB1 protein, human
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ATP Binding Cassette Transporter, Subfamily B
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ATP Binding Cassette Transporter, Subfamily B, Member 1
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Antipsychotic Agents
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Cytochrome P-450 Enzyme Inhibitors
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Enzyme Inhibitors
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norclozapine
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Caffeine
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Cytochrome P-450 Enzyme System
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Aryl Hydrocarbon Hydroxylases
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CYP1A2 protein, human
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CYP2C19 protein, human
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CYP3A protein, human
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Cytochrome P-450 CYP1A2
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Cytochrome P-450 CYP2C19
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Cytochrome P-450 CYP3A
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Clozapine
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Fluvoxamine
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Midazolam