title: Nonresponse to clozapine and ultrarapid CYP1A2 activity: clinical data and analysis of CYP1A2 gene.
abstract: Clozapine (CLO), an atypical antipsychotic, depends mainly on cytochrome P450 1A2 (CYP1A2) for its metabolic clearance. Four patients treated with CLO, who were smokers, were nonresponders and had low plasma levels while receiving usual doses. Their plasma levels to dose ratios of CLO (median; range, 0.34; 0.22 to 0.40 ng x day/mL x mg) were significantly lower than ratios calculated from another study with 29 patients (0.75; 0.22 to 2.83 ng x day/mL x mg; P < 0.01). These patients were confirmed as being CYP1A2 ultrarapid metabolizers by the caffeine phenotyping test (median systemic caffeine plasma clearance; range, 3.85; 3.33 to 4.17 mL/min/kg) when compared with previous studies (0.3 to 3.33 mL/min/kg). The sequencing of the entire CYP1A2 gene from genomic DNA of these patients suggests that the -164C > A mutation (CYP1A2*1F) in intron 1, which confers a high inducibility of CYP1A2 in smokers, is the most likely explanation for their ultrarapid CYP1A2 activity. A marked (2 patients) or a moderate (2 patients) improvement of the clinical state of the patients occurred after the increase of CLO blood levels above the therapeutic threshold by the increase of CLO doses to very high values (ie, up to 1400 mg/d) or by the introduction of fluvoxamine, a potent CYP1A2 inhibitor, at low dosage (50 to 100 mg/d). Due to the high frequency of smokers among patients with schizophrenia and to the high frequency of the -164C > A polymorphism, CYP1A2 genotyping could have important clinical implications for the treatment of patients with CLO.
authors.affiliation: Unité de Biochimie et Psychopharmacologie Clinique, Département Universitaire de Psychiatrie Adulte, Hôpital de Cery, Prilly-Lausanne, Switzerland. Chin.Eap@inst.hospvd.ch
authors.forename: Chin B
authors.initials: CB
authors.lastname: Eap
authors.forename: Stefan
authors.initials: S
authors.lastname: Bender
authors.forename: E
authors.initials: E
authors.lastname: Jaquenoud Sirot
authors.forename: Gianni
authors.initials: G
authors.lastname: Cucchia
authors.forename: Michèle
authors.initials: M
authors.lastname: Jonzier-Perey
authors.forename: Pierre
authors.initials: P
authors.lastname: Baumann
authors.forename: Delphine
authors.initials: D
authors.lastname: Allorge
authors.forename: Franck
authors.initials: F
authors.lastname: Broly
mesh_terms: D000328:Adult; D014150:Antipsychotic Agents / Q000097:blood / Q000627:therapeutic use*; D002110:Caffeine / Q000378:metabolism; D002849:Chromatography, Gas; D003024:Clozapine / Q000097:blood / Q000627:therapeutic use*; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics* / Q000378:metabolism*; D004247:DNA / Q000235:genetics; D004351:Drug Resistance; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D009154:Mutation / Q000235:genetics / Q000502:physiology; D010641:Phenotype; D011618:Psychotic Disorders / Q000188:drug therapy* / Q000235:genetics*; D012907:Smoking / Q000378:metabolism; D016896:Treatment Outcome
chemical_list: D014150:Antipsychotic Agents; D002110:Caffeine; D004247:DNA; D019388:Cytochrome P-450 CYP1A2; D003024:Clozapine