title: Haloperidol half-life after chronic dosing.
abstract: In normal subjects after a single oral dose, haloperidol half-life has been reported to range 14.5-36.7 hours (or up to 1.5 days). After chronic administration, half-lives of up to 21 days have been reported. The objective of this study was to evaluate specific factors that might account for differences in haloperidol half-life in patients taking haloperidol chronically, including gender, age, weight, race, CYP2D6 and CYP3A5 genotypes, comedication, and smoking.Thirty-one patients were administered haloperidol for 4 weeks followed by a 1-week washout before administration of clozapine. Haloperidol plasma levels were measured weekly for at least 2 months after discontinuation. The geometric mean for haloperidol half-life and detectable levels duration were 3.9 and 13.8 days, respectively. Within 31 subjects, 58% (18/31) had half-lives <3 days (1.2-2.3 days) and 42% (13/31) had half-lives > or =3 days. Two of 3 patients with half-lives longer than 30 days (720 hours) and levels detectable >2 months had received haloperidol decanoate. Five patients who received haloperidol decanoate in the prior year were excluded from a comparison between patients with long haloperidol half-lives (> or =3 days, n = 10) and patients with short half-lives (<3 days, n = 16). The only significant difference between the two groups was that African-Americans (n = 4) were all found to have a long haloperidol half-life (P = 0.014). CYP3A5 genotype did not appear to influence haloperidol half-life but the two CYP2D6 poor metabolizer had half-lives > or =3 days. This study suggests that haloperidol half-life following repeated drug administration is substantially more prolonged than what has been observed after acute haloperidol administration.
authors.affiliation: Mental Health Research Center at Eastern State Hospital, Lexington, KY, USA. jdeleon@uky.edu
authors.forename: Jose
authors.initials: J
authors.lastname: de Leon
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Diaz
authors.forename: Peter
authors.initials: P
authors.lastname: Wedlund
authors.forename: Richard C
authors.initials: RC
authors.lastname: Josiassen
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Cooper
authors.forename: George M
authors.initials: GM
authors.lastname: Simpson
mesh_terms: D000328:Adult; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D004311:Double-Blind Method; D005260:Female; D006207:Half-Life; D006220:Haloperidol / Q000008:administration & dosage* / Q000097:blood* / Q000493:pharmacokinetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000097:blood / Q000188:drug therapy; D018709:Statistics, Nonparametric
chemical_list: D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; C510164:CYP3A5 protein, human; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; D006220:Haloperidol