title: Pharmacokinetic and pharmacodynamic studies of the H1-receptor antagonist hydroxyzine in the elderly.
abstract: The pharmacokinetics and pharmacodynamics of the antipruritic H1-receptor antagonist hydroxyzine hydrochloride were studied in nine healthy, fasting subjects (mean age 69.5 +/- 3.7 years) who ingested a single dose of hydroxyzine syrup, 0.7 mg/kg (mean dose 49.0 +/- 6.7 mg). Blood samples were collected hourly for 6 hours, every 2 hours from 6 to 12 hours, at 24 hours, and then every 24 hours for 144 hours. At these times an intradermal injection of 0.01 ml of a 0.1 mg/ml histamine phosphate solution was performed, and wheal and flare areas were computed. The serum elimination t1/2 of hydroxyzine was 29.3 +/- 10.1 hours; the volume of distribution was 22.5 +/- 6.3 L/kg; the clearance rate was 9.6 +/- 3.2 ml/min/kg, and the AUC was 1383.1 +/- 1039.0 ng.hr/ml. The mean serum elimination t1/2 of cetirizine, the active metabolite of hydroxyzine generated in vivo, was 24.8 +/- 7.7 hours, not significantly different from that of the parent compound (p = 0.05). After a single dose of hydroxyzine the mean wheal and flare areas were significantly suppressed from 1 to 144 hours, compared with the mean predose wheal and flare sizes (p less than 0.01). Maximum wheal suppression, compared with all other wheals measured during the study, occurred from 4 to 10 hours, inclusive, and maximum flare suppression occurred from 2 to 72 hours, inclusive (p less than 0.01). Hydroxyzine has a long t1/2 and a large volume of distribution in the elderly. The suppressive effect on the wheal and flare after a single dose of hydroxyzine is also extremely prolonged, suggesting the possibility of enhanced H1-receptor activity in old age.
authors.affiliation: Faculty of Medicine, Health Sciences Clinical Research Centre, University of Manitoba, Winnipeg, Canada.
authors.forename: K J
authors.initials: KJ
authors.lastname: Simons
authors.forename: W T
authors.initials: WT
authors.lastname: Watson
authors.forename: X Y
authors.initials: XY
authors.lastname: Chen
authors.forename: F E
authors.initials: FE
authors.lastname: Simons
mesh_terms: D000367:Age Factors; D000368:Aged; D005260:Female; D006207:Half-Life; D006634:Histamine H1 Antagonists / Q000493:pharmacokinetics*; D006801:Humans; D006919:Hydroxyzine / Q000493:pharmacokinetics* / Q000494:pharmacology; D008297:Male
chemical_list: D006634:Histamine H1 Antagonists; D006919:Hydroxyzine