title: Cyclobenzaprine pharmacokinetics, including the effects of age, gender, and hepatic insufficiency.
abstract: The pharmacokinetics and bioavailability of cyclobenzaprine, a widely used muscle relaxant, were investigated in four clinical studies, and the effects of age, gender, and hepatic insufficiency were characterized. Cyclobenzaprine plasma clearance was 689 ml/min, and the bioavailability of a 5 mg oral dose was 0.55. Following oral doses of 2.5 to 10 mg tid in healthy young subjects, cyclobenzaprine pharmacokinetics were linear, and plasma concentrations generally increased proportional to dose. There was about a fourfold accumulation of the drug in plasma on multiple dosing, corresponding to an effective half-life of 18 hours. Steady-state plasma concentrations of cyclobenzaprine in elderly subjects were twice as high as in young subjects following oral doses of 5 mg tid. Steady-state plasma concentration also appeared to be up to twofold higher in subjects with mild hepatic insufficiency compared to healthy controls. The magnitude of any difference in steady-state plasma concentration between males and females appears to be small relative to intersubject variability. A reduction in dose or dosing frequency should be considered in the elderly and in patients with liver disease.
authors.affiliation: Merck Research Laboratories, West Point, Pennsylvania 19486, USA.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Winchell
authors.forename: Joyce D
authors.initials: JD
authors.lastname: King
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: Chavez-Eng
authors.forename: Marvin L
authors.initials: ML
authors.lastname: Constanzer
authors.forename: Scott H
authors.initials: SH
authors.lastname: Korn
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000367:Age Factors; D000368:Aged; D000639:Amitriptyline / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics*; D000704:Analysis of Variance; D019540:Area Under Curve; D001682:Biological Availability; D016001:Confidence Intervals; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008108:Liver Diseases, Alcoholic / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009125:Muscle Relaxants, Central / Q000097:blood / Q000493:pharmacokinetics*; D012737:Sex Factors
chemical_list: D009125:Muscle Relaxants, Central; D000639:Amitriptyline; C004704:cyclobenzaprine