title: Pharmacokinetics of single-dose levonorgestrel in adolescents.
abstract: OBJECTIVE
  The purpose of this study is to compare the pharmacokinetics of levonorgestrel, a drug used for emergency contraception between female adolescents and adults.
  
  
  METHODS
  Twenty-two female subjects, aged 13-16 years, received a single 0.75-mg dose of the drug. Serial blood samples were collected for 72 h and used to measure plasma levonorgestrel concentrations. Previously published data from 16 adults, aged 18-45 years, served as comparison.
  
  
  RESULTS
  There was a statistically significant higher total plasma clearance divided by the bioavailability (CL/F) of levonorgestrel in adolescents compared to adults, resulting in lower maximum and average total plasma concentrations. There was a trend for a larger volume of distribution divided by bioavailability (V/F), but there was no significant difference in the half-life of levonorgestrel in adolescents relative to adults (p=.098).
  
  
  CONCLUSIONS
  The differences between adolescents and adults are unlikely to be clinically significant because specific changes in total concentrations suggest that unbound concentrations are probably not affected. Furthermore, empirically high doses of levonorgestrel are given for emergency contraception.
authors.affiliation: Department of Biopharmaceutical Sciences, School of Pharmacy, University of California San Francisco, Box 0446, San Francisco, CA 94143-0446, USA. nancy.sambol@ucsf.edu
authors.forename: Nancy C
authors.initials: NC
authors.lastname: Sambol
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Harper
authors.forename: Lena
authors.initials: L
authors.lastname: Kim
authors.forename: Chui Yu
authors.initials: CY
authors.lastname: Liu
authors.forename: Philip
authors.initials: P
authors.lastname: Darney
authors.forename: Tina R
authors.initials: TR
authors.lastname: Raine
mesh_terms: D000293:Adolescent; D001682:Biological Availability; D003280:Contraceptives, Oral, Synthetic / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007700:Kinetics; D016912:Levonorgestrel / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D011446:Prospective Studies; D012044:Regression Analysis
chemical_list: D003280:Contraceptives, Oral, Synthetic; D016912:Levonorgestrel