title: Pharmacokinetic interactions between the hormonal emergency contraception, levonorgestrel (Plan B), and Efavirenz.
abstract: OBJECTIVE
  Compare the Plan B levonorgestrel (LNG) area under the concentration- time curve (AUC(12)) prior to and with efavirenz (EFV). Design. Prospective, open-label, single-arm, equivalence study.
  
  
  METHODS
  Healthy HIV-negative subjects underwent 12 hr intensive pharmacokinetic (PK) sampling following single dose LNG alone and after 14 days of EFV. Geometric means, Geometric Mean Ratios, and 90% confidence intervals (CI) are reported for PK Parameters. T-tests were utilized. Clinical parameters and liver function tests (LFTs) were assessed.
  
  
  RESULTS
  24 women enrolled and 21 completed the study. With EFV, LNG AUC(12) was reduced 56% (95% CI: 49%, 62%) from 42.9 to 17.8 ng∗hr/mL, and maximum concentration (C(max)) was reduced 41% (95% CI: 33%, 50%) from 8.4 to 4.6 ng/mL. LNG was well tolerated with no grade 3 or 4 treatment-related toxicities.
  
  
  CONCLUSIONS
  EFV significantly reduced LNG exposures. Higher LNG doses may be required with EFV. These results reinforce the importance of effective contraception in women taking EFV.
authors.affiliation: Division of Infectious Diseases, University of Colorado Denver, Aurora, CO, USA. monica.carten@ucdenver.edu
authors.forename: Monica L
authors.initials: ML
authors.lastname: Carten
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Kiser
authors.forename: Awewura
authors.initials: A
authors.lastname: Kwara
authors.forename: Samantha
authors.initials: S
authors.lastname: Mawhinney
authors.forename: Susan
authors.initials: S
authors.lastname: Cu-Uvin
mesh_terms: D000328:Adult; D000480:Alkynes; D019380:Anti-HIV Agents / Q000493:pharmacokinetics*; D019540:Area Under Curve; D048588:Benzoxazines / Q000493:pharmacokinetics*; D003271:Contraceptive Agents, Female / Q000493:pharmacokinetics*; D003521:Cyclopropanes; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000493:pharmacokinetics*; D008875:Middle Aged; D011446:Prospective Studies; D013810:Therapeutic Equivalency; D055815:Young Adult
chemical_list: D000480:Alkynes; D019380:Anti-HIV Agents; D048588:Benzoxazines; D003271:Contraceptive Agents, Female; D003521:Cyclopropanes; D016912:Levonorgestrel; C098320:efavirenz