title: The pharmacokinetic and pharmacodynamic consequences of the co-administration of lamotrigine and a combined oral contraceptive in healthy female subjects.
abstract: OBJECTIVE
  To assess the pharmacokinetic and pharmacodynamic effects of co-administration of a combined oral contraceptive (ethinyloestradiol plus levonorgestrel) and lamotrigine.
  
  
  METHODS
  Over a period of 130 days, healthy female subjects took lamotrigine (titrated up to 300 mg day(-1)) and the combined oral contraceptive, either individually or as co-therapy. Plasma ethinyloestradiol and levonorgestrel concentrations were measured in the presence and absence of lamotrigine, and serum lamotrigine concentrations were measured in the presence and absence of the combined oral contraceptive. Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, oestradiol and sex hormone binding globulin were also determined.
  
  
  RESULTS
  Of the 22 enrolled subjects, 16 had evaluable pharmacokinetic data. The mean (90% CI) ratios of lamotrigine area under the concentration-time curve from 0 to 24 h (AUC(0,24 h)) and maximum observed concentration (C(max)) of lamotrigine when it was given with the combined oral contraceptive and during monotherapy were 0.48 (0.44, 0.53) and 0.61 (0.57, 0.66), respectively. Ethinyloestradiol pharmacokinetics were unchanged by lamotrigine, the mean combined oral contraceptive + lamotrigine : combined oral contraceptive alone ratios (90% CI) of the AUC(0,24 h) and C(max) of levonorgestrel were 0.81 (0.76, 0.86) and 0.88 (0.82, 0.93), respectively. FSH and LH concentrations were increased (by 4.7-fold and 3.4-fold, respectively) in the presence of lamotrigine, but the low serum progesterone concentrations suggested that suppression of ovulation was maintained. Intermenstrual bleeding was reported by 7/22 (32%) of subjects during co-administration of lamotrigine and combined oral contraceptive.
  
  
  CONCLUSIONS
  A clinically relevant pharmacokinetic interaction was observed during co-administration of a combined oral contraceptive and lamotrigine. A dosage adjustment for lamotrigine may need to be considered when these agents are co-administered. A modest decrease in the plasma concentration of levonorgestrel was also observed but there was no corresponding hormonal evidence of ovulation.
authors.affiliation: GlaxoSmithKline, Harlow, United Kingdom. jssidhu008@hotmail.com
authors.forename: Jagdev
authors.initials: J
authors.lastname: Sidhu
authors.forename: Sarah
authors.initials: S
authors.lastname: Job
authors.forename: Sunita
authors.initials: S
authors.lastname: Singh
authors.forename: Richard
authors.initials: R
authors.lastname: Philipson
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000097:blood* / Q000494:pharmacology; D003277:Contraceptives, Oral, Combined / Q000097:blood* / Q000494:pharmacology; D004347:Drug Interactions; D004958:Estradiol / Q000097:blood; D004997:Ethinyl Estradiol / Q000097:blood / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006801:Humans; D000077213:Lamotrigine; D016912:Levonorgestrel / Q000097:blood / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood; D008875:Middle Aged; D010060:Ovulation / Q000187:drug effects; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism; D014227:Triazines / Q000097:blood* / Q000494:pharmacology
chemical_list: D000927:Anticonvulsants; D003277:Contraceptives, Oral, Combined; D012738:Sex Hormone-Binding Globulin; D014227:Triazines; D004997:Ethinyl Estradiol; D004958:Estradiol; D016912:Levonorgestrel; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D000077213:Lamotrigine