Drug-Drug Interaction

CARBAMAZEPINE; RUFINAMIDE/HORMONAL CONTRACEPTIVES

MECHANISM OF ACTION
Carbamazepine and rufinamide may increase the hepatic metabolism of hormonal contraceptives.

DISCUSSION
In a study of four epileptic patients receiving an oral contraceptive containing ethinyl estradiol 50 mcg plus levonorgestrel 250 mcg carbamazepine reduced the area-under-curve (AUC) for ethinyl estradiol by 42% and for levonorgestrel by 40%. Pregnancy has been reported

CLINICAL EFFECTS
Concurrent use with carbamazepine or rufinamide may result in decreased contraceptive levels, which may result in menstrual abnormalities and unintended pregnancy.

SEVERITY LEVEL
2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

PATIENT MANAGEMENT
In individuals wanting to avoid pregnancy, alternative or additional means of contraception should be utilized.

PREDISPOSING FACTORS
None determined.

REFERENCES

  1. Rapport DJ, Calabrese JR. Interactions between carbamazepine and birth .Rapport DJ, Calabrese JR. Interactions between carbamazepine and birth control pills. Psychosomatics 1989 Fall;30(4):462-4.
  2. Crawford P, Chadwick DJ, Martin C, Tjia J, Back DJ, Orme M. The .Crawford P, Chadwick DJ, Martin C, Tjia J, Back DJ, Orme M. The interaction of phenytoin and carbamazepine with combined oral contraceptive steroids. Br J Clin Pharmacol 1990 Dec;30(6):892-6.
  3. Nor-Q-D (norethindrone) US prescribing information. WatsonPharma March, .Nor-Q-D (norethindrone) US prescribing information. WatsonPharma March, 2005.
  4. Doose DR, Wang SS, Padmanabhan M, Schwabe S, Jacobs D, Bialer M. Effect of .Doose DR, Wang SS, Padmanabhan M, Schwabe S, Jacobs D, Bialer M. Effect of topiramate or carbamazepine on the pharmacokinetics of an oral contraceptive containing norethindrone and ethinyl estradiol in healthy obese and nonobese female subjects. Epilepsia 2003 Apr;44(4):540-9.
  5. Inovelon (rufinamide) UK summary of product characteristics. Eisai Limited .Inovelon (rufinamide) UK summary of product characteristics. Eisai Limited January 16, 2007.