A Deeper Shade of Blue

Over the last decade, anticonvulsant medications or anti-epileptic drugs (AEDs) have been used more frequently in women of reproductive age. While this class of medications may be particularly helpful for the treatment of bipolar disorder and other mood disorders, they have significant interactions with other drugs. Many anticonvulsants induce liver enzymes and thus may enhance the metabolism of other drugs, including oral contraceptives.

The estrogen and progestins contained in oral contraceptives are metabolized by the liver. Anticonvulsants that induce liver enzymes may thus lower estrogen and progesterone levels, and may result in oral contraceptive failure. The following enzyme-inducing anticonvulsants hay decrease oral contraceptive effectiveness:

• Carbamazepine (Tegretol)
• Felbamate (Felbatol)
• Oxcarbazepine (Trileptal)
• Phenobarbital
• Phenytoin (Dilantin)
• Primidone (Mysoline)
• Topiramate (Topamax)

In a recent review, Dr. Mary Zupanc at the Medical College of Wisconsin made the following recommendations regarding the use of oral contraceptives in women taking anticonvulsants:

Hormonal contraception appears to remain effective in patients treated with AEDs that do not induce hepatic microsomal enzymes. The typical failure rate of oral contraceptive pills is <5%, whereas the typical failure rate of other forms of hormonal contraception is <1%. Other contraceptive methods, including barrier methods, have higher typical failure rates (intrauterine device 3%; barrier methods 12% to 18%). Given these failure rates and the greater risk for birth defects in women with epilepsy, patients require education about the possible teratogenic effects of AEDs, the consequent increased risk for birth defects, and the need for routine supplementation with adequate levels of folic acid. Patients for whom an unplanned pregnancy is simply unacceptable should consider using backup contraceptive methods to ensure protection.

Patients receiving enzyme-inducing AEDs may still choose concurrent hormonal contraception. Hormonal contraceptives with higher estrogen doses are recommended for such patients to compensate for the hormone’s increased metabolism. An estrogen dose of at least 50 µg is preferred. However, few higher-dose oral contraceptives are available at present.

Other psychotropic medications associated with oral contraceptive failure include:

• Modafinil (Provigil)
• St. John’s wort

If you are prescribed an oral contraceptive, let your doctor know about all the medications you are taking, including prescriptions, over-the-counter medications, herbs, vitamins, and supplements.