What birth control options are suitable for a female patient of childbearing age with a history of seizure disorders, taking Phenytoin (antiepileptic medication)?

Phenytoin and Birth Control: Contraceptive Options for Women with Seizure Disorders

Women taking phenytoin should avoid combined hormonal contraceptives (pills, patches, rings) due to significant drug interactions that reduce contraceptive effectiveness, and instead use depot medroxyprogesterone acetate (DMPA/Depo-Provera), intrauterine devices (copper or levonorgestrel), or barrier methods as first-line options. 1

Critical Drug Interaction

Phenytoin is a potent enzyme-inducing antiepileptic drug that significantly reduces the effectiveness of hormonal contraceptives containing estrogen and progestin. 1, 2

• Phenytoin induces hepatic cytochrome P-450 enzymes, which accelerate the metabolism of both estrogen and progesterone, decreasing their plasma concentrations and contraceptive efficacy 1, 3
• The CDC U.S. Medical Eligibility Criteria classifies combined hormonal contraceptives (CHCs) as Category 3 for women on phenytoin—meaning the risks generally outweigh the benefits and the method is generally not recommended unless other methods are unavailable or unacceptable 1
• The FDA drug label for phenytoin explicitly states that "drugs whose efficacy is impaired by phenytoin include oral contraceptives" 2

Recommended Contraceptive Options

First-Line: Highly Effective Methods

Depot medroxyprogesterone acetate (DMPA/Depo-Provera) is classified as Category 1 (no restrictions) for women taking phenytoin because its effectiveness is NOT decreased by enzyme-inducing antiepileptic drugs. 1

• DMPA provides reliable contraception with failure rates <1% with perfect use 4
• The higher progestin dose in DMPA overcomes the enzyme-induction effect of phenytoin 1

Intrauterine devices (both copper and levonorgestrel) are Category 1 and highly effective options with failure rates <1%. 1, 4

• The levonorgestrel IUD (LNG-IUD) acts primarily through local mechanisms in the uterus, so systemic drug interactions with phenytoin are not clinically significant 1
• The copper IUD is completely non-hormonal and therefore has no drug interaction concerns 4
• Both IUD types may decrease menstrual bleeding, which can be beneficial 4

Etonogestrel implants are classified as Category 2 (advantages generally outweigh risks) for women on phenytoin, though effectiveness may be somewhat reduced. 1

• While phenytoin may reduce implant effectiveness, the high progestin levels from the implant still provide reasonable contraceptive protection 1
• This is a less preferred option compared to DMPA or IUDs due to potential reduced efficacy 1

Alternative Options

Progestin-only pills (POPs) are classified as Category 3 for women taking phenytoin—generally not recommended due to significantly reduced effectiveness. 1

• Phenytoin reduces POP effectiveness through enzyme induction 1
• If POPs must be used, women should be counseled about the increased pregnancy risk and consider backup barrier methods 1

Barrier methods (condoms, diaphragm, cervical cap) are Category 1 and have no drug interactions, but have higher typical-use failure rates (13-18%). 1

• These methods should be recommended as backup contraception when using methods with potential reduced efficacy 1
• Consistent and correct use of male latex condoms also reduces STI/HIV transmission risk 1

Critical Pregnancy Planning Considerations

Phenytoin is FDA Pregnancy Category D and carries significant teratogenic risks—women must use effective contraception or engage in active pregnancy planning. 2, 5

• In utero phenytoin exposure increases risks for congenital malformations 2-3 times above baseline 6
• Approximately 50% of pregnancies are unintended, making effective contraception critical for women taking phenytoin 5
• The FDA label explicitly warns that "all women of child-bearing age should talk to their healthcare provider about using other possible treatments instead of DILANTIN [phenytoin]. If the decision is made to use DILANTIN, you should use effective birth control (contraception)" 2

If pregnancy is planned, preconception counseling should occur with optimization of seizure control, consideration of switching to less teratogenic antiepileptic drugs if possible, and folic acid supplementation. 6, 7

• Folic acid supplementation should be provided before conception and during organogenesis 6
• Monotherapy at the lowest effective dose is preferred over polytherapy 6
• More than 90% of women with epilepsy receiving antiepileptic drugs during pregnancy deliver normal children, but risks must be discussed 6

Common Pitfalls to Avoid

Do not prescribe standard-dose combined hormonal contraceptives (≤35 μg ethinyl estradiol) to women taking phenytoin without counseling about significantly reduced effectiveness. 1

• Studies show that 60% of women with epilepsy using contraception choose oral contraceptives, and 89% of these have significant drug-drug interactions with their antiepileptic drugs 5
• If CHCs must be used despite recommendations against them, higher estrogen doses (≥50 μg ethinyl estradiol) may be considered, though this is still not ideal 3

Do not assume that seizure control will be adversely affected by hormonal contraception—concurrent use does not worsen seizure control. 3

Documentation of contraception or pregnancy planning is critically inadequate in clinical practice—less than 7% of women receive contraception counseling and only 18% receive pregnancy planning counseling. 5

• These discussions should occur at least annually for all women of childbearing age taking phenytoin 5

Emergency Contraception

Emergency contraception options remain available and should be discussed, with copper IUD being most effective, followed by ulipristal acetate or levonorgestrel. 1, 8

• The copper IUD can be inserted within 5 days of unprotected intercourse and is the most effective emergency contraception method 1
• Ulipristal acetate (30 mg single dose) or levonorgestrel (1.5 mg single dose) should be taken as soon as possible within 5 days 1
• Enzyme-inducing effects of phenytoin may theoretically reduce emergency contraceptive pill effectiveness, though data are limited 1