From the Guidelines
Valproate can reduce the effectiveness of estrogen-containing birth control, potentially leading to unintended pregnancy, and women taking valproate who also use hormonal contraceptives should use additional contraceptive methods, such as condoms or an IUD, to minimize this risk. This interaction occurs because valproate induces liver enzymes that accelerate the metabolism of contraceptive hormones, lowering their blood levels and reducing their effectiveness 1. The concern is not only about the reduced efficacy of birth control but also about the potential for valproate to increase the risk of birth defects if pregnancy occurs, as it is a known teratogen.
Key Considerations
- The interaction between valproate and estrogen-containing contraceptives applies to all formulations of valproate (tablets, sprinkles, extended-release, liquid) and all estrogen-containing contraceptives (pills, patches, rings) 1.
- Women on valproate therapy should consult their healthcare provider about alternative contraceptive options or adjusting their birth control regimen to ensure effective contraception.
- Regular pregnancy testing may be advisable for women on this combination of medications to promptly identify any unintended pregnancies.
Mechanism and Evidence
The mechanism behind this interaction involves valproate's induction of liver enzymes, which in turn accelerates the metabolism of estrogen and progestin in hormonal contraceptives, leading to decreased blood levels of these hormones and reduced contraceptive effectiveness 1. Studies and guidelines, such as those from the U.S. Medical Eligibility Criteria for Contraceptive Use, highlight the importance of considering drug interactions when prescribing contraceptives, especially for women on anticonvulsant therapy like valproate 1.
Clinical Implications
Given the potential for reduced efficacy of estrogen-containing contraceptives in women taking valproate, it is crucial for healthcare providers to discuss alternative contraceptive methods with their patients, such as intrauterine devices (IUDs) or barrier methods, to prevent unintended pregnancies and the associated risks, particularly the risk of birth defects associated with valproate use during pregnancy.
From the FDA Drug Label
Administration of a single-dose of ethinyloestradiol (50 μg)/levonorgestrel (250 μg) to 6 women on valproate (200 mg BID) therapy for 2 months did not reveal any pharmacokinetic interaction The major interaction between valproate and estrogen-containing birth control is none reported in the provided drug label, as a study found no pharmacokinetic interaction between valproate and a single dose of ethinyloestradiol/levonorgestrel 2.
From the Research
Interactions between Valproate and Estrogen Containing Birth Control
- There is evidence to suggest that valproate does not have significant interactions with estrogen-containing birth control methods 3, 4.
- Studies have shown that women taking valproate can use combined oral contraceptives (COCs) without significant interactions 3.
- Additionally, it has been found that valproic acid (sodium valproate) does not interact with the combined oral contraceptive pill, progesterone-only pill, medroxyprogesterone injections, or levonorgestrel implants 4.
- However, it is essential to note that individual responses to medication interactions can vary, and healthcare providers should monitor patients for any potential interactions or adverse effects.
- The selection of a contraceptive method should be based on a discussion between the patient and clinician, considering the patient's tolerance for risk of pregnancy, menstrual bleeding changes, other risks, and personal values and preferences 5, 6.
- Other factors such as the patient's medical history, lifestyle, and preferences should also be taken into account when choosing a contraceptive method 7.