What is phenobarbital? How does it interact with other drugs?

Folate

Effect: Supplementation Possibly Helpful

Phenobarbital can reduce folate levels, perhaps by increasing the rate of
breakdown of the vitamin. Over time, such a decrease can cause anemia.
Taking folate supplements can correct this anemia.
Anticonvulsant-induced folate deficiency might also cause birth defects. Women who
plan to become pregnant while on phenobarbital should be sure to take a supplement
to prevent deficiency.

Vitamin D

Effect: Supplementation Possibly Helpful

Phenobarbital appears to interfere with the normal absorption or metabolism of
vitamin
D. In turn, this can impair calcium absorption. Making sure
to get enough vitamin D (and calcium) should help prevent any problems from
developing.

Vitamin K

Effect: Supplementation Helpful for Pregnant Women

Children born to women taking phenobarbital while pregnant may be deficient in
vitamin
K. This might lead to bleeding disorders and facial bone
abnormalities. Supplementing with vitamin K during pregnancy should help; however,
physician supervision is recommended.

Biotin

Effect: Supplementation Possibly Helpful, but Take at a Different Time of Day

Many antiseizure medications, including phenobarbital, are believed to interfere
with the absorption of biotin. For this reason, persons taking
phenobarbital may benefit from extra biotin. Biotin should be taken two to three
hours apart from antiseizure medication. One should not exceed the recommended
daily intake, because it is possible that too much biotin might interfere with the
effectiveness of the medication.

Dong Quai, St. John’s Wort

Effect: Possible Harmful Interaction

Phenobarbital has been reported to cause increased sensitivity to the sun,
amplifying the risk of sunburn or skin rash. Because St. John’s
wort and dong quai may also cause this problem,
taking them during treatment with this drug might add to this risk. One should use
sunscreen or wear protective clothing during sun exposure if taking one of these
herbs while using this anticonvulsant.

Ginkgo

Effect: Possible Harmful Interaction

The herb ginkgo (Ginkgo biloba) has been used to
treat Alzheimer’s disease and ordinary age-related memory loss, among many other
conditions. The possible harmful interaction involves potential contaminants in
ginkgo, not ginkgo itself.

One study found that a natural nerve toxin present in the seeds of Ginkgo biloba made its way into standardized ginkgo extracts prepared from the leaves. This toxin has been associated with convulsions and death in laboratory animals.

The detected amounts of this toxic substance are considered harmless. However, given the lack of satisfactory standardization of herbal formulations in the United States, it is possible that some batches of product might contain higher contents of the toxin, depending on the season of harvest. In light of these findings, taking a ginkgo product that happened to contain significant levels of the nerve toxin might theoretically prevent an anticonvulsant from working as well as expected.

Hops, Kava, Passionflower, Valerian

Effect: Possible Harmful Interaction

The herb kava (Piper methysticum) has a sedative
effect and is used for anxiety and insomnia. Combining kava with anticonvulsants,
which possess similar depressant effects, could result in add-on or excessive
physical depression, sedation, and impairment. Because of the potentially serious
consequences, one should avoid combining these herbs with anticonvulsants or other
drugs that also have sedative or depressant effects, such as phenobarbital, unless
advised by a physician.

Glutamine

Effect: Theoretical Harmful Interaction

Because phenobarbital works (at least in part) by blocking glutamate pathways in
the brain, high dosages of glutamine might possibly overwhelm the
drug and increase the risk of seizures.

Bibliography

Arenz, A., et al. “Occurrence of Neurotoxic 4’-O-Methylpyridoxine in Ginkgo biloba Leaves, Ginkgo Medications, and Japanese Ginkgo Food.” Planta Medica 62 (1996): 548-551.

Cornelissen, M., et al. “Supplementation of Vitamin K in Pregnant Women Receiving Anticonvulsant Therapy Prevents Neonatal Vitamin K Deficiency.” American Journal of Obstetrics and Gynecology 168 (1993): 884-888.

Kishi, T., et al. “Mechanism for Reduction of Serum Folate by Antiepileptic Drugs During Prolonged Therapy.” Journal of the Neurological Sciences 145 (1997): 109-112.

Lewis, D. P., et al. “Drug and Environmental Factors Associated with Adverse Pregnancy Outcomes: Part I–Antiepileptic Drugs, Contraceptives, Smoking, and Folate.” Annals of Pharmacotherapy 32 (1998): 802-817.