Phenytoin, available as the brand Dilantin, is a prescription anticonvulsant medication. Although you might not think that vitamins can cause problems when taken with medicine, Dilantin and folic acid have important interactions with each other. Unlike some drug and supplement interactions, however, these effects don't mean you should avoid taking folic acid while on Dilantin.
Functions
Dilantin decreases abnormal activity in the brain. It controls certain types of seizure disorders, and it also prevents and treats seizures that may begin during or after surgery on the brain or the nervous system. In addition, doctors prescribe Dilantin to regulate cardiac arrhythmia. Folic acid is a B vitamin in synthetic form that is added to fortified foods and included in supplements. The natural form of this vitamin, folate, is found in food. Folic acid and folate are often used interchangeably. Folic acid is essential for many processes, including normal neurological function and development of red blood cells.
Interactions
Taking phenytoin decreases folate levels in the blood and may lead to macrocytic anemia, notes a study published in June 2005 in "Neurology." Phenytoin may cause reduced gastrointestinal absorption of this vitamin, inhibit folate transport in tissues and increase metabolism of folate in the liver. Adding folic acid as a supplement after folate levels drop causes further problems, however, as this lowers phenytoin levels in the blood.
Case Study
The June 2005 "Neurology" article describes a case study in which a patient with a well-controlled seizure disorder developed recurrent seizures after beginning folic acid therapy to treat macrocytic anemia. There was a significant reduction in phenytoin levels in the blood. It appears that folic acid is involved in the metabolism of phenytoin, so increased levels of folic acid can increase the rate at which this drug breaks down to be eliminated from the body.
Solution
Health care providers often underestimate the impact of adding folic acid to correct a deficiency when a patient is taking phenytoin, according to the "Neurology" study authors. Adjustments in phenytoin dosage may be necessary. Beginning therapy with both phenytoin and folic acid at the same time can help determine proper dosages and prevent these negative interactions, concludes a study published in the July-August 1995 issue of "The Annals of Pharmacotherapy."
References
- PubMed Health: Phenytoin
- MayoClinic.com: Folate
- "Neurology"; Seizures Following Reduction in Phenytoin Level After Orally Administered Folic Acid; Donald Lee Steinweg and Michael L. Bentley; June 2005
- "The Annals of Pharmacotherapy"; Phenytoin-Folic Acid Interaction; D.P. Lewis, et al.; July-August 1995
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