Folic acid, a water-soluble B-complex vitamin, helps your body produce and maintain new cells, especially blood cells and platelets. It also helps prevent mutations in DNA that may lead to cancer and treats folic acid deficiency and certain types of anemia. These supplemental doses may have interactions with other drugs, so speak with your doctor before taking folic acid as a medication. It should not be used if you have kidney disease, an infection, if you are an alcoholic, or if you have any type of anemia that is not diagnosed or confirmed.
5-fluorouracil
Fluorouracil is a cancer medication that interferes with cell growth. The topical form treats scaly overgrowths of skin and superficial basal cell carcinoma by causing the death of cells growing the fastest, such as abnormal skin cells. The injection interferes with the growth and spread of cancer cells and treats cancer of the colon, rectum, breast, stomach or pancreas. Co-administration with folate therapy may intensify the pharmacological actions and side effects of this drug. While enhancement of the drug may be advantageous for some cancer patients, it may also lead to increased toxicity. The combination can result in a higher incidence of diarrhea and conjunctivitis as well as fluorouracil toxicity, with symptoms of loss of appetite, severe mouth ulcerations, bloody diarrhea, vaginal bleeding and potential death.
Capecitabine
Another major drug interaction occurs with capecitabine, a cancer medication generally prescribed to treat breast cancer and colon or rectum cancer that has metastasized. Folic acid may increase the side effects of this drug, especially gastrointestinal problems such as diarrhea and vomiting.
Fosphenytoin, Phenobarbital and Primidone
These drugs act as anticonvulsants for people with seizures. Co-administration with folic acid might reduce their effectiveness. The body breaks down these drugs to get rid of them, and folic acid may serve as a cofactor in their metabolism, thus increasing how quickly the body clears them. There are also case reports describing breakthrough seizures following the addition of folic acid therapy.
Methotrexate
Methotrexate is a drug that interferes with the growth of certain quickly-reproducing cells, such as cancer cells, bone marrow cells and skin cells. It treats certain types of cancer, severe psoriasis and rheumatoid arthritis. Methotrexate works by decreasing the effects of folic acid in the body's cells and even reducing the amount of folic acid in the body. People taking methotrexate may need higher doses of supplemental folic acid as a result. However, combination with folic acid therapy may decrease the effectiveness of this drug on cancer treatments.
Pyrimethamine
There is also a moderate interaction with pyrimethamine, which treats parasite infection, malaria and toxoplasmosis. Folic acid might decrease the effectiveness of this drug.
Other Drugs
Other drugs may lower levels of folic acid by interfering with its absorption or reducing the body's ability to use this vitamin: antacids, H2 blockers, proton pump inhibitors, bile acid sequestrants, carbamazepine, NSAIDs, sulfasalazine, triamterene and birth control medications. When taken long-term, these medications may increase the body's need for folic acid. Folic acid also interferes with the absorption and effectiveness of tetracycline.
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