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Folic acid can interfere with certain chemotherapy drugs. Is there an acceptable level of folic acid or should it be avoided completely? Some foods, multivitamins, and supplements list folic acid as an active ingredient.

—Gloria Ramos-Awal, RN

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Folic acid, also known as vitamin B9, is necessary for many metabolic systems. The dietary nutrient is required for cell division and replication. Folic acid supplementation is necessary to prevent severe toxicities when receiving certain chemotherapy drugs such as pemetrexed (Alimta).

Coadministration of leucovorin (Fuseliv, generics), a folate analogue, with fluorouracil (5-FU) was shown to increase the effectiveness of 5-FU. Administration of folic acid in large doses, such as through supplements, can also cause increased toxicity in patients receiving capecitabine (Xeloda), an oral prodrug of 5-FU, with no increase in effectiveness. Therefore, patients receiving 5-FU or capecitabine are advised to avoid additional folic acid supplementation.

There are no clear guidelines on what is a safe amount of folic acid for patients who are receiving chemotherapy. Generally speaking, patients should not take additional folic acid or B vitamin supplements without first checking with their health care providers. The amounts of folic acid contained in most foods and vitamins are considered to be safe; however, patients should not take prenatal vitamins as they contain higher amounts of folic acid. ONA 

Lisa Thompson is assistant professor, Department of Clinical Pharmacy, University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences, Aurora, Colorado.