Folic Acid Drug Interactions

Certain medications may cause problems if taken together with folic acid. Drug interactions may occur if folic acid is taken in combination with methotrexate, phenytoin, or pyrimethamine. Folic acid could potentially decrease the effectiveness of these medications. To help minimize the risk of developing drug interactions with folic acid, be sure to talk to your healthcare provider if you are taking any other medicines.

 

An Introduction to Folic Acid Drug Interactions

Even though it is a vitamin, folic acid can potentially interact with a few different medicines. Some of the medicines that may lead to folic acid interactions include:
 
  • Methotrexate (Rheumatrex®, Trexall®)
  • Phenytoin (Dilantin®, Phenytek®) or fosphenytoin (Cerebyx®)
  • Pyrimethamine (Daraprim®).
     

Folic Acid Interactions Explained

The following sections explain in detail the potentially negative interactions that can occur when folic acid is combined with any of the drugs listed above.
 
 
Methotrexate (Rheumatrex, Trexall)
It is thought that folic acid may decrease the effectiveness of methotrexate for treating cancer. Folic acid doesn't seem to effect methotrexate for other uses (such as for rheumatoid arthritis). If you take methotrexate for cancer treatment, do not take folic acid supplements without your healthcare provider's approval and supervision.
 
Phenytoin (Dilantin, Phenytek) and Fosphenytoin (Cerebyx)
Sometimes, high doses of folic acid can decrease the effectiveness of phenytoin, increasing the risk of seizures. High doses of folic acid are often recommended for people taking phenytoin (since phenytoin decreases folic acid levels), especially during pregnancy. Your healthcare provider should monitor the level of phenytoin in your blood and adjust your phenytoin dosing as necessary if you add a high dose of folic acid. Do not take high doses of folic acid without your healthcare provider's approval.
(Folic Acid Drug Interactions Continued: Page 2)
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Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD;