Antifolate

[1] Folic acid's primary function in the body is as a cofactor to various methyltransferases involved in serine, methionine, thymidine and purine biosynthesis.

Some such as proguanil, pyrimethamine and trimethoprim selectively inhibit folate's actions in microbial organisms such as bacteria, protozoa and fungi.

The antifolate action specifically targets the fast-dividing cells, and tend to have adverse effects on the bone marrow, skin, and hair.

Both high-folate diets and supplemental folic acid may help reduce the toxic side-effects of low-dose methotrexate without decreasing its effectiveness.

[8][9] Anyone taking low-dose methotrexate for the health problems listed above should consult with a physician about the need for a folic acid supplement.