Methotrexate

This drug has been used for several decades in the treatment of cancer but it has found a second and important use in the treatment of chronic inflammatory conditions such as arthritis and psoriasis.  It acts by disrupting the metabolism of the B vitamin folic acid which is required particularly by rapidly dividing cells which are often central to the disease process.  Methotrexate can also produce serious side-effects due to the adverse effects on cells in the bone marrow and the gut wall both of which are also rapidly dividing.  These adverse effects are reduced by administering folic acid in careful amounts.

Advice for those on Methotrexate:

• Very often a supplement of folic acid needs to be given to prevent deficiency from developing.  This dose is often a single 5 mg tablet (available only on prescription) taken once per week but not on the day when methotrexate is also taken.
• It is unwise to take any supplement of vitamin B complex or multivitamin, which will typically contain 200 ug to 400 ug per daily dose, on the same day as taking
   methotrexate

Alterations to the diet or use of supplements may alter the dose of methotrexate required
 to produce a therapeutic effect.  In the US the recent fortification of foods with folic acid has been associated with a rise in the doses of methotrexate used in treating inflammatory disorders.