A patient with rheumatoid arthritis was prescribed Tab
Methotrexate 5mg per week and Tab Folic acid 5mg per day. I know that methotrexate
blocks the conversion of folic acid to folinic acid and hence can inhibit the
action of certain important enzymes in the body.
I asked myself two questions:
- Is folic acid really necessary when prescribing low dose long term methotrexate?
- Will folic acid reduce the efficacy of methotrexate?
A Medscape article provided the
answers. Low dose methotrexate refers to the use of less than 20mg of
methotrexate per week. Studies have shown that folic acid supplementation has a
beneficial effect in reducing the side effects of methotrexate like stomatitis,
gastrointestinal upsets, liver dysfunction and bone marrow suppression. Folinic
acid too has the same benefit but it is more expensive. It is not entirely
clear whether folic acid supplementation will reduce the efficacy of
methotrexate in rheumatoid arthritis but it probably will not. The beneficial
effect of low dose methotrexate in rheumatoid arthritis appears not to be related
to its inhibition of folic acid metabolism.
A cardiovascular benefit in
providing supplementation with folic acid is also present. Methotrexate tends
to increase homocysteine levels (a cardiovascular risk factor) in the blood. This
will be prevented by folic acid.
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