Cancers form when cells within the body multiply uncontrollably and abnormally. These cells then spread and destroy nearby tissues. Methotrexate works by preventing the cancer cells from dividing and multiplying. It does this by inhibiting the action of an enzyme called dihydrofolate reductase. This enzyme normally converts folic acid into a substance called tetrahydrofolic acid, which is essential for the synthesis of new genetic material (DNA) within cells. Cells are unable to divide, multiply and repair themselves without tetrahydrofolic acid to make new DNA. As methotrexate deprives cells of this nutrient it kills cancer cells and stops the cancer growing.
Unfortunately, methotrexate also affects the division of normal, healthy cells, particularly those that divide rapidly such as the cells lining the mouth and gut and cells in the bone marrow. For this reason, cancer chemotherapy using high doses of methotrexate is usually followed by a treatment called folinic acid rescue therapy. This involves giving tetrahydrofolic acid, in the form of folinic acid, usually 24 hours after the methotrexate. This bypasses the action of the methotrexate and allows normal cell division to recover. Normal healthy cells recover faster than cancer cells and this helps to prevent side effects. The aim is to progressively shrink the cancer over several cycles of chemotherapy, allowing normal cells to recover in between.
Methotrexate is used to treat a wide variety of cancers, including acute leukaemias, non-Hodgkin's lymphoma, soft tissue and bone cancers, and solid tumours, particularly breast, lung, head and neck, bladder, cervical, ovarian, and testicular cancers. It may be given by mouth or injection, depending on the dose, and is most commonly used in combination with other chemotherapy medicines.
Here are some common side effects:
- Blurred vision.
- Diarrhoea.
- Changes in mood.
- Drowsiness.
- Fatigue.
- Lung disorders.
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