Methotrexate is a drug that belongs to a class of medications called antimetabolites. It was originally developed as a chemotherapeutic drug for the treatment of cancer.
It is a cytotoxic drug and is considered a “high alert” medication when it is used for non-cancer cases.
Currently, it is used in the treatment of cancer and to control the symptoms of autoimmune diseases like psoriasis and rheumatoid arthritis when other treatments have failed.
In cancer, it works by slowing or stopping the cancer cells from growing. In psoriasis and rheumatoid arthritis, it works by suppressing the immune system.
It is available in tablet, liquid, and injectable forms.
Uses
In adults, methotrexate is used in the treatment of the following conditions:
Chemotherapy. This drug is used in chemotherapy to treat cancers either alone in high doses or in combination with other drugs.
Autoimmune diseases. Being an immunosuppressant (suppresses the immune system of the body), it has been found to be beneficial in the treatment of autoimmune diseases like rheumatoid arthritis, psoriasis, psoriatic arthritis, vasculitis, and Crohn’s disease. However, its doses for these diseases are small
Pregnancy. It is used in the treatment of ectopic pregnancies and also to terminate pregnancies (for medical reasons) in the early stages.
In children, methotrexate is used to treat:
juvenile idiopathic arthritis
systemic lupus erythematosus (SLE)
juvenile dermatomyositis
vasculitis
uveitis
localized scleroderma.
It may be 3 to 12 weeks before you notice any improvement in your symptoms, and you should persist with taking the medicine. You should continue taking methotrexate even after your symptoms improve.
Mechanism of action
Methotrexate is an antimetabolite and immunosuppressant drug. It interferes with the uptake of essential nutrients by the body cells.
This results in the inhibition of the immune system causing decreased inflammation and slowing the progress of an autoimmune disease.
In psoriasis. Methotrexate is a strong drug. The US Food and Drug Administration (FDA) approved it to treat adults with severe psoriasis that is not controlled by topical treatments and phototherapy. This drug acts by suppressing the overactive immune system that causes psoriasis. It slows the growth of skin cells and stops scales from forming on the skin’s surface.
In rheumatoid arthritis. In the treatment of rheumatoid arthritis (RA), methotrexate inhibits the proliferation of the lymphocytes and other cells that cause inflammation in the joint. This reduces joint inflammation and symptoms.
In cancer. Methotrexate belongs to a group of chemotherapy drugs called antimetabolites. It stops the cells from making and repairing DNA, which is needed for the cancer cells to grow and multiply.
Methotrexate and Psoriasis
The oral form of Methotrexate is used to treat severe forms of psoriasis. Due to its depressive action on the T-cells of the immune system, it inhibits the overproduction of skin cells (which happens in psoriasis) and reduces inflammation. It is also beneficial in the treatment of psoriatic arthritis.
It is used to treat various types of psoriasis mainly pustular psoriasis, erythrodermic psoriasis, and widespread plaque psoriasis with good effect.
This drug can effectively treat:
Severe and disabling psoriasis
Erythrodermic psoriasis
Psoriatic arthritis
Nail psoriasis
Palmoplantar psoriasis
Methotrexate for Rheumatoid Arthritis
Besides being an immunosuppressant by which it reduces inflammation and halts the progress of autoimmune disease, methotrexate also belongs to a class of drugs referred to as DMARDs (disease-modifying anti-rheumatic drugs).
In the treatment of rheumatoid arthritis, methotrexate is used alone or in combination with other DMARDs such as etanercept, infliximab, and adalimumab. Combination therapy gives better results.
Dose of Methotrexate
Methotrexate is available in tablet and injectable form. In some cases, the injectable form is given by mouth.
Its dosage varies and the oral doses are given once a week in small doses of 5 mg to 15 mg. It is given once a week either singly or in divided doses over a 24-hour period.
Methotrexate injections are also available. Its injectable forms can be given intramuscularly, intravenously, by subcutaneous route or intrathecal route. Injections are also given in weekly doses.
Warning
When taking methotrexate, you should:
Avoid going out in the sun. But, if you have to, you must protect your skin from sunlight
You should not use sunlamps and tanning beds.
You should take these precautions to prevent sunburn and psoriasis flares.
Methotrexate Monitoring
It is necessary that patients who are taking methotrexate undergo certain blood tests every month or quarterly. These tests include complete blood count, liver function tests, and serum creatinine.
When on Methotrexate, you must take medical advice before taking penicillin and sulpha-based drugs.
Adverse Effects
Though tolerance to this drug in small doses is good, its side effects include an upset stomach, ulcerative stomatitis, fever, nausea, loss of appetite, hair loss (which is reversible after stopping methotrexate), and fatigue.
It also adversely affects the production of blood cells such as the RBCs, WBCs, and platelets. Due to its suppressing action on the immune system, the risks of infection are high.
Long-term use of this drug can rarely cause some serious medical side effects such as liver damage.
Due to its liver toxicity, one must avoid alcohol when on this drug, and periodic liver function tests (monthly or quarterly) may be necessary. The teratogenic toxicity of methotrexate is also well known and is explained below.
Rarely, it has been known to cause bone marrow depression and gastrointestinal disorders, especially when used with NSAIDs. You must avoid the use of methotrexate with these drugs including aspirin.
Methotrexate exhibits teratogenic toxicity – meaning it can harm or cause the death of the developing fetus in the mother’s womb if the pregnant mother is taking it.
It is, therefore, important that no conception takes place when on therapy with this drug and for a further three months after stopping this therapy. As methotrexate can affect the development of sperm, men should also take similar precautions.
