Methotrexate therapy for psoriasis- What is Methotrexate injection – Methotrexate psoriatic arthritis

Methotrexate (MTX) is a drug that acts to stop rapid or excessive cell growth – a ‘cytotoxic’ agent. It stops the rapid turnover of skin cells that cause the typical plaques of psoriasis. Unfortunately, it does not just act on the skin, so care has to be taken to avoid damage to other organs, especially the liver. It can also affect the bone marrow, where most of the blood cells are made, so regular tests are necessary to pick this up before it becomes a real problem. Methotrexate is a drug originally developed for the treatment of cancer

Both psoriasis and cancer, however, involve cells growing and multiplying more rapidly than they should, so the cytotoxic action of methotrexate has the same effect on those cells.

Damage to the liver can occur with the long-term use of methotrexate, but it can also affect the bone marrow and interfere with the production of blood cells. The drug tends to be used in low doses in psoriasis so does not cause many other problems. In the higher doses used in some cancer treatments (chemotherapy), it can have toxic effects on the lungs and gut.

Methotrexate can damage the liver, and as the side-effects are well known, doctors like to be able to avoid or prevent them. If you waited for signs of liver damage to show up in the blood, you might have developed long-term problems. The liver biopsy, which involves using a wide needle to take a small sample of the liver tissue, can show some very early and subtle changes before they do you any harm. There are, of course, some risks of having a liver biopsy, and you usually need to spend a day in hospital in case of internal bleeding; this added risk is taken into consideration when weighing up the pros and cons of using the treatment. Liver biopsies are not done very often, maybe only every couple of years depending on the dose you need.

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There are some problems with methotrexate and other drugs that you may be prescribed or buy over the counter that tend to make the methotrexate more toxic. The common drugs are trimethoprim (an antibiotic often used for urinary infections), phenytoin (a drug for epilepsy), aspirin and other anti-inflammatory drugs such as ibuprofen, some ‘water’ tablets (diuretics) used to treat high blood pressure and heart failure, and the retinoid drugs such as Neotigason.

Although methotrexate can be prescribed by GPs, it is a drug that they do not have to use very often and one that has potentially very serious side-effects. This means that GPs may not be happy to take the responsibility for prescribing it in case errors are made or they do not spot any potential problems soon enough.

This is the most common side-effect as up to 25% of people taking methotrexate may have the same problem as you. You have probably found that it comes on about 12 hours after taking the tablet and can last up to 3 days, so even though it is described as ‘mild’ in most cases, it can be a great nuisance. There are no surefire ways to stop the sick feeling (nausea), but the vitamin folic acid, taken every day, helps most people.

There are no problems with any of the topical treatments used in psoriasis. Drugs taken by mouth that might affect the immune system and UV light treatments should, however, be avoided.