Methotrexate (MTX) is one of most potent drugs used to control severe psoriasis and other skin diseases. It has been used for skin disease since the early 1960s. It was used initially to treat cancers. By chance, it was discovered to be effective in clearing psoriasis. For skin diseases it is used in much smaller doses. It is also used in rheumatoid arthritis and severe psoriatic arthritis.

MTX works best on extensive psoriasis, erythrodermic and acute pustular psoriasis, physically disabling psoriasis of the palms and soles, and psoriasis in the elderly. The majority of patients achieve significant or even complete clearing of their disease with MTX. The clearance or remission can last for a few weeks to a year or more after stopping therapy.

There are medical conditions and histories that may disqualify some patients from using MTX:

  • Women who are pregnant
  • Men or women who are trying to conceive a child
  • People who have blood disorders, including HIV/AIDS
  • People with an active peptic ulcer
  • People with severe anemia
  • People with cirrhosis of the liver
  • People with active hepatitis
  • People with significant liver or kidney abnormalities
  • People with active infectious disease
  • People who consume alcohol (beer, wine, liquor)
  • Patients who are unreliable

It is normally taken on a once weekly basis. The starting dose is approximately 7.5 – 10 mg weekly. The tablets take 2-3 weeks before a change is seen. If the drug cannot be tolerated orally, it can be given by injection.

MTX has several potential side effects. Some of the most common:

Nausea, especially when first used. The tablets can be divided up on the day of use to reduce this effect.
Mouth ulcers, this may be a sign of an excessive dose or a low white count.
Blood problems from marrow suppression, blood tests can check for this.
A potential for a type of liver cirrhosis or inflammation with damage, this is a cumulative dose effect. After certain doses are reached a liver biopsy is advisable.
A type of inflammation of the lung.
Hair loss
It is contraindicated in pregnancy as birth defects have been described. Planning of pregnancy is essential, and the Methotrexate should be stopped 3 months before conception. This applies also to males as well as females.
The side effects are increased by use of aspirin. Combining MTX with certain drugs, such as Bactrim, may be deadly.

For the most severe cases, methotrexate is used in combination with other drugs like cyclosporin, or with phototherapy (ultraviolet lights). As with any potent drug, side effects are possible, but the effect on ones life from the skin disease often outweighs the risk from the medication.