Doctors have repurposed some chemotherapy drugs to treat psoriasis, including methotrexate and photochemotherapy. Doctors will use lower dosages of these drugs to treat psoriasis than they would to treat cancer.

Psoriasis is a debilitating inflammatory condition, ranging from small areas of raised skin to severe patches covering larger parts of the body. This condition can also cause painful joints, referred to as psoriatic arthritis.

Applying lotions or ointments to the affected area is the first-line treatment for mild-to-moderate cases of psoriasis. These topical treatments may be corticosteroids. Other therapies include vitamin D analogs and phototherapy. If the condition is moderate-to-severe, a person will require injections or oral treatments.

At present, there is no cure for psoriasis. However, treatment can help manage symptoms, and people with psoriasis can go into remission. Medical professionals will explain the possible treatment options and side effects of the prescribed drugs.

In this article, we examine the use of methotrexate and photochemotherapy for treating psoriasis. We also look at side effects and other treatment options.

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Methotrexate is a common initial treatment for psoriasis and has been for a long time. Doctors prescribe it at a lower dose than they would for a person with cancer, alongside folic acid to reduce adverse reactions to the drug.

A 2016 meta-analysis of methotrexate use for psoriasis showed that 45.2% of people achieved a three-quarters reduction in the percentage affected area by 12–16 weeks.

Methotrexate is available as an injection or a tablet form. It is essential to consult a doctor or pharmacist regarding the recommended dosage.

Injection

The recommended dosage for a person with psoriasis is 10–25 milligrams (mg) once weekly. The dosage is adjusted gradually to achieve optimal clinical response. Doctors advise people not to exceed 25 mg per week.

Tablet

The initial recommended dose is 7.5–10 mg per week, which doctors may increase to a maximum of 25 mg per week.

Each tablet is 2.5 mg. People usually take a single dose of tablets once per week.

People cannot use methotrexate in the following cases:

In a 2016 meta-analysis, the adverse effects of methotrexate limited treatment in around 7% of cases.

Methotrexate can also create severe but rare reactions, including damage to the following organs:

Methotrexate may also cause some issues when mixed with other drugs and substances, including:

Photochemotherapy (PUVA) combines the administration of psoralens, which are plant-derived or synthetic compounds, with exposure to UVA radiation. Psoralen makes the skin more sensitive to light. This combination therapy is more effective than using UVA light alone.

Doctors often use PUVA as a treatment when psoriasis covers more than 20% of the body, which they consider a severe case.

Photochemotherapy treatment

Healthcare professionals will consider PUVA when previous treatments have failed to clear psoriasis or when the duration of remission is short.

Doctors administer this treatment in two phases: an initial clearing phase and a maintenance phase. During the initial phase, there will be two to three sessions of treatments per week, with a minimum of 48 hours between each session. It may take 25–30 visits for remission to occur, depending on the severity of the condition.

A person will then undertake maintenance sessions when psoriasis begins to clear. However, people may need to return to treatment if the psoriasis flares.

Research suggests PUVA combination therapy is 80% effective at reducing the severity of psoriasis.

While PUVA can be effective, it also carries possible risks.

People should not miss appointments as this can make the treatment less effective. Because UVA exposure can cause cataracts, people are required to wear safety goggles during treatment. A person should keep their doctor updated with the medications that they are taking for other conditions.

Usually, after treatment, the skin may appear slightly flushed or darker, but other side effects on the skin may include:

  • dark spots appearing
  • mild burning or stinging
  • itching
  • blisters or a burn

Possible long-term side effects may include:

A person should not use PUVA if they:

  • have skin cancer, or a medical condition that could make people more likely to develop skin cancer
  • have a medical condition that could make people more sensitive to UV light, such as lupus
  • are taking medication that increases sensitivity to UV light, including some skin creams
  • have a heart or brain condition
  • are pregnant, although PUVA will not cause a problem for future pregnancies once the person has finished treatment

Treating side effects of PUVA

PUVA can increase the risk of developing skin cancer. Doctors may check the skin of a person undergoing PUVA for signs of skin cancer.

People undergoing this treatment should avoid the following:

  • using a sunbed during treatment
  • going out into the sun without appropriate strong protection in the form of sunscreen and clothing
  • exposing their skin to the sun on the day of treatment

If people attending PUVA appointments develop dry, itchy skin, they should use emollients such as aqueous cream to help soothe the area. A person should also avoid using chemical products that increase sensitivity to the sun, including perfume, aftershave, and some deodorants.

There are several alternative options to chemotherapy when it comes to treating psoriasis. These include other drugs and light therapy.

Alternative drugs

While methotrexate may be a first treatment choice for psoriasis, other drugs are as effective or even more effective. Other treatments used for inflammatory conditions, such as rheumatoid arthritis, include:

Light therapies

Other light therapies are available to treat psoriasis. The recommended treatment may depend on the type and severity of psoriasis. Some of these include:

  • Narrowband ultraviolet B (NB-UVB): This treatment is more effective for larger areas of psoriatic lesions.
  • Pulsed dye laser: This therapy is effective for nail psoriasis and topical plaque psoriasis.
  • Photodynamic therapy, intense pulsed light: This treatment is effective for chronic plaque psoriasis and nail psoriasis.
  • Light-emitting diodes: This therapy is effective for chronic plaque psoriasis and nail psoriasis.
  • Red and blue light near-infrared: Doctors use these treatments to treat plaque psoriasis.
  • Excimer laser or lamp: This therapy is effective for nail psoriasis.
  • Broadband ultraviolet B: This treatment is generally safer than PUVA but may not be as effective for more severe psoriasis.
  • Sunbath: This therapy is effective for chronic plaque psoriasis.

Both PUVA and NB-UVB are effective therapies in psoriasis. However, considering the potential risks, dermatologists prefer NB-UVB as the first-line phototherapy.

Doctors have repurposed chemotherapy drugs to treat moderate-to-severe psoriasis so that people can go into remission. However, doctors typically use a lower dosage than when they are treating cancer.

Although there is currently no cure for psoriasis, effective treatments help reduce the symptoms of the condition.

It is also possible to manage the side effects of prescribed drugs with the help of a medical professional. Most people living with psoriasis can find a treatment that will help improve their quality of life.