Systemic treatment

Extensive and inflamed psoriasis that is resistant to local treatment may require systemic treatment. A number of antimetabolite drugs (such as azathioprine and hydroxyurea) and immunosuppressive drugs (such as ciclosporin A) are effective, but the most widely used are methotrexate and acitretin.

Methotrexate inhibits folic acid synthesis during the S phase of mitosis and diminishes epidermal turnover in the lesions of psoriasis. Because it is hepatotoxic liver function has to be assessed initially and at regular intervals during treatment. The dosage must be monitored, and when a total of 1-5 g is reached a liver biopsy is indicated to exclude significant liver damage.

Although it is rare, bone marrow suppression can occur insidiously and rapidly in some patients. In order to detect this an initial test dose is followed by a full blood count. If this gives normal results a weekly dose of 7-5-15 mg is used. As it is excreted in the urine, the dose must be reduced if renal function is impaired. Aspirin and sulphonamides diminish plasma binding.

Before phototherapy After phototherapy

Methotrexate may interact with barbiturates, para-aminobenzoic acid, phenytoin, probenecid, phenylbutazone, oral contraceptives, and colchicine.

Acitretin is a vitamin A derivative that can be prescribed only in hospital in the United Kingdom. It is useful in pustular psoriasis and has some effect on other types of psoriasis. However, the effect is increased when combined with PUVA. Minor side effects include drying of the mucous membranes, crusting in the nose, itching, thinning of the hair, and erythema of the palms and nail folds. These are usually not severe and settle when treatment stops. More serious side effects include hepatotoxicity and raised lipid concentrations. Liver function tests and serum lipid (cholesterol and triglyceride) concentrations have to be carefully monitored. Etretinate is teratogenic and should only be taken by women during reproductive years if effective contraception is used during treatment and for two years afterwards, as the half life is 70-100 days.

Ciclosporin A is an immunosuppressant widely used following organ transplantation. It is effective in suppressing the inflammatory types of psoriasis. Blood tests should be carried out before starting treatment, particularly serum creatinine, urea, and electrolytes, as ciclosporin A can interfere with renal function.

Cosyntex Failing Control Psoriasis
Erythematous psoriasis suitable for methotrexate treatment, having failed to respond to phototherapy

Further reading

Lowe NJ. Managing your psoriasis. London: Master Media, 1993 Lowe NJ. Practical psoriasis therapy, 2nd ed. St Louis: Mosby, 1992

Psoriasis of the scalp

This condition can be very difficult to clear, particularly if there are thick scales

• 3% salicylic acid in a suitable base and left on for four to six hours or overnight and then washed out with a tar shampoo

• Dithranol preparations are effective but will tint blonde or red hair purple

• Steroid preparations can be used to control itching

Scalp psoriasis
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