There are a number of prescription medicines available for treatment of psoriasis. The most commonly used prescription preparations are topical treatments (ie. they are used directly on the skin as creams, lotions or gels). How they are applied is particularly important. Your doctor or nurse will explain and demonstrate the quantities and the method of application to you.

Vitamin D analogues
Calcipotriol (Dovonex) is a vitamin D analogue, which slows down the turnover of cells in the skin. This preparation is very cosmetically acceptable, can be applied to normal skin at the edge of psoriatic plaques without burning and does not smell or stain the skin. It comes as an ointment, cream and scalp solution (which can also be very effective for psoriasis of the nailbeds). It may be prescribed alone, as a twice-daily application or in conjunction with another preparation such as a steroid in the morning and Dovonex in the evening. It is particularly good for psoriasis in the flexures.

Salicylic acid
Salicylic acid (2-10% formulations) help remove scales and crusts, and may be used alongside or before any of the other therapies outlined.

Dithranol
Dithranol is derived from a natural product, chrysarobin, the active constituent of Goa powder, derived from the bark of a Brazilian tree. It is an extremely effective treatment for chronic plaque psoriasis.

Its main disadvantage is that it stains the skin (temporarily) and clothes (permanently). It burns normal skin, so must be very carefully applied to the plaques only. Always start with a low concentration and gradually increase the strength.

There are two main ways it is used; as an outpatient it is usually prescribed as the product Dithrocream which is applied for 30 minutes and washed off. The strength of cream is increased according to the response. As an inpatient it is used as part of the Ingram regimen.

Topical corticosteroids
These are the mainstay of treatment for psoriasis of the face, flexures and genital area. They are often combined with coal tar. The quantity used must be carefully supervised to avoid unwanted side effects, which should not occur if used properly.

When used alone they usually just suppress the psoriasis rather than actually clearing it (like tar or dithranol). Since they are cosmetically acceptable, they may be prescribed for use in the morning when the patient has to wear smart clothes for work, etc. in conjunction with messier treatments for home use later.

The strength of steroid prescribed varies depending on the type and site of the psoriasis. The weakest steroid, hydrocortisone, in usually ineffective in the treatment of psoriasis when used alone but may be effective when combined with coal tar.

Steroid scalp solutions (and Dovonex scalp lotion) are an important part of the management of scalp psoriasis. They should be applied to the red base only, after the scale/crust has been removed. In certain types, such as palmoplantar pustular psoriasis, the strongest topical steroid, Dermovate, may be needed. Steroid preparations should not be shared with friends.

Retinoids
One of the newest preparations on the Irish market is a retinoid called tazarotene (Zorac). It is cosmetically acceptable being a clear gel. It is prescribed for mild to moderate psoriasis involving up to 10% of the body surface area. Treatment is conveniently required only once daily.

Written by Rosemary Coleman, MD FRCPI, Consultant Dermatologist

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