Psoriasis - Topical Medications

Coal Tar

Coal tar preparations have been used for psoriasis for about 100 years although its use has declined with the introduction of topical vitamin D3 analogs. Crude coal tar inhibits enzymes that contribute to psoriasis and helps prevent cell proliferation. Tar is often used in combination with other drugs and with ultraviolet B (UVB) phototherapy.

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Side Effects. Preparations have the following drawbacks:

The drug can cause sun sensitivity and increase the risk for sunburn for up to 24 hours after use.
It has a strong smell.
It can stain clothing.
It irritates the skin.
Ingesting the medication is life threatening. In such cases poison control should be called immediately.

Anthralin

Benefits. Anthralin (Dritho-Scalp, Drithocreme, Micanol), called dithranol in Europe, is a derivative of a traditional medication called chyrsarobin, in use since the early 1900s. Anthralin slows skin cell reproduction and can produce remissions that last for months. It is recommended only for chronic or inactive psoriasis, not for acute or inflamed eruptions.

Side Effects. As with tar, its use has also declined with introduction of the vitamin D topical analogs, but newer formulations, such as Micanol, have made its use more tolerable. Micanol (Psoriatec) is an anthralin formulated in micro-capsules, which dissolve and allow the drug to be delivered directly to the target skin areas. It is particularly useful for scalp psoriasis, and it is less apt to stain, as standard anthralin does.

Skin irritation and burning. Anthralin should not be used on the face. Fair skinned people should generally avoid it. Triethanolamine (CuraStain) is a chemical that can neutralize anthralin and help reduce irritation from short-contact anthralin therapy. It should be applied a minute or two before washing off the anthralin. It is then reapplied after drying the skin.
Brown staining. Older forms of anthralin, such as Drithocreme, can stain hair, fabrics, plastics, and other household products. Micanol does not stain household products if used with cool water. Washing stained items with hypochlorite (Clorox) detergents can help remove stains.
Although topical preparations do not appear to affect areas other than the skin, people with kidney problems are advised to use anthralin with caution.

Application. Anthralin should be applied only to the psoriasis plaques. Many people use disposable gloves to avoid staining hands. The areas can usually be protected with dressings. Rub the cream in well and wipe off any excess. Wash off only with lukewarm water, not soap. (Using hot water will trigger the staining action.) A technique called short-contact anthralin therapy (SCAT), also called minute therapy, is useful for local areas of psoriasis. In such cases, anthralin is applied for only 10 minutes to an hour.