Dithranol

Dithranol (INN) or Anthralin (USAN and former BAN) is a Hydroxyanthrone, anthracene derivative, medicine applied to the skin of people with psoriasis. It is available as creams, ointment or pastes in 0.1 to 2% stengths (Dithrocream®, Micanol® and Psorlin®).

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Pharmacology

Dithranol accumulates in mitochondria where it interferes with the supply of energy to the cell, probably by the oxidation of dithranol releasing free radicals. This impedes DNA replication and so slows the excessive cell division that occurs in psoriatic plaques. In addition Dithranol may act by reducing the elevated levels of cGMP that occurs in psoriasis.

More dithranol penetrates into impaired skin in 30 minutes than into intact skin during about 16 hours. For this reason weaker 0.1-0.5% preparations are applied over night, but stronger 1-2% products are applied for between 30 minutes and one hour depending upon the formulation.

Clinical considerations

Dithranol has a slower onset of action in controlling psoriasis, typically several weeks, compared to glucocorticoid steroids, but is without the potential for rebound reaction on withdrawal. It cannot be used on the face or genitalia.

Side effects

It temporarily stains the skin a yellowy-brown and permanently stains clothing fabrics. It may cause a local burning sensation and irritation, this may be minimised by careful attention to the details of treatment and only gradually stepping up through the strengths of dithranol formulations. The surrounding skin can be protected using soft white paraffin and the treated area is covered with tube gauze.

References

• Anthralin Treatment of Psoriasis The Skin Site
• British National Formulary 45 March 2003
• Micanol data sheet. New Zealand Medicines and Medical Devices Safety Authority (2 May 2001).