Dithranol

Also known as anthralin, the active ingredients were originally extracted from the bark of the Brazilian araroba tree. During World War I a synthetic version was synthesised.

Dithranol affects the synthesis of cell DNA and has a pronounced anti-proliferative effect. It also appears to have a rapid effect on the normalisation of epidermal differentiation. In both these ways, it is an effective treatment for psoriasis. However, it does have a number of side effects including irritation and staining, although it has the advantage of being odourless. Its effects may be enhanced by the use of the Ingram regime, which includes UVB as well as topical treatment.

Method of application
In order for dithranol to be most effective, it must be carefully applied. Dithranol in a zinc oxide paste is most commonly used in hospital/ day-care facilities. The initial concentration is 0.1% and this in increased every 2–3 days (or according to how well the patient will tolerate it). Here the preparation is carefully applied to the plaques using a spatula and then ‘fixed’ using talc which is applied using a makeshift powder puff. This helps to keep the paste in place and minimises smudging onto good skin. This can then be covered with stocking net bandages and left in place for up to 24 hours. Removal of the paste can be difficult if just water is used; cotton wool soaked in a mineral oil is effective at removing the dithranol prior to getting in the bath.

Dithranol can be used on an outpatient basis, but is probably only useful if limited large plaques are present and the patient is well motivated. In this instance, short-contact dithranol can be used. A cream-based product (again starting at 0.1%) is carefully applied to the plaques using a gloved finger or cotton bud and left in place for any period up to an hour. The amount to be applied is sufficient to cover the plaque and be rubbed in, but not excessively or the chance of the product rubbing off onto clothes and furnishing is increased. At the lower strengths, patients might be able to tolerate leaving the product on overnight. Patients should gradually increase the strength of product used and the amount of time it is left on (starting at 10 minutes and working up to an hour). When the strength is increased, the amount of time it is left on should be temporarily decreased. It is possible to use this on the scalp; however as with the skin, the product can stain hair, particularly if blonde.

For both methods of application this is a once-daily treatment. The products should not be applied to sensitive areas, e.g. face or flexures or to sore or pustular psoriasis. Dithranol itself can cause soreness; if this is prolonged, the strength should be reduced or the amount of time left on decreased. If this does not resolve the problem, the treatment has to be stopped.