Tars and keratolytics

Tars are anti-inflammatory and antipruritic, and are safe and effective treatment options for most types of psoriasis. They are usually added to therapy when symptoms have been controlled using a topical corticosteroid. However, the colour and pungent odour of tars can limit patient adherence.

Liquor picis carbonis (LPC, or coal tar solution) is the preferred tar.

Tars are often combined with keratolytics (eg salicylic acid 3 to 8%) to help soften and lift scale. Tar preparations usually need to be extemporaneously prepared by a compounding pharmacy. Coal tar–based shampoos for scalp psoriasis are available over the counter in pharmacies.

Tar preparations can sting—do not use on excoriated or very inflamed skin. As a guide, for more sensitive skin (eg flexures, genitals), use lower concentrations of LPC alone (eg LPC 1 to 2%). For other areas of the body, start with LPC 4 to 8% and salicylic acid 3% in a cream base. For thick lesions, use higher concentrations of LPC and salicylic acid. Titrate the concentration of the active ingredients up or down, depending on response and tolerability. The maximum concentration is usually LPC 10% and salicylic acid 10%.

If LPC is not tolerated, trial ichthammol with salicylic acid, or salicylic acid alone.

If a tar preparation is used in combination with other topical treatments (eg topical corticosteroids, calcipotriol), apply the tar at night and the other preparation in the morning.