Coal tar with dithranol and salicylic acid

How it works

Dithranol is an antiproliferative agent that inhibits keratinocyte hyperproliferation, coal tar adds anti-inflammatory and antiscaling action, and salicylic acid is a keratolytic that removes scale and enhances penetration of the active agents.

Prescribing in practice

• Dithranol is a potent irritant that burns and stains normal skin, so it must be applied carefully to plaques only, kept off the face, flexures and genitals, and removed as directed; it stains skin purple-brown and permanently stains clothing, bathware and hair.
• Coal tar increases photosensitivity, so protect treated skin from sunlight and use caution with phototherapy.
• Avoid use on acute, inflamed, pustular or broken skin where irritation is likely.

Monitoring

No laboratory monitoring is needed; review the plaques for response and the surrounding normal skin for dithranol-induced burning or staining.

Counselling the patient

• Apply precisely to the psoriasis plaques only, avoid healthy skin, and wash your hands thoroughly afterwards.
• Expect staining of skin, hair, fabrics and the bath, and a tar smell.
• Stop and seek advice if normal skin becomes burnt, very red or sore.

Evidence & guidelines

Dithranol and coal tar preparations are long-established topical treatments for stable chronic plaque psoriasis and are included in NICE psoriasis guidance.