Cantharadin

What is Cantharidin?

Cantharidin is a vesicant that is used to deliberately create a blister on skin where there is an unwanted growth. The blister lifts the growth (such as a wart) off the skin. As the blister dries and peels off over the next week, the growth will peel off with it. The action of cantharidin does not go beyond the top layer of the skin (known as the epidermis), therefore it does not cause scarring.

What are the benefits of Cantharidin?

It is a painless treatment and therefore the preferred method of treating warts and mollusca in children and those that can’t tolerate other treatments.

It is also much faster at treating warts than other measures such as cryotherapy. Usually only 1- 2 treatments, a week or two apart is required to get rid of lesions unlike months of treatments with over-the-counter wart creams or cryotherapy. It is less likely to scar than other treatments such as cryotherapy.

When to use Cantharidin?

common viral warts
molluscum contagiosum

Both of these are caused by viruses that result in small, harmless growths on the skin.

When not to use cantharidin?

Cantharidin should not be used if there is an active bacterial skin infection.
Cantharidin should only be used with caution near mucous areas (mouth, eyes, genitals, etc).

What are the steps involved in cantharidin treatment?

Due to the potential for significant harm if used incorrectly, cantharidin treatment should be carried out by a doctor in a clinic setting rather than applied at home by a patient.

The steps to cantharidin treatment are below:

The skin overlying the wart is pared back (not required for molluscum).
Surrounding skin is protected by petroleum jelly.
Cantharidin (or sometimes cantharidin with salicylic acid) is applied precisely to the lesion of concern.
After the liquid dries the skin is covered with a dressing.
The dressing is removed after 4-6 hours.
The skin is then washed with soap and water.
A blister is expected to form over the next 24 hours.
You may be asked to pop the blister to drain the fluid for comfort but you should leave the roof of the blister intact.
Over the next few days, the skin overlying the blister will dry and peel, along with the lesion being treated.
After 1 week the skin should be healed.
Repeat treatment may be required in 1-2 weeks if some of the lesion remains or new lesions appear elsewhere.

What are the complications and side effects of Cantharidin treatment?

Lack of clearance of lesion (may take another course of treatment)
Mild discomfort (blister is not painful but can be a bit uncomfortable depending on body part)
Ring wart (can occur with any wart treatment)
Infection (very rare)
Pigmentary changes (especially in darker skin types)

This article was prepared by Dr Tevi Wain