How It Was Done
The researchers reviewed 49 studies and articles on the uses and effects of cantharidin, which is found in the body fluids of more than 1500 species of blister beetles. Two species are commonly found in the southern and southwestern United States.
Cantharidin kills warts by creating a blister on the growth, which causes it to detach from the surrounding skin. Cantharidin products are formulated with substances that create an oily, or colloidal, film. First, the physician pares or "shaves" the wart, then applies the drug to the wart and a very narrow circle of surrounding skin. The area is sealed with nonporous tape, which is removed after four hours. Within 24 to 48 hours a blister will form, and healing is normally complete within four to seven days. Occasionally, resistant warts will require a second treatment.
In a very small number of patients involved in the studies (1 of 100 participants in one, and 3 of 61 in another), a ring of small satellite warts surrounding the original wart appeared after cantharidin treatment. The authors note, however, that this complication is just as likely to occur with any other type of wart removal therapy.
Why It's Important
Although cantharidin was used successfully for many years for wart removal, and satisfied all existing safety requirements, manufacturers of cantharidin products failed to submit data required by a 1962 amendment to the Food, Drug, and Cosmetic Act. It was therefore lost as a treatment for warts for 40 years. Now, by adding it to the nominated Bulk Substances List, the FDA is on the verge of making this ancient medicine available again. Because it is a safe and effective treatment for warts and molluscum, cantharidin after its FDA approval can now be re-added to dermatologists' treatment options. In particular, cantharidin is valuable for wart removal because no cases of scarring have ever been reported when it was properly applied by a physician. Scarring is possible with other well-known wart destruction methods, such as freezing (cryotherapy) or electrical burning (cautery).
Source: Moed L, Shwayder TA, Chang MW. Cantharidin revisited: a blistering defense of an ancient medicine. Arch Dermatol 2001 Oct;137(10):1357-60
Date Published: 6/1/2002
Date Reviewed: 11/2/2005