Healing Kitchen

"Beetle Juice" Wart Treatment Revived

What the Study Showed
How It Was Done
Why It's Important

What the Study Showed

An ancient medicine long used for wart removal gets a thorough re-examination in a 2001 article in the Archives of Dermatology. Researchers from New York University's School of Medicine analyzed numerous studies on the uses and effects of cantharidin, a substance derived from the blister beetle that has been used medicinally for more than 2000 years in China. The article takes a comprehensive look at cantharidin's origins, folk uses, current FDA status, dermatologic uses, and toxic effects..

In the 1950s, U.S. dermatologists used cantharidin to treat warts, but the substance lost its FDA approval in 1962 when new manufacturing regulations went into effect. Now, with a 1997 amendment to the Food, Drug, and Cosmetics Act, cantharidin has been nominated for the FDA's Bulk Substances List, which allows physicians to administer drugs compounded with cantharidin and other ingredients. The FDA has stated that while the list is under review, it would take no action against drugs made from these substances as long as they pose no significant safety risks.

The studies reviewed by the researchers generally found that cantharidin has an excellent safety record when applied to the skin by a physician to treat common warts or the soft growths called molluscum. Side effects are extremely rare, and such treatments produce no scarring. Complications including inflammation of lymph vessels may be somewhat more likely when cantharidin is used to treat plantar warts on the feet, but this was noted only in a very small study of just two patients.

The blister beetle is also known as the Spanish fly, and its "beetle juice" has long been infamous (but actually ineffective) as a purported aphrodisiac. Interestingly, when taken orally, cantharidin is poisonous--and can even be fatal. Because of the risk of accidental ingestion by children, or of severe blistering if applied to the skin incorrectly, cantharidin should only be applied in a physician's office. There have been no reports of cantharidin poisoning resulting from normal dermatological use, the study authors say.

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: 05/31/2002
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