Plantar warts (aka plantar verrucas) are superficial skin lesions caused by the human papilloma virus (HPV). On the feet, they often look like a callus or corn and are found along the toes and bottoms of the feet. Depending on their size and location, they may, or may not be painful. If the wart is not tender, treatment is not always necessary, and the wart could resolve on its own over the course of several months. If painful, several treatment options are available.
Warts live on the outer layer of skin, making them difficult to treat. The body has a difficult time recognizing the virus, so treatment is often aimed at topical treatments that cause direct trauma to the wart. In a previous blog, I discussed ten different treatment options for warts. Of the ten mentioned, one of my favorites to use is Cantharidin.
Cantharidin, sometimes referred to as “Beetle Juice”, and often purchased as the product Catharone, is a beetle vesicant that has been used for medicinal purposes for over 2,000 years (1,2). For the specific purposing of treating plantar warts, it only dates back to the 1950s (1,2). When topically applied, cantharidin acts as a blistering agent, separating the viral epidermal skin tissue layer from the underlying, unaffected tissue layers.
In 1962, the FDA removed Cantharidin from the market because the manufacturers failed to submit efficacy data for the product (1,2). Fifteen years later, the FDA Modernization Act of 1997 was established to help reform “…the regulation of food, medical products, and cosmetics” (3). The FDA now routinely proposes substances to be included on the Bulk Substance List, which makes them eligible for compounding by pharmacists; however, according to this document, as of this month, it appears that Cantharidin continues to only be nominated (and not accepted) to that list.
The controversy of using Cantharidin is most likely related to the fatalities that have been reported with ingestion of it and not with the potential side effects associated with its topical application. Therefore, despite its regulations, physicians continue to use the product for topical applications in the treatment of plantar warts and molluscum contagiosum (another viral skin infection), likely because it can be used on children and is well-tolerated.
The Procedure: What to Expect
Treating warts with cantharidin (or Cantharone) is easily performed in a clinical setting, but should by done by a licensed healthcare professional. After the wart is debrided, the cantharidin liquid solution is applied to the warty tissue. As the solution dries, the area turns white. It is then temporarily covered with non-porous tape, which helps suffocate the virus. The procedure itself is not painful; however, over the course of the next 24 hours, a blister forms, which may become painful, especially if it is along the bottom of the foot. Within days, though, the blister should dry up, become a callus, and eventually fall off.
Follow-up appointments are made 2-3 weeks later, at which time the area is debrided of any non-viable callused tissue. If there is residual warty tissue found, another treatment of cantharidin can be performed.
DISCLAIMER: The above information is meant for educational purposes only and should not be construed as medical advice. Please consult the doctor, or your own healthcare professional, should you have questions or concerns related to your health.
1. Moed, L., Shwayder, T. A., & Chang, M. W. (2001). Cantharidin revisited: a blistering defense of an ancient medicine. Archives of dermatology, 137(10), 1357-1360.
2. Stapp, M.D. (2012). Use of Cantharidin for Verruca. Podiatry Institute, Chapter 4, PDF.
3. The FDA Modernization Act of 1997 (Nov 1997). Retrieved from https://www.fda.gov/RegulatoryInformation/LawsEnforcedbyFDA/SignificantAmendmentstotheFDCAct/FDAMA/ucm089179.htm.
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