Cantharidin is a medication that has been used by dermatologists as a treatment for molluscum contagiosum and warts since the 1950s. Following topical application, cantharidin is absorbed by the fat layers of the skin. Topical cantharidin treatment causes formation of blisters within 24 to 48 hours. Healing is complete in 4 to 7 days without scarring.
In a retrospective study at the Department of Dermatology, Henry Ford Hospital, Detroit, of 300 children with molluscum contagiosum treated with cantharidin, 90% of the patients experienced resolution of symptoms and an additional 8% noted some improvement.
Warts are treated more intensively. “Warts are pared, followed by cantharidin application to the wart and a 1-mm rim of normal skin, and occluded with nonporous tape. Cantharidin is washed off in 4 hours. If necessary, paring and retreatment are done in 1 to 2 weeks, with contact time increased if needed.”
A high cure rate has been achieved following treatment of plantar warts with a topical formulation consisting of 1% cantharidin, 5% podophyllotoxin and 30% salicylic acid (CPS). A study compared the efficacy of topical CPS and cryotherapy (freezing) and concluded that topical CPS is more effective than cryotherapy in the treatment of plantar warts.
Because of cantharidin's potential for toxicity, the FDA has proposed that cantharidin should be limited to "topical use in the professional office setting only." Severe blistering can result from improper use, and ingestion, especially by children, can be fatal. Treatment of mucous membranes is contraindicated and placement of cantharidin near the eyes and eyelids should be avoided to prevent scleral erosion.
When cantharidin is used appropriately, complications are exceedingly rare. Mild to moderate pain, temporary erythema, a transient burning sensation, and pruritis may occur. There is no scarring with proper use.
Cantharidin lost FDA approval in 1962 because its manufacturers failed to submit data attesting to cantharidin's efficacy. Although not commercially available, cantharidin is approved for compounding on a customized basis for individual patients.