Cantharidin in Dermatology

Cantharidin is natural toxin produced by the blistering beetle. It has both vesicant and keratolytic features by inducing acanthloysis through targeting the desmosomal dense plaque, leading to detachment of the desmosomes from the tonofilaments. There are two available liquid preparations for dermatologic use, Canthacur (0.7% cantharidin) and Canthacur PS (1% cantharidin 30%/salicylic acid/2% podophylotoxin). The former preparation is indicated for the treatment of common warts, periungual warts, and molluscum contagiosum, while the more potent latter preparation is indicated only for plantar warts. Both preparations provide painless applications with outcomes similar to other treatment modalities for warts and molluscum contagiosum; however, neither is approved by the Food and Drug Administration (FDA). The lack of FDA approval could be related to its toxic effects following oral ingestion, which include ulceration of the gastrointestinal and genitourinary tracts, along with electrolyte and renal function disturbance in humans and animals. The mechanism of action, dermatologic indications, application techniques, and complications of cantharidin preparations are discussed.