Cantharidin

Cantharidin is a naturally occurring odorless, colorless fatty substance of the terpenoid class that is produced as an oral fluid in the alimentary canal of the male blister beetle. For its natural purpose, the male blister beetle secretes and presents the cantharidin to a female beetle as a copulatory gift during mating. Post-copulation, the female beetle places the cantharidin over her eggs as protection against any potential predators.

Topical cantharidin products do not necessarily demonstrate any particular better effectiveness at treating topical skin conditions like warts than other commonly available vesicant and/or keratolytics although various studies have also investigated the possibility of using cantharidin as an inflammatory model or in cancer treatment. Regardless, the ongoing lack of FDA approval is likely related to certain toxic effects that were observed following oral ingestion, which include ulceration of the gastrointestinal and genitourinary tracts, along with electrolyte and renal function disturbance in humans and animals .

Available synthetically since the 1950s, topical applications of cantharidin have been used predominantly as a treatment for cutaneous warts since that time. In 1962 however, marketers of cantharidin failed to produce sufficient efficacy data, resulting in the FDA revision of approval of cantharidin. Nevertheless, it gained its first FDA approval on Jul 21, 2023, under the brand name YCANTH™ by Verrica Pharmaceuticals for the treatment of molluscum contagiosum in adult and pediatric patients. The approval was based on positive results from 2 phase III trials, CAMP-1 and CAMP-2, where 46% and 52% of patients treated with cantharidin achieved complete molluscum clearance, respectively.

Cantharidin is approved by the FDA for the topical treatment of molluscum contagiosum in adult and pediatric patients 2 years of age and older. It has also been approved by Health Canada for the treatment of common warts (verruca vulgaris), periungual warts, and molluscum contagiosum as a standalone product and resistant and heavily keratinized plantar warts as a combination product with salicylic acid and podophyllin.

At the same time, such topical cantharidin applications have also been used for a number of off-label indications like callus removal, cutaneous leishmaniasis, herpes zoster, and acquired perforating dermatosis. Furthermore, since most topical cantharidin applications are most commonly available in a 0.7% formulation or a more potent 1% mixture, the 0.7% formulation is most commonly indicated for the treatment of common warts, periungual warts, and molluscum contagiosum while the more potent 1% mixture is typically limited only for use by healthcare professionals in a clinical setting for treating plantar warts and other more specialized off-label conditions.

Moreover, there have also been studies into whether or not cantharidin could be effective at being used as an inflammatory model or in cancer treatment - either of which has yet to elucidate any results formally.