Cantharidin 0.7%

Route: In-office topical application by or under the direct supervision of a licensed prescriber to individual lesions only.

• Applied with a wooden applicator or fine brush precisely to each lesion; avoid application to surrounding normal skin.
• Allow to air-dry for 1–2 minutes before covering; occlusion with adhesive tape for 2–6 hours is common for molluscum contagiosum.
• Patients are instructed to wash the treated area with soap and water after the prescribed contact time (typically 2–6 hours).
• Do not dispense cantharidin solution to patients for self-administration; in-office application by the prescriber or trained clinician is required.

Cantharidin 0.7% is applied in small, precise quantities to individual lesions. There is no set milligram dose per se—the quantity applied is determined by lesion size and number:

• Apply to each lesion individually; do not treat large areas simultaneously.
• In molluscum contagiosum: typically covered with tape for 4–6 hours before washing off.
• In warts: contact time varies by protocol; prescriber determines optimal time based on lesion characteristics.
• Treatment may be repeated every 2–4 weeks depending on clinical response.

Cantharidin: The precise mechanism in molluscum contagiosum is not fully established. Current evidence suggests cantharidin activates endogenous serine proteases in epidermal keratinocytes, disrupting intercellular desmosomes and the junctions that maintain keratinocyte adhesion. This produces acantholysis (separation of epidermal cells) and formation of a blister at the dermal-epidermal junction or within the epidermis. In molluscum contagiosum, the resulting blistering and inflammation promote shedding of virus-infected epidermal cells and may stimulate the immune response to facilitate viral clearance. In warts, physical destruction of the hyperkeratotic, HPV-infected tissue is the primary mechanism.

Cantharidin 0.7% (Ycanth®) received FDA approval in July 2023 as the first FDA-approved topical treatment for molluscum contagiosum, validating its clinical utility. It is also widely used for common warts. This compounded formulation is prepared for patient-specific use by the prescriber. Application is in-office only; it should not be dispensed to patients for home use.

Prescriber monitoring:

• Instruct patients on washing timing; failure to wash at the appropriate time can result in excessive blistering and scarring.
• Avoid application near eyes, mucous membranes, and intertriginous areas.
• Assess for secondary infection in blistered areas at follow-up.
• Monitor for autoinoculation of molluscum lesions during the post-treatment blister phase.

Contraindications:

• Application near eyes or mucous membranes
• Application to anogenital area in children
• Known hypersensitivity to cantharidin
• Not for patient self-administration

Warnings & Precautions:

• Cantharidin is a vesicant; if applied to normal skin or contact occurs with normal mucous membranes, blistering and severe local reactions can occur.
• Systemic absorption of cantharidin can cause severe toxicity including renal, gastrointestinal, and genitourinary damage; do not use on large areas or damaged/broken skin.
• Blistering is an expected local response; patients must be counseled to report signs of secondary infection.
• Pediatric use: standard of care for molluscum contagiosum in children; follow strict application protocols.

Drug Interactions:

• No clinically significant drug interactions identified for topical application at this concentration.

Common Side Effects: Blister formation at the application site (expected), erythema, burning or tingling, secondary blistering beyond the treated lesion if spread occurs; healing is typically complete within 1–2 weeks after blister resolution.

Store at controlled room temperature (20–25°C / 68–77°F). Protect from light; brown/amber container recommended. Do not refrigerate or freeze. Keep container tightly sealed. Store in a secure location out of reach of children and unauthorized personnel. Use before the beyond-use date assigned by Genesis Compounding.

What is cantharidin and how does it treat molluscum and warts?

Cantharidin is a compound from the blister beetle that activates enzymes (serine proteases) inside skin cells, causing them to separate and form a blister. In molluscum contagiosum, this blistering destroys the infected skin cells and triggers an immune response to clear the virus. In warts, it physically destroys the infected hyperkeratotic tissue.

Is cantharidin FDA-approved?

Yes—cantharidin 0.7% (Ycanth®) was FDA-approved in July 2023 for molluscum contagiosum. This compounded preparation is a 503A prescription preparation from Genesis Compounding for a specific patient. Prescribers who compound for individual patients must ensure they are meeting all applicable legal and clinical standards.

Will there be a blister after treatment?

Yes. Blistering is the expected and intended response. The blister typically develops within 24–48 hours of application. Patients should wash the area after the prescribed contact time and follow prescriber instructions for wound care. Contact your prescriber if signs of infection develop.

Why can't I apply this at home?

Cantharidin is a potent vesicant that can cause severe chemical burns and blistering if misapplied to normal skin or mucous membranes. In-office application by the prescriber ensures precise placement on lesions only, minimizing risk to surrounding tissue.

How many treatments will I need?

Most lesions require one to three treatment sessions, spaced 2–4 weeks apart. The number of treatments depends on the number, size, and location of lesions and individual clinical response as assessed by your prescriber.