VAIL, COLO. — Many providers have begun to treat molluscum contagiosum with cantharidin, a blistering agent produced by a beetle, instead of with liquid nitrogen.
The reason is that cantharidin is less painful and very well tolerated compared with curettage or liquid nitrogen, Dr. Lawrence F. Eichenfield said at a meeting sponsored by the American Academy of Pediatrics.
“It has been shown in a variety of studies [to be] a highly effective agent,” said Dr. Eichenfield, a pediatric dermatologist at the University of California, San Diego, and Rady Children's Hospital, also in San Diego. The majority of the time, he said, one to three 4-hour applications are sufficient to treat the lesions.
Dr. Eichenfield uses the method made popular by a report in 2000 from investigators at Northwestern University, Chicago. In their report, the investigators treated 300 patients with cantharidin and later interviewed their parents. The researchers said that, with an average of about two treatments, 90% of the patients were cleared of their lesions. Another 8% had improvement but were not cleared by the treatment, although their lesions resolved afterward (J. Am. Acad. Dermatol. 2000;43:503–7).
Ninety-two percent of the patients experienced blistering, and 37% reported erythema at the site after treatment, which lasted for up to 3 weeks. Fourteen percent reported mild to moderate pain after treatment and 10% reported a transient burning sensation. Other adverse events—including pruritus (6%) and bleeding (1%)—occurred less frequently. There were no serious events.
Ninety-five percent of parents said they would have their child treated the same way again. Of the 14 who would not, 3 gave their child's blistering as the reason and 1 mentioned pain. The others found multiple visits inconvenient or did not give a reason.
In the Northwestern method used by Dr. Eichenfield, the cantharidin (0.7% concentration) is daubed on the lesions with the wooden end of a cotton-swab, sparing the surrounding skin. He treats no more than 20 lesions at a time; he does not treat facial lesions with this method.
The sites are not occluded afterward, and the agent is washed off with soap and water 4–6 hours later, Dr. Eichenfield said.
Although the treatment is relatively safe, he said he would recommend physicians receive training before using cantharidin to avoid severe blisters.
Cantharidin is less painful and very well tolerated compared with curettage or liquid nitrogen. DR. EICHENFIELD