Seventy-six digital and periungual
warts in 40 patients were treated topically with
cantharidin, a potent blistering agent. The material, dissolved in equal parts of
acetone and
collodion, was applied directly to the
warts. Occlusion facilitated blistering. No pretreatment was required. The
warts were re-treated at weekly intervals until clinically cured.Fifty-six per cent of digital
warts and 33 per cent of periungual
warts cleared after a single application of
cantharidin. Few required more than three treatments. Observation was continued for more than six months in more than half of the cases. Cure was lasting in about 70 per cent of the cases in which the long term result was known.
Cantharidin ranks with liquid
nitrogen in effectiveness, but it is painless to apply and does not cause
scarring. For these reasons it is especially useful in children.The main disadvantage is
pain and tenderness at the treated site for two to four days in some patients. This can be avoided by careful application of the
drug. Occasionally new
warts appear at the edge of the
cantharidin blister. They are best treated by
curettage and desiccation.