The coapplication of two topical creams, one containing 6% sodium nitrite and another containing 9% citric acid, together producing nitric oxide, was effective in treating genital warts in close to one-third of patients, in a study published online April 29 in JAMA Dermatology.

In a randomized, placebo-controlled trial, 31% of patients treated with the nitric oxide topical treatment had complete clinical clearance within 12 weeks, compared to 14% of those assigned to placebo (P = .01), Dr. Anthony D. Ormerod of the University of Aberdeen, Scotland, and associates reported (JAMA Derm. 2015 April 29 [doi:10.1001/jamadermatol.2015.0381]).

Researchers randomized 299 patients (64% men) from 40 treatment centers across Europe to one of three dose regimens of sodium nitrite and citric acid, or placebo. Sodium nitrite reacts with citric acid to produce nitric oxide, which acts as an antiviral and antimicrobial; for the study, patients applied two separately prepared creams, allowing the agents to combine at the treatment site. Only the highest-dose combination studied, sodium nitrite 6% and citric acid 9% applied twice daily, was shown to be significantly more effective than placebo.

Patients receiving the highest dose also saw the highest rate of adverse effects in the study: Of the 73 patients in that arm, 92% reported treatment site adverse events, including itching, pain, edema and skin staining. “This study proves the concept that acidified nitrite is effective in treating anogenital warts and has identified the dose required for efficacy,” Dr. Ormerod and associates wrote. “For the sensitive anogenital application site, this dose probably represents the optimal one for further evaluation. For future research, extending the duration of treatment might improve the efficacy,” they said.

The researchers noted that studies of another agent used to treat genital warts, imiquimod, demonstrated clearance rates of between 37% and 52%.

The study was funded by the pharmaceutical manufacturer ProStrakan, with additional support from Origin Pharmaceuticals. Dr. Ormerod reported honoraria and royalties from ProStrakan and disclosed patents filed on acidified nitrite for treatment of skin infections. Four other co-authors reported support from ProStrakan.