Imiquimod not linked to paraben sensitivity

Skin & Allergy News,  Jan, 2007  by John R. Bell

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BALTIMORE -- Imiquimod treatment does not appear to be associated with increased sensitivity to weak allergens, such as parabens, according to preliminary study findings, reported Dr. Jennifer Chwalek at a meeting on contact dermatitis.

The North American Contact Dermatitis Croup has estimated the rate of sensitivity to paraben mix to be 1.7% in a group of roughly 4,000 tested patients, she noted. But the risk is increased in people with compromised skin, with some studies reporting a prevalence of up to 8% in such persons, said Dr. Chwalek of the University of Maryland, Baltimore.

Imiquimod does contain two parabens: methylparaben and propylparaben. The most common side effect with imiquimod is erythema. Given that imiquimod is an immune adjuvant, Dr. Chwalek and colleagues intend to identify any reactions associated with imiquimod use in their study cohort. Patients were recruited from outpatient clinics at the Baltimore VA Medical Center and have a history of imiquimod use. Exclusion criteria included concurrent high-dose oral corticosteroid use.

The investigators have been patch-testing patients for six substances: all four parabens (methyl, ethyl, propyl, and butyl), as well as Keri and Eucerin brand skin lotions. A control group is tested on petrolatum, and patients are assessed at 48 hours.

To achieve an 80% power to detect increased imiquimod sensitivity, the investigators determined that 140 patients would be needed, based on the reported prevalence of 1%-4% for paraben sensitivity in the literature.

So far, Dr. Chwalek and colleagues have tested 18 patients (15 of whom are men), ranging in age from 31 to 84 years. In this group, imiquimod was used to treat 12 actinic keratoses, four basal cell carcinomas, and three warts, with an average of 24 applications per patient. The most common side effects in this group were redness (13 patients), crusting (10), pruritus (8), bleeding (6), pain (5), and edema (4). One patient developed fever, chills, arthralgias, and decreased appetite after taking imiquimod for basal cell carcinoma.

Of these 18 patients, 3 patients tested positive for reaction to imiquimod, 3 had a weak positive reaction, and the remaining 13 were negative. No patients were positive for sensitivity to the drug vehicle, and one was positive for sensitivity to paraben mix.

Although further study is needed to confirm these results, the investigators have observed thus far that imiquimod use does not seem to increase risk of sensitivity to parabens, Dr. Chwalek said at the meeting, which was sponsored by the Experimental Contact Dermatitis Research Group and the American Contact Dermatitis Society.

Paraben, which is colorless, odorless, and inexpensive, is one of the most common preservatives used in cosmetics, Dr. Chwalek said, noting that the average person is exposed to approximately 70 mg of parabens each day.

JOHN R. BELL

Associate Editor

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