Vulvar allergic contact dermatitis to metronidazole

A non-atopic 58-year-old woman was referred to us for intense vulvar erythema with scattered oozing erosions, vulvovaginal itching and burning sensation accompanied by a cottage cheese-like vaginal discharge, progressively worsening. She was applying an ointment containing clotrimazole 20% and metronidazole 4% (Meclon, Alfasigma, Bologna, Italy) and occasionally with an ointment containing lidocaine 2% (Vagisil, Combe Italia s.r.l., Milan, Italy). Patient's history revealed recurrent vulvovaginal candidiasis self-treated on demand during the last months. The two topical products were stopped and genital lesions and symptoms promptly disappeared after treatment with mometasone furoate ointment (once daily for 10 days) and oral fluconazole (200 mg daily for 2 days). Six weeks after clinical resolution, the patient was patch-tested with the SIDAPA (Società Italiana Dermatologia Allergologica Professionale Ambientale) baseline series (SmartPractice, Rome, Italy) and the two topical products “as is”. Patch tests were applied on the back and left in occlusion for 2 days, using the Haye's Test Chambers (Haye's Service, Alphen aan den Rijn, The Netherlands) on Soffix tape (Artsana, Grandate, Italy). Readings were performed on day (D) 2, D4 and D7, and positive reactions at D4 and D7 to nickel sulfate (++), fragrance mix-I (++) and Meclon cream (++) were observed. Subsequently, patch tests with clotrimazole 5% pet. and metronidazole 1% pet. were performed, with positive reaction to metronidazole (++).