Fixed drug eruption with ornidazole having cross‐sensitivity to secnidazole but not to other nitro‐imidazole compounds: a case report

Abstract

Fixed drug eruption (FDE) is characterized by single or multiple skin lesions which occur at the same site each time the drug is administered [1]. Lesions are usually round or oval and well defined, however their number and severity may increase after each exposure. Swelling and redness of skin are typically seen within 30 min to 8 h after exposure. Lesions are more commonly seen on extremities, genitals and perianal areas but they may appear on any location. Persistent hyperpigmentation at the site of the lesion is normally seen after healing. Accompanying systemic symptoms are mild with FDE. Cross-sensitivity may occur with structurally similar drugs. The offending drug is thought to function as a hapten that preferentially binds to basal keratinocytes, thereby releasing lymphokines and antibodies thus damaging the basal cell layer [2]. Nitroimidazoles are low molecular weight antimicrobial compounds with excellent activity against anaerobic micro-organisms and protozoa. They are the first line drugs for hepatic and intestinal amoebiasis. All the nitroimidazoles: metronidazole, tinidazole, ornidazole, secnidazole and satranidazole, have a similar nitroimidazole ring but different side chains. Although all these molecules have been used for a long time without many side-effects, only metronidazole and tinidazole have been reported to cause FDEs with cross sensitivity to each other [3, 4] and are included in the list of drugs causing FDE. We report a case of FDE caused by ornidazole which showed cross-sensitivity to secnidazole but not to metronidazole, tinidazole or satranidazole.