Recurrent fixed drug eruption due to metronidazole elicited by patch test with tinidazole Contact Dermatitis 2005: 53: 169–170 A. Prieto, M. De Barrio, S. Infante, A. Torres, M. Rubio and S. Olalde Department of Allergology, Hospital General Universitario Gregorio Maran ˜o ´n, Madrid, Spain Key words: cross-reactivity; fixed drug eruption; metronidazole; nitroimidazole; positive lesional patch test; tinidazole. Among the few cases of fixed drug eruption (FDE) due to metronida- zole to have been reported (1–7), patch testing has demonstrated to be useful in diagnosis (5–7). Case Report A 34-year-old woman, with a per- sonal history of FDE due to sulphon- amides, had been treated 4 months ago with oral metronidazole for tri- chomonal vaginitis. On the 4th day of treatment, she developed pruritic erythematous and blistered lesions on interdigital areas and on the pal- mar side of the thumb finger of her left hand. About 3 months later, the same lesions appeared in the same locations some hours after the topical application of the first ovule of metro- nidazole for recurrent vaginitis, remaining as hyperpigmented macules at these locations. FDE due to metro- nidazole was diagnosed clinically. Patch testing with tinidazole and ornidazole 10% in dimethyl sulfoxide (DMSO) was performed on normal skin and on residual lesions. Tinidazole applied on a residual lesion was positive (Fig. 1), though negative on normal skin, while ornidazole was negative on both. The patient declined any further testing. Discussion Metronidazole is a drug belonging to the 5-nitroimidazole group. There are few cases reported of FDE due to metronidazole (1–7). Most of them have been diagnosed by oral challenge testing (2–4), but topical provocation testing has been docu- mented as useful and safe for diag- nosis when applied on residual lesions (5–7). Various drug concen- trations and vehicles [metronidazole 0.8% gel (5), 5% and 10% aq (6) and 50% pet (7)] have been used. Cross-reactivity among nitroimida- zoles has been reported by positive oral challenge testing: mainly between metronidazole and tinidazole (2, 8, 9) and, in one case, between albendazole and metronidazole (10). Such authors found no cross-reactivity with secni- dazole (2) or with albendazole, keto- conazole and mebendazole (8). Gastaminza et al. (7) reported a case of FDE due to metronidazole confirmed by a positive patch test applied on a residual lesion (metro- nidazole 50% pet.). They also investi- gated cross-reactivity by patch testing on residual lesions and on normal skin with tinidazole (50% pet.) and tioconazole (Trosid 1 cream as it), with negative results. We describe a case of recurrent FDE following metronidazole therapy, with cross-reactivity with tinidazole confirmed by positive residual- lesional patch testing, using DMSO as vehicle. As has been reported with other drugs (11,12), patch testing can be useful in the study of cross- reactivity among nitroimidazoles. References 1. Walfish A E, Sapadin A N. Fixed drug eruption due to doxycycline and metronidazole. Cutis 2002: 69: 207–208. 2. Thami G P, Kanwar A J. Fixed drug eruption due to metronidazole and tini- dazole without cross-sensitivity to secni- dazole. Dermatology 1998: 196: 368. 3. Shelley W B, Shelley E D. Fixed drug eruption due to metronidazole. Cutis 1987: 39: 393–394. 4. Naik R P, Singh G. Fixed drug eruption due to metronidazole. Dermatologica 1977: 155: 59–60. 5. Short K A, Fuller L C, Salisbury J R. Fixed drug eruption following metro- nidazole therapy and the use of topical provocation testing in diagnosis. Clin Exp Dermatol 2002: 27: 464–466. 6. Vila J B, Bernier M A, Gutierrez J V, Gomez M T, Polo A M, Harrison J M, Miranda-Romero A, Munoz C M. Fixed drug eruption caused by Fig. 1. CONTACT POINTS CONTACT DERMATITIS 2005: 53: 169–182 * COPYRIGHT # BLACKWELL MUNKSGAARD 2005 * ALL RIGHTS RESERVED * CONTRIBUTIONS TO THIS SECTION WILL NOT UNDERGO PEER REVIEW, BUT WILL BE REVIEWED BY THE EDITOR *