D2.258 - Fixed drug eruption caused by co-amoxiclav

BACKGRAOUND: Fixed drug rash (FMO) is a type of skin allergic reaction caused by the drug, which is characterized by the recurrence of skin changes always in the same place after re-exposure to the drug. Clinically, the lesions appear anywhere on the body as single lesionsor multiple well-circumscribed hyperpigmented erythematous papules or plaques with itching,typically within 30 minutes to 8 hours of drug administration. Vesicles and bullae may form.The drugs most often associated with FMO are antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen and antiepileptics.

CASE REPORT: a 14-year-old girl was admitted due to suspected medication rash. It is known from the anamnestic that the patient has, after three occasions, during oral administration co-amoxiclav antibiotic therapy for the purpose of treating a breast abscess developed an erythematous rash andswelling in the area of ​​both elbows, both knees and the gluteal region after 10, 5 and 2 days from the start of the therapy. The drug was discontinued, and the symptoms subsided with local application corticosteroid therapy. Skin prick test, an intradermal test with co-amoxiclav and then epicutaneous test on predilection sites with co-amoxiclav, phenoxymethylpenicillin and cefpodoxime which were negative. After the accompanying parent gave consent, an oral challenge test with a gradual increase in the dose of co-amoxiclav in 45-minute intervals was performed. Five hours after a cumulative dose of co-amoxiclav of 875/125 mg, an erythematous rash developed with swelling on both elbows, which confirmed the diagnosis of FMO. In order to exclude the possible cross-reaction to other beta-lactam antibiotics, six weeks later, oral challenge test with phenoxymethylpenicillin and cefpodoxime were performed and came back negative. Considering the possible correlation between HSV infection and FMO, serological tests were performed and arrived negative.

CONCLUSION: From this case report, it is evident that negative skin allergy tests alone are notsufficient to rule out the diagnosis of FMO, and it is necessary to perform an oral provocation test.There are a few reported cases of FMO on amoxicillin. To our knowledge, this isthe third reported case of FMO on co-amoxiclav, and the first in the pediatric population with good resultstolerance to other beta-lactam antibiotics.