[Fixed drug eruption to clarithromycin: The importance of challenge tests in diagnosis]

Determining the substance responsible for recurrent fixed drug eruption (FDE) may be difficult in the case of patients on multiple medication. Allergy testing may prove invaluable in such situations, as we demonstrate herein with an original case.

A 49-year-old man presented a rash on the seventh day of treatment with esomeprazole, clarithromycin and amoxicillin prescribed for gastritis involving Helicobacter pylori. The condition regressed spontaneously within a few days, but left three areas of hyperpigmentation. The patient subsequently reported four further episodes consisting of stereotypical reactivation in the areas of the three initial lesions and occurring 24hours after use of clarithromycin (2 episodes) and amoxicillin (2 episodes). The patient resumed proton pump inhibitor therapy (esomeprazole) without incident. Based on history taking, an initial diagnosis was made of multiple fixed drug eruption involving amoxicillin and clarithromycin. The initial skin allergy investigations were negative (patch-tests for amoxicillin and clarithromycin on healthy skin on the patient's back and on the affected area). After discussion, we decided to reintroduce the suspected drugs in succession. Beginning with clarithromycin, 12h after a single dose of 250mg, we noted an erythematous reaction on the pigmented areas, together with a burning sensation. In an identical challenge test with amoxicillin (500mg), the latter drug was perfectly well tolerated, ruling out the diagnosis of FDE to amoxicillin and thus the diagnosis of multiple FDE suggested by the patient history.

FDEs to macrolides are rare, and herein we report a new case. Our observation confirms the diagnostic value of challenge tests in FDE. These tests should only be performed in the event of non-severe FDE, in other words not in bullous or systemic reactions, and they often constitute the only diagnostic approach possible, since skin tests are rarely positive during investigation for FDE.