Fixed drug eruption caused by pamabrom

Erythema Multiforme Secondary to Dimenhydrinate in a Patient With Previous Similar Reactions to Pamabrom

Objective: To report a case of erythema multiforme secondary to dimenhydrinate and pamabrom cross-sensitivity. Case Summary: A 22-year-old Chinese female presented with a complaint of lip mucosal ulceration with necrosis and stomatitis, worsening over the past 24 hours and associated with reduced oral intake and incomplete opening of the mouth. Presentation was accompanied by a generalized rash and genital mucosal involvement. The only new systemically ingested agent was dimenhydrinate approximately 4 days prior to admission. She had no significant medical history, but was labeled to be allergic to acetaminophen. She had a positive history of 2 similar presentations secondary to Panadol Menstrual (acetaminophen and pamabrom), once 3 years ago and again 5 months prior to the current admission. An objective causality assessment revealed that the adverse drug event was “probable” to dimenhydrinate. A detailed history revealed a negative drug challenge to acetaminophen. She had previously taken plain acetaminophen and Beserol (acetaminophen and chlormezanone) with no reaction. Discussion: A comprehensive history taking facilitated the diagnosis of erythema multiforme secondary to dimenhydrinate without the need to perform invasive testing, and the removal of erroneous allergy labeling to acetaminophen. Dimenhydrinate and pamabron both contain theophylline-related structures in their chemical composition. Similar reactions to pamabrom strongly suggested cross-sensitivity to theophylline-related structures. Conclusions: To our knowledge, this is the first report of erythema multiforme due to dimenhydrinate with pamabron cross-sensitivity. We recommend that comprehensive medication-history taking be carried out for all drug-allergy patients to ensure greater informed decision making when choosing medications to use for that patient in the future.