A case of possible anaphylaxis to ASA and structurally unrelated NSAIDs.

Background: Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most commonly used classes of medications, and are among the leading causes of drug hypersensitivity. NSAIDs hypersensitivity reactions are classified by symptom involvement and NSAIDs subclass cross-reactivity. Reactions varying from cutaneous involvement to respiratory symptoms can be triggered by multiple NSAIDs subclasses. Anaphylaxis, while rare, can be induced by a single NSAID, with tolerability of other structurally unrelated subclasses. Reactions that fall outside of these traditional categories are deemed "blended reactions". We report a unique case of possible anaphylaxis to acetylsalicylic acid (ASA) and ibuprofen, two structurally dissimilar NSAIDs, indicating a severe blended reaction outside of the typical NSAIDs hypersensitivity reaction categories.

Case presentation: An otherwise healthy 45 year old woman was referred to the Allergy and Immunology clinic after developing acute onset dyspnea, lip swelling, and generalized urticaria with ibuprofen use requiring treatment with intramuscular epinephrine in the emergency department. She previously tolerated ibuprofen, naproxen, and acetaminophen and had no history of urticaria, angioedema, asthma, or nasal polyps. She underwent an oral challenge to ASA whereby she developed urticaria and throat irritation with rebound symptoms requiring 2 doses of intramuscular epinephrine. On subsequent visits she passed treatment dose acetaminophen and celecoxib challenges. She was counseled to avoid all other NSAIDs and ASA desensitization was offered should this medication be clinically indicated in the future.

Conclusions: NSAIDs hypersensitivity reactions can be triggered by individual NSAIDs with tolerance of other subclasses or by multiple structurally unrelated NSAIDs due to COX-1 inhibition. Determining the type of reaction (NERD, NECD, NIUA, SNIUAA, or SNIDHR) allows for appropriate oral challenges and safe alternative therapy recommendations. However, not all clinical reactions fit perfectly into these categories. Patients may also develop blended reactions. Our case highlights a severe blended reaction to multiple unrelated NSAIDs, including likely anaphylaxis to ASA. We note the utility of drug provocation tests (DPTs) to identify safe alternative medication options, as well as the importance of performing DPTs in settings properly equipped to assess and manage severe hypersensitivity reactions including anaphylaxis.