Anterior ST-Segment Elevation Myocardial Infarction Shortly After Cefaclor Exposure: A Case Report Highlighting Kounis Syndrome as a Differential Diagnosis.

BACKGROUND Kounis syndrome is an acute coronary syndrome associated with allergic or hypersensitivity reactions, but establishment of causality is difficult when objective allergy-related tests are unavailable during emergency treatment. This report describes anterior ST-segment elevation myocardial infarction (STEMI) occurring shortly after cefaclor exposure and highlights the diagnostic limitations of attributing the event to hypersensitivity in routine emergency clinical practice. CASE REPORT A 61-year-old man with a history of positive penicillin skin testing, but no prior penicillin administration, developed severe chest pain approximately 1 hour after self-administration of oral cefaclor for respiratory symptoms. He had no rash, urticaria, wheezing, angioedema, oropharyngeal edema, hypotension, or dyspnea; no prehospital antihistamines, corticosteroids, or epinephrine were administered. Electrocardiography showed ST-segment elevation in V2 to V6, and emergency coronary angiography demonstrated 90% proximal left anterior descending artery stenosis with Thrombolysis in Myocardial Infarction grade II flow. Primary percutaneous coronary intervention restored grade III flow and relieved symptoms. High-sensitivity cardiac troponin I increased from 0.57 to 1.10 ng/mL and peaked at 3.92 ng/mL at 15 hours. Serum tryptase, histamine, total and specific IgE, and intracoronary imaging were not obtained. The Naranjo score was 2, indicating a possible adverse drug reaction. CONCLUSIONS The temporal association prompted consideration of Kounis syndrome, but severe fixed coronary stenosis makes coincidental plaque-related STEMI a major alternative diagnosis. Early allergy biomarker sampling and careful causal assessment are important in similar cases.