Vancomycin Flushing Syndrome Mimicking an Allergic Reaction in a Severely Obese Patient: A Case Report of Vancomycin-Induced Hypersensitivity.

Vancomycin is a widely used antibiotic, particularly for the treatment of resistant infections like methicillin-resistant Staphylococcus aureus (MRSA). While generally safe, vancomycin is associated with adverse reactions, most notably vancomycin flushing syndrome (VFS). VFS, a non-IgE-mediated histamine release, is often misdiagnosed as an allergic reaction, especially when presenting with symptoms such as pruritus, erythematous rash, and flushing. This case report discusses a 71-year-old female who initially presented with symptoms suggestive of an allergic reaction to vancomycin but was later diagnosed with VFS after a more thorough assessment. The patient with a BMI of 62.5, diagnosed with sepsis secondary to HAP caused by MRSA, developed an erythematous rash, dizziness, warmth, and pruritus two minutes after the initiation of vancomycin infusion at the rate of 17mg/min. Initially suspected to be an allergic reaction, the infusion was halted, and antihistamines were considered, however not given. Upon further evaluation, the diagnosis was revised to VFS. This case emphasizes the importance of differentiating between VFS and true allergic reactions in patients receiving vancomycin. Early recognition and prompt cessation of the infusion are critical in preventing further complications. Clinicians should consider VFS in patients with rapid-onset symptoms during vancomycin infusion.