A 60-year-old patient receiving vancomycin for MRSA bacteremia develops sudden flushing, erythema, and pruritus over the face and upper trunk during infusion. The most likely mechanism is:

• A IgE-mediated type I hypersensitivity reaction
• B Complement activation via the alternative pathway
• C Cytokine release from activated T lymphocytes
• D Direct non-immunologic mast cell degranulation ✓

Explanation

The 'Red Man Syndrome' caused by rapid vancomycin infusion is due to direct, non-immunologic stimulation of mast cell degranulation, resulting in histamine release. It is not an IgE-mediated allergy and can be prevented by slowing the infusion rate over at least 60 minutes or by pretreatment with antihistamines. This distinguishes it from true anaphylaxis.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.