Snapshot A 45-year-old man presents to the emergency room for right lower extremity cellulitis. He reports feeling feverish and malaise for the past 2 days and noticed redness and swelling along his right leg. He reports having tripped a few days ago, sustaining a cut on his foot. He denies any recent surgeries or long trips. He has a history of methicillin-resistant Staphylococcus infections. A Doppler is negative for blood clot. On physical exam, he is febrile. He is started on broad-spectrum antibiotics. He requests an anti-histamine prior to infusions, as he has previously had a flushing reaction to this particular antibiotic in the past. (Cellulitis) Introduction Drugs vancomycin Mechanism of action binds to D-Ala-D-Ala, a cell wall precursor, and prevents peptidoglycan formation mainly bactericidal but bacteriostatic against Clostridium difficile Mechanism of resistance not susceptible to beta-lactamases D-Ala-D-Ala mutation to D-Ala-D-Lac, preventing vancomycin from binding Clinical use gram-positive rods and cocci especially methicillin-resistant Staphylococcus aureus (MRSA) ampicillin-resistant Enterococcus Clostridium difficile (oral dose) often reserved for serious infections Adverse effects ROTN Red man syndrome pretreat with antihistamines and slow infusion rate vancomycin directly causes degranulation of mast cells and histamine release characterized by a pruritic, erythematous rash of the face, neck, and upper trunk within minutes to days of vancomycin exposure Ototoxicity Thrombophlebitis Nephrotoxicity must be renally dosed in patients with renal impairment DRESS syndrome Drug Reaction with Eosinophilia and Systemic Symptoms