Vancomycin

Vancomycin is a frontline weapon against MRSA — but give it wrong, and you create the very resistance you're trying to fight. Knowing when and how to use it is non-negotiable.

Vancomycin is a glycopeptide antibiotic that kills gram-positive bacteria by inhibiting cell wall synthesis — it binds to the D-alanyl-D-alanine terminus of peptidoglycan precursors, preventing cross-linking. This mechanism makes it the drug of choice for serious MRSA infections (bacteremia, endocarditis, osteomyelitis, pneumonia) and for treating Clostridioides difficile colitis when given orally. IV vancomycin treats systemic infections because it is not absorbed from the GI tract. Oral vancomycin stays in the gut, which is exactly why it works for C. diff — it reaches the site of infection directly. Standard IV infusion runs over at least 60 minutes (often longer for doses above 1 g) to prevent infusion-related reactions. Dosing is weight-based, and trough levels guide therapy — the target AUC/MIC approach or trough of 15–20 mcg/mL for serious infections ensures adequate bactericidal activity while limiting harm. Troughs are drawn 30 minutes before the fourth or fifth dose at steady state.

Key Distinctions

Oral vancomycin treats C. diff only — it does NOT treat systemic infections because it isn't absorbed. IV vancomycin treats systemic MRSA infections but does not achieve adequate gut lumen concentrations for standard C. diff treatment (IV vancomycin may be added as adjunctive therapy in fulminant C. diff). Students commonly confuse the route-indication pairing and select IV vancomycin for C. diff, which is incorrect for non-fulminant disease. Don't confuse vancomycin (cell wall synthesis inhibitor, gram-positive only) with aminoglycosides (protein synthesis inhibitors, gram-negative coverage).

Clinical Pearl

Mouth for the gut, vein for the body. Oral vancomycin stays local for C. diff; IV vancomycin goes systemic for MRSA. Wrong route = wrong infection.

Adverse Effects

Vancomycin's major adverse effects are Red Man Syndrome (RMS), nephrotoxicity, and ototoxicity. RMS is a histamine-mediated reaction — not a true allergy — triggered by infusing too fast. It presents as flushing, erythema of the face/neck/upper torso, pruritus, and sometimes hypotension. The intervention is to pause the infusion, notify the provider, and expect orders to restart at a slower rate with diphenhydramine premedication. Standard infusion time is at least 60 minutes per 1 g; faster rates dramatically increase RMS risk. Nephrotoxicity risk increases when vancomycin is combined with other nephrotoxic agents such as aminoglycosides, NSAIDs, or IV contrast. Monitor serum creatinine and BUN at baseline and throughout therapy. Trough levels are drawn 30 minutes before the next dose; the target trough range is typically 15–20 mcg/mL for serious infections, though levels above 20 mcg/mL sharply raise nephrotoxicity risk. Ototoxicity manifests as tinnitus, hearing loss, or vertigo and may be irreversible. Report any auditory complaints immediately. Adequate hydration is essential to protect the kidneys throughout therapy.

Key Distinctions

Don't confuse RMS with anaphylaxis — RMS lacks urticaria/wheals, bronchospasm, and angioedema; it's rate-related, not immune-mediated. Students often mix up vancomycin trough timing (30 minutes before the dose) with aminoglycoside peak timing (30–60 minutes after). Ototoxicity from vancomycin can be permanent, unlike many drug-induced GI side effects that resolve after discontinuation.

Clinical Pearl

Red Man = Rate Man. Slow the drip, and the red goes away. True allergy gets worse no matter the rate — that's the distinction that saves you on test day.