Vancomycin

Mechanism

The legendary "drug of last resort" for serious gram-positive infections, especially MRSA. A large glycopeptide antibiotic that blocks bacterial cell wall construction by binding to the building blocks before they can be assembled. Given IV for bloodstream infections and oral for C. difficile colitis (where it stays in the gut). Has been saving lives since the 1950s.

Effects

ANTIMICROBIAL MECHANISM: Glycopeptide antibiotic produced by Amycolatopsis orientalis (originally Streptomyces orientalis). Binds with high affinity to the D-Ala-D-Ala terminus of pentapeptide precursors in peptidoglycan synthesis (lipid II), sterically blocking both transglycosylation (polymerization) and transpeptidation (crosslinking). This inhibits cell wall synthesis, leading to osmotic instability and cell death. Slowly bactericidal against most Gram-positives. Concentration-independent killing — AUC/MIC is the primary PK/PD driver. Minimal membrane or intracellular activity (unlike lipoglycopeptides). SPECTRUM: MRSA (MIC90 1 μg/mL — the reference standard), MSSA, CoNS (including methicillin-resistant), Streptococcus pyogenes, S. pneumoniae (including penicillin-resistant), viridans group strep, E. faecalis, E. faecium (vancomycin-susceptible), C. difficile (oral administration for CDI). No Gram-negative activity. No anaerobic coverage (except C. difficile). MIC BREAKPOINTS: CLSI/FDA: S. aureus susceptible ≤2 μg/mL. VISA 4-8 μg/mL. VRSA ≥16 μg/mL. Enterococcus susceptible ≤4 μg/mL. RESISTANCE MECHANISMS: VanA (most common acquired) — D-Ala-D-Lac modification, high-level resistance (MIC >256). Transferable between species (enterococci to S. aureus — VRSA). VanB — D-Ala-D-Lac, moderate-level resistance, inducible. Interestingly, teicoplanin retains activity against VanB. VISA — cell wall thickening with altered peptidoglycan cross-linking, trapping vancomycin in outer cell wall layers (MIC 4-8). hVISA — heteroresistant subpopulations within an otherwise susceptible strain (MIC 1-2 by standard testing but contains VISA subpopulations). Tolerance (slow killing without MIC change). MIC creep: debate about whether vancomycin MICs have increased over time — some surveillance data says yes, some says no. PHARMACOKINETICS: Vd ~0.4-1.0 L/kg. Half-life 4-6 hours (normal renal function). Renal elimination (~80-90% unchanged in urine). Protein binding ~55%. Poor CNS penetration (10-20% with inflamed meninges). Poor lung/ELF penetration (~25% of serum). Good bone penetration. Oral vancomycin is NOT absorbed systemically — stays in GI lumen (used for CDI). TOXICITY: NEPHROTOXICITY: Occurs in 5-25% with IV vancomycin. Vancomycin-associated AKI (VAKI). Mechanism debated — proximal tubular injury, possibly via oxidative stress and cast formation. Risk factors: concurrent nephrotoxins (especially piperacillin-tazobactam — significantly increases AKI risk), high troughs >20 μg/mL, prolonged therapy, ICU, obesity. OTOTOXICITY: Historically cited but evidence is weak for vancomycin alone. Risk increases with concurrent aminoglycosides. RED-MAN SYNDROME: Histamine release from mast cells and basophils. Flushing, pruritus, erythema of upper body. NOT a true allergy. Rate-dependent — occurs with rapid infusion (<1 hour). Slow infusion to ≥1 hour (2 hours for >1g) prevents it. Pretreat with antihistamine if needed. LINEAR IgA BULLOUS DERMATOSIS: Rare but specific to vancomycin — vesiculobullous rash. Requires drug discontinuation.

Practitioner Guide

CLINICAL PEARLS — INFECTIOUS DISEASE SPECIALIST PERSPECTIVE: DOSING REVOLUTION (2020 Guidelines): The 2020 ASHP/IDSA/SIDP vancomycin therapeutic monitoring guideline fundamentally changed vancomycin dosing. KEY CHANGE: Target is now AUC/MIC 400-600 (assuming MIC 1), NOT trough 15-20 μg/mL. Bayesian AUC-guided dosing: use PK software (e.g., PrecisePK, DoseMeRx, InsightRx, Bayesian VTDM) to estimate AUC from 1-2 levels. If Bayesian software unavailable: use two-level approach (peak drawn 1-2h post-infusion + trough pre-dose) to calculate AUC by trapezoidal method. If only trough available (fallback): target trough 15-20 μg/mL remains reasonable for serious infections, but AUC-guided dosing is preferred. LOADING DOSE: 25-30 mg/kg (ABW, capped at 3g) for serious infections. This achieves therapeutic levels faster. Standard maintenance: 15-20 mg/kg (ABW) q8-12h, adjusted by AUC/levels. OBESITY: Use ABW for loading dose (cap 3g). For maintenance, some guidelines use adjusted BW. Obese patients often need q8h dosing. Vd increases with obesity. THE PIPERACILLIN-TAZOBACTAM INTERACTION: Concurrent pip-tazo significantly increases vancomycin-associated AKI (OR ~3-4x, multiple meta-analyses). Mechanism debated (cast formation, direct tubular injury). Clinical implication: if using vancomycin + beta-lactam for empiric Gram-positive + Gram-negative coverage, prefer cefepime or meropenem as the Gram-negative agent over pip-tazo. ORAL VANCOMYCIN: For CDI only. 125 mg PO q6h x 10 days (mild-moderate, though fidaxomicin is now preferred first-line). Severe CDI: 500 mg PO q6h + metronidazole 500 mg IV q8h ± vancomycin retention enemas. Oral vancomycin is NOT absorbed — stays in GI lumen. Can be given via NG tube, or as retention enema for ileus. CONTINUOUS INFUSION: Used in some ICUs (especially Europe). Loading dose then 30-40 mg/kg/day as continuous infusion. Target steady-state concentration 20-25 μg/mL. Advantages: less peak-related toxicity, simpler monitoring (any time = steady state), potentially less AKI. Disadvantages: requires dedicated IV line, more drug used per day. WHEN VANCOMYCIN IS SUBOPTIMAL: MIC ≥2 μg/mL — AUC/MIC 400-600 is difficult to achieve without toxic doses. Switch to daptomycin, TMP-SMX, linezolid, or lipoglycopeptide. Pneumonia — poor ELF penetration. Consider linezolid (superior lung levels, PMID: 22895573) or telavancin. MONITORING: AUC-guided: draw levels per Bayesian protocol. Traditional: trough before 4th dose (steady state). SCr at baseline, then q48-72h (daily in ICU). CBC weekly (for rare neutropenia with prolonged courses). Audiometry only if concurrent aminoglycosides or >2 weeks therapy.

Evidence

• Effect of Vancomycin or Daptomycin With vs Without an Antistaphylococcal β-Lactam on Mortality, Bacteremia, Relapse, or Treatment Failure in Patients With MRSA Bacteremia: A Randomized Clinical Trial.

  Tong SYC et al. (2020) — JAMA — PMID: 32044943

  In 352 adults with MRSA bacteremia, adding an antistaphylococcal beta-lactam to standard therapy (vancomycin or daptomycin) did not significantly improve the 90-day composite endpoint, reduced persistent bacteremia at day 5, and increased acute kidney injury.

  strong

Research Summary

TIER 1 (Gold Standard): Rybak et al., 2020 — ASHP/IDSA/SIDP therapeutic monitoring guideline: AUC/MIC 400-600 replaces trough-based monitoring (AJHP, PMID: 32191793 — landmark practice-changing guideline). Wunderink et al., 2012 (ZEPHyR) — linezolid vs. vancomycin for MRSA nosocomial pneumonia: linezolid non-inferior with trend toward superiority (Clinical Infectious Diseases, PMID: 22895573). Liu et al., 2011 — IDSA MRSA treatment guidelines (Clinical Infectious Diseases, PMID: 21208910). FDA-approved 1958. Multiple meta-analyses of vancomycin nephrotoxicity, especially the pip-tazo interaction. CDC/IDSA CDI guidelines. TIER 2 (Strong): Moellering, 2006 — "Vancomycin: A 50-Year Reassessment" (Clinical Infectious Diseases — comprehensive historical review). Lodise et al., 2008 — AUC/MIC target derivation (Clinical Infectious Diseases). Kullar et al., 2011 — AUC-guided vs. trough-guided dosing outcomes. DrugBank DB00512. WHO Essential Medicines List. SENTRY/EARSS surveillance data. TIER 3 (Moderate): Decades of clinical experience from ID pharmacists and specialists. Institutional antibiograms tracking MIC trends. Bayesian dosing software validation studies. International dosing variations (continuous infusion more common in Europe/Australia). Conference presentations spanning 60+ years of vancomycin clinical use. KEY FINDINGS: (1) AUC-guided dosing is the new standard — reduces nephrotoxicity while maintaining efficacy. (2) The pip-tazo interaction is clinically significant and avoidable. (3) Vancomycin remains the backbone of MRSA therapy despite newer alternatives. (4) For pneumonia, vancomycin is suboptimal — consider linezolid or telavancin. (5) Oral vancomycin for CDI is being displaced by fidaxomicin as first-line. GAPS: Whether AUC-guided dosing truly reduces AKI vs. trough-based (RCT ongoing). Continuous infusion vs. intermittent (definitive RCT needed). Optimal duration for bacteremia (emerging 7-day vs. 14-day debate). ACTIVE TRIALS: Multiple ongoing for AUC-guided dosing outcomes, continuous infusion, duration optimization, and head-to-head comparisons with newer agents.