In this episode, we discuss the misunderstood side of our antibiotic hero, Vancomycin

Time Stamps

  • 0:28 Where did vancomycin come from, and why is it so controversial?
  • 4:37 What is vancomycin-induced nephrotoxicity and how common is it?
  • 7:28 Vancomycin trough monitoring – what is it good for?
  • 7:53 AUC to MIC ratio – the real math behind vancomycin dosing
  • 10:27 Review of teaching points

Show Notes

  • Initial formulations of vancomycin were only 70% pure, giving it its original muddy brown color.  Side effects seen included cytopenias, “red man syndrome”, and nephrotoxicity. With better technology, vancomycin is now 95% pure, and as a result has fewer side effects.
  • Vancomycin nephrotoxicity is defined by the IDSA as an increase in creatinine of 0.5mg/dL or by more than 50%, whichever is bigger.
  • Vancomycin causes nephrotoxicity through two mechanisms: acute interstitial nephritis (an allergic reactions) or renal tubular damage from oxidative stress.
  • Rates of nephrotoxicity appear to be low, although the exact number is difficult to determine. Most studies are retrospective or observational, and the few RCTs available may be subject to confounding.
  • Risk factors for nephrotoxicity include concomitant use of aminoglycosides or piperacillin/tazobactam, rates at or above 4g per day, duration of therapy, and critical illness, among others.
  • Vancomycin peaks do NOT correlate with toxicity or efficacy. Instead, this depends on the AUC/MIC ratio.
  • The AUC (area under the curve) represents the amount of drug the bacteria see over a 24 hour period. The MIC (minimum inhibitory concentration) represents how resistant the bacteria are to that antibiotic.
  • The AUC/MIC ratio is the best measurement of vancomycin’s effectiveness. The current rationale for checking vancomycin troughs is as a cheap, practical, but suboptimal surrogate marker for the AUC/MIC.

References

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