Liam Walsh, B.Sc.(Pharm), RPh

Vancomycin – One size doesn’t fit all

Vancomycin is a glycopeptide type antibiotic used to treat a wide variety of infections. It is a bactericidal antibiotic that functions mainly by disrupting cell-wall synthesis in gram positive organisms.

Vancomycin is especially useful when treating patients with documented or suspected infections caused by gram positive bacteria resistant to other therapies, such as Methicillin Resistant Staphylococcus aureus (MRSA) or Enterococcus faecium.

Unfortunately for clinicians, while very useful, vancomycin is a drug with a narrow therapeutic window. A number of toxicities can occur when vancomycin exceeds certain levels in the blood (nephrotoxicity, ototoxicity, etc.) or when the drug is infused too quickly (“red man syndrome”). To avoid these toxicities, while maintaining adequate therapeutic levels of the drug, individualized dosing and close monitoring of drug levels are crucial.

Traditional dosing of 1g q12h may not be suitable for all, or even most, patients. For most adults, an initial dose of 15-20mg/kg of Actual Body Weight(ABW) is sufficient. For patients who are severely ill, and adequate levels must be obtained sooner, a loading dose of 25-30mg/kg ABW may be considered. The interval at which the dose is given can be obtained with the following table:

Where ClCr can be estimated with the following equation:

If patient is obese (>130% of ideal body weight), Adjusted body weight (IBW –+0.4(Actual BW-IBW) should be used.

Trough levels should be drawn immediately prior to the 3^rd dose or the 4^th day of therapy, whichever is sooner. Target vancomycin trough levels vary depending on indication (usually fall in the 10-20mg/L range.

For assistance with vancomycin dosing, monitoring, or dosing adjustments, a pharmacist is available for consult at the following times :Monday to Friday 0700-2200, Weekends and Holidays 0700-1800, All other times an on-call pharmacist may be reached through Locating.

Consults may be entered in I3 as “Consult Clinical Pharmacy: Pharmacist for Therapeutic Drug Monitoring” as well.

Please see: “Vancomycin Empiric Adult Dosing Guideline”, available via skyline for more detail.

Reference:

Rybak M, Lomaestro B, Rotschafer J et al. Therapeutic monitoring of vancomycin in adult patients: A consensus review of the American Society of Health-System Pharmacists, the Infectious Disease Society of America, and the Society of Infectious Disease Pharmacists. Am J Health-Syst Pharm. 2009; 66:82-98