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Understanding vancomycin levels

Rosini, Jamie M. PharmD, BCPS; Srivastava, Nicole PharmD, BCPS

doi: 10.1097/01.NURSE.0000435209.34142.0e
Department: PATIENT SAFETY
Free

Jamie M. Rosini is a clinical pharmacy specialist in emergency medicine and Nicole Srivastava is a clinical pharmacy specialist in infectious diseases at Christiana Care Health System in Newark, Del.

The authors have disclosed that they have no financial relationships related to this article.

VANCOMYCIN LEVELS are used to optimize dosing to help prevent bacterial resistance, improve patient outcomes, and avoid drug toxicity. A glycopeptide antibiotic, vancomycin is routinely used for treating infections caused by Gram-positive bacteria, including Streptococcus and Enterococcus species and Staphylococcus aureus.1 It's used empirically to treat meningitis, endocarditis, bacteremia, pneumonia, and skin and skin structure infections.2 This article describes vancomycin levels and their utility in clinical practice.

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What are vancomycin levels?

Vancomycin serum trough concentrations, levels drawn just before the next scheduled dose, are considered the most practical method for monitoring efficacy when the pathogen is susceptible.2 Vancomycin peak concentrations, levels from blood specimens obtained 30 to 60 minutes after drug administration, aren't routinely monitored in clinical practice.

Random vancomycin serum levels are obtained at any point after a dose is given. The timing of subsequent doses is then prescribed based on the random level result—in other words, the drug is dosed by level. This dosing strategy is often used in patients with severe renal impairment or on hemodialysis.3

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Why are vancomycin levels important?

Studies have shown that when serum vancomycin levels are maintained above 10 mcg/mL, the emergence of vancomycin intermediate-resistant S. aureus and vancomycin-resistant S. aureus are less likely to develop.2 Consensus guidelines recommend a target trough concentration of 15 to 20 mcg/mL for clinical success in severe infections.2 To reach these targets, weight-based doses of vancomycin (15 to 20 mg/kg) should be prescribed.

Studies have suggested that higher doses and higher trough concentrations are associated with increased rates of nephrotoxicity.4 To monitor for toxicity, levels should be performed in patients who are receiving aggressive dosing, are prescribed concurrent nephrotoxic drugs, have fluctuating renal function, or require a prolonged course of treatment. Trough level monitoring to prevent ototoxicity isn't indicated because the incidence is rare and doesn't correlate with levels.2

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When are blood specimens for vancomycin levels obtained?

Specimens for vancomycin trough concentrations should be obtained just prior to (that is, 30 minutes before) the fourth dose (including the loading dose, if given) or at steady state.2 At five half-lives, about 97% of steady-state serum concentrations will be reached. In adults with normal renal function, the half-life of vancomycin is 6 to 12 hours.2 If steady state occurs within five half-lives (that is, in 30 to 60 hours), a vancomycin trough before the fourth dose is acceptable in a patient receiving every 8- or 12-hour dosing.

In some situations, blood specimens for a vancomycin trough level should be obtained earlier. For example, if a patient is prescribed once-daily dosing of vancomycin, waiting until the fourth dose may not be ideal.

For patients receiving intermittent hemodialysis, one of two approaches to monitoring vancomycin serum concentrations can be used.3

  • Predialysis level: Obtain a blood specimen for a random vancomycin level before dialysis. Hemodialysis using high-flux filters can remove about 30% of vancomycin.3 For serious infections, clinicians should consider redosing postdialysis if the random predialysis level is less than 25 mcg/mL.
  • Postdialysis level: Obtain a blood specimen for a random level about 2 to 4 hours postdialysis. Levels may be falsely low and serum concentrations can rebound after dialysis. In other words, levels based on blood specimens obtained immediately postdialysis may overestimate dialytic clearance of vancomycin. For serious infections, clinicians should consider redosing postdialysis if the random level based on a blood specimen obtained 2 to 4 hours postdialysis is less than 20 mcg/mL.5

Clinicians should consider repeating vancomycin trough levels once weekly if a patient is on a stable regimen or if a patient's renal function changes.2

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How are vancomycin levels interpreted?

Vancomycin levels must be interpreted in conjunction with appropriately timed blood specimens and previously scheduled doses. Waiting for a trough level result before administering a scheduled dose is cautioned against because this will interrupt the dosing schedule and potentially allow prolonged subtherapeutic levels. Following institution-specific policy is recommended.

Here are some questions to ask when interpreting a vancomycin level:

  • Was the blood specimen obtained at the appropriate time (30 minutes before the fourth dose)?
  • Were any doses before the blood level missed or administered early or late?

Nurses should be aware of the following when interpreting a vancomycin level:

  • Obtaining the blood specimen for the vancomycin level from the I.V. line used for vancomycin administration will give falsely elevated levels.
  • Missed doses may result in unintentionally low levels.
  • Variable administration times may result in misleading levels.

Therapeutic drug monitoring of vancomycin is a complex process that involves an understanding of the usefulness of levels as well as careful interpretation by nurses, pharmacists, and prescribers.

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REFERENCES

1. Vancomycin hydrochloride for injection [package insert]. Hospira, Lake Forest, IL; 2012. http://www.hospira.com/Images/EN-2972_32–91157_1.pdf.
2. Rybak M, Lomaestro B, Rotschafer JC, et al. Therapeutic monitoring of vancomycin in adult patients: a consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm. 2009;66(1):82–98.
3. Vandecasteele SJ, De Vriese AS. Vancomycin dosing in patients on intermittent hemodialysis. Semin Dial. 2011;24(1):50–55.
4. Lodise TP, Lomaestro B, Graves J, Drusano GL. Larger vancomycin doses (at least four grams per day) are associated with an increased incidence of nephrotoxicity. Antimicrob Agents Chemother. 2008;52(4):1330–1336.
5. Launay-Vacher V, Izzedine H, Mercadal L, Deray G. Clinical review: use of vancomycin in haemodialysis patients. Crit Care. 2002;6(4):313–316.
© 2013 by Wolters Kluwer Health | Lippincott Williams & Wilkins.