Clinical Review

Implications of Vancomycin Troughs Drawn Earlier Than Current Guidelines

Health care providers were not consistently adherent to the 2009 Infectious Diseases Society of America guidelines regarding the proper timing of testing of trough serum concentration levels.

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References

Vancomycin was isolated in the 1950s, but due to impurities causing adverse events and semisynthetic penicillin production, its use was greatly reduced. 1,2 However, this medication gained in popularity 30 years later as a first-line treatment for methicillin-resistant Staphylococcus aureus infections.

In 2009 the Infectious Diseases Society of America (IDSA), American Society of Health System Pharmacists, and Society of Infectious Diseases Pharmacists developed a consensus review of the therapeutic monitoring and dosing of vancomycin in adult patients. 3 Trough serum concentration levels are recommended as the most accurate and convenient method to monitor vancomycin. Per IDSA guidelines, an optimal trough is intended to be high enough to clear infections (> 10 mg/L) and prevent the development of vancomycin intermediate and resistant bacteria. Troughs should be obtained just before the next dose in steady-state conditions (starting just before the fourth dose) in patients with normal renal function.

Since the development of these guidelines, vancomycin trough levels are often drawn early. 4-7 This may lead to an overestimation of the true trough concentration. A study by Morrison and colleagues in Boston, Massachusetts, found that 41.3% of vancomycin troughs were drawn early, and this resulted in statistically significant increases in the vancomycin concentrations, the rate of vancomycin regimen adjustments (decrease, discontinuation, or holding of dose), and the repeat vancomycin level orders compared with correctly timed troughs. 5 It was noted by the study authors that lowering the daily dose of vancomycin based on early trough levels could lead to an underdosing of vancomycin and an increase in intermediate or resistant bacteria.

Related: IDWEEK: Antibiotic ‘time-out’ cut vancomycin use

The prevalence and implications of early trough samples have been measured at only 1 facility, and it is unknown whether these data can be reproduced elsewhere. 5 Thus, this study sought to determine the prevalence and corresponding clinical actions of early trough levels at the Captain James A. Lovell Federal Health Care Center (JALFHCC). This is a unique facility that in 2010 combined a VA hospital with a DoD hospital. This facility cares for 67,000 military and retiree beneficiaries each year from southwestern Wisconsin and northwestern Illinois.The primary objective of this study was to measure the rate of early troughs drawn and their resultant effect on vancomycin regimens compared with correctly timed troughs. Secondarily, this study sought to compare the rate of repeated vancomycin trough levels in early vs correctly timed measurements.

Methods

This retrospective cohort analysis compared the outcomes of early and correctly timed vancomycin troughs. This study was approved by the Edward Hines, Jr. VA Hospital and JALFHCC Institutional Review Board. Veteran patients aged ≥ 18 years, hospitalized at JALFHCC, and receiving IV vancomycin at dosing intervals of 8, 12, 24, and 48 hours with measured trough levels between July 1, 2009, and July 1, 2013, were included in this study. Patients were excluded from analysis if vancomycin was given at any schedule other than the previously stated frequencies, they received hemodialysis during the treatment period, or their insurance coverage was through TRICARE (these patients had either active-duty or retired active-duty status).

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