Thursday, November 01, 2007

October case posted: The evidence behind vancomycin dosing

The October 2007 issue of the JMLA is up in PubMed Central, including the October case study, "Approaching and analyzing a large literature on vancomycin monitoring and pharmacokinetics."

An excerpt from the case:

At morning rounds in your hospital's intensive care unit, a resident from the team presents a 55-year-old woman (weight 129 lbs) with a past medical history of multiple sclerosis, cerebellopontine angle meningioma, hypothyroidism, and a neurogenic bladder requiring a Foley catheter. This patient was transferred from her nursing home 3 days ago with a fever and altered mental status. Results from the nursing home bacterial culture of the patient's urine revealed Gram negative rods. Bacterial culture of blood drawn from her peripheral intravenous (IV) line at the nursing home indicated Gram positive cocci. Blood cultures redrawn upon hospital admission are still pending and require confirmation.

According to the patient's chart, she began empiric treatment at the nursing home with vancomycin (1,000 milligrams [mg] intravenously every 12 hours) and piperacillin-tazobactam (3.375 g IV every 6 hours) for urosepsis 4 days ago. The patient's current serum creatinine is 0.56 micrograms per deciliter (mg/dL) (normal range: 0.6–1.1 mg/dL) [1], and her estimated creatinine clearance is 104 milliliters per minute (mL/ min) (normal range: 88–128 mL/min) [2]. Her current body temperature is 97.2° Fahrenheit. Today is day 4 of this patient's vancomycin and piperacillin-tazobactam regimen and hospital day 3.

In reviewing the plan for the next twenty-four hours, the attending physician notes that the patient currently has a standing order for a laboratory test of the vancomycin trough level in her serum, with the blood sample to be taken just prior to the next dose of the drug. On day three of antibiotic therapy, the patient's serum vancomycin trough level was eleven mcg/mL, and, on day four, the trough was eighteen mcg/mL. The institution's target range for the serum trough level of vancomycin is five to twenty mcg/mL.

The attending physician initiates a discussion with the team—including a fellow, three residents, a pharmacist, a dietitian, the unit's nurses, and you, as the team's librarian—about monitoring of vancomycin. The clinician queries the team about the rationale for the standing order for vancomycin trough monitoring. The residents indicate that they often order this lab test when a patient is receiving vancomycin in an attempt to ensure therapeutic effectiveness and to prevent adverse effects of the drug but are not aware of any documentation behind the practice. The pharmacist comments that clinical practice can sometimes evolve before supporting evidence exists and that standards of practice at a hospital may not always be supported by evidence from the literature. In response to this discussion, the group asks you to identify any evidence supporting or disproving the practice of routine monitoring of trough levels in patients being treated with vancomycin in the adult critical care setting. Figures 1 and 2 provide elaboration from the team's attending physician and pharmacist on the significance of this question to clinical practice on the unit.
Additional discussion to follow soon!

Reference:Lee P, DiPersio D, Jerome RN, Wheeler AP. Approaching and analyzing a large literature on vancomycin monitoring and pharmacokinetics. J Med Libr Assoc. 2007 October; 95(4): 374–380.

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