When a vancomycin dose is given, its concentration rises in the blood, peaks, and then falls. The next dose is timed to be given in anticipation of the falling level. The goal is to overlap the doses enough so that a minimum concentration is always maintained in the blood. Measurement of blood levels are ordered at times to reflect the lowest concentration (trough) and the highest concentration (peak) to evaluate the adequacy of dosing and adequacy of clearance of the drug. Trough levels are collected just prior to a patient’s next vancomycin dose. Peak levels are collected 1 to 2 hours after the completion of the intravenous vancomycin dose. The trough and peak values are used by clinical pharmacists and doctors to calculate rates of absorption and clearance of the drug. These results are then used to determine the appropriate amount of drug and the appropriate timing between doses to assure that the blood concentration remains in the therapeutic range.

For additional information on how the test is used, see Therapeutic Drug Monitoring.

There is not a widespread consensus on the use of the vancomycin test. Some doctors will order trough levels every few days throughout vancomycin treatment. Some will order both trough and peak concentrations at regular intervals. Many do not feel that general monitoring is necessary and will only order the tests on patients who are at increased risk of nephrotoxicity (because of other medications, decreased kidney function, etc.) and on those who are not responding to treatment as expected.

If trough levels of vancomycin are above the minimum level, then the patient should be receiving enough of the drug to be effective. If the patient’s infection is not responding to the treatment, then the doctor may either continue the drug for a longer period of time or consider other treatment options. If peak concentrations are below maximum levels, then the patient is at less risk of developing nephrotoxicity and/or ototoxicity (but may still experience either complication). Peak concentrations may vary, depending on the consistency of collection timing and on changing drug clearance rates. If the peak concentration is excessive, the doctor may either alter the dose or alter the dosing schedule.

An intravenous vancomycin dose must be given slowly. Patients given the dose at a rapid rate are at an increased risk of developing “red man syndrome,” a histamine reaction that causes flushing of the face, a rash on the upper body, and a significant drop in blood pressure.

Kidney function tests such as BUN (Blood Urea Nitrogen) and creatinine and creatinine clearance may be ordered prior to the start of vancomycin therapy and at intervals, or as needed, to evaluate changes in kidney status.