Vancomycin

When a vancomycin dose is given, its concentration in the blood first rises, reaches a peak level and then falls gradually. The next dose is timed to overlap the falling level so that a minimum concentration is always maintained in the blood. Measurement of blood levels is usually requested at times that reflect the lowest concentration (trough) and the highest concentration (peak) to evaluate the effectiveness of therapy. Trough levels are collected just prior to a patient’s next vancomycin dose. Peak levels are collected 1 to 2 hours after the end of the intravenous vancomycin dose. These results are then used to determine the appropriate amount of drug and the appropriate timing between doses to ensure that the blood concentration remains in the therapeutic range.

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

Vancomycin should be measured on the second day of treatment, immediately before the next dose, and subsequent doses should be adjusted according to the vancomycin concentration. Some doctors will request trough levels every few days throughout vancomycin treatment. Some will request both trough and peak concentrations at regular intervals. Others do not feel that general monitoring is necessary and will only request the tests on patients who are at increased risk of kidney damage because of other medicine that they are taking or poor kidney function. They may also use the test on those who are not responding to treatment as expected. In pregnant women, there is a risk of toxic effects affecting the foetus. The drug is only used in pregnancy if the potential benefits outweigh the risks, and vancomycin concentration measurements are essential in this situation to reduce the risk of foetal toxicity.

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 lower 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 and upper body and a significant drop in blood pressure. Discontinuing the infusion results in resolution of the clinical features.

Kidney function tests such as urea, creatinine and creatinine clearance may be requested prior to the start of vancomycin therapy and at intervals, or as needed, to evaluate changes in kidney status.

The more widely an antibiotic is used, the more bacteria develop resistance to it. The medical community tries to be conservative in its use of vancomycin, reserving it for patients with severe illness and few other treatment options in order to reduce the emergence of vancomycin-resistant bacteria. In recent years, some resistant and intermediate (decreased sensitivity) strains of Staphylococcus aureus and strains of Enterococcus have emerged and antibiotic resistance is becoming an increasing problem in controlling serious infections.