vancomycin in serum/plasma

Indications

• therapeutic drug monitoring, vancomycin therapy

Reference interval

• large patient variability in vancomycin pharmacokinetics; patients with renal impairment should be closely monitored
• published therapeutic levels for most patients are as follows:
  • PEAK CONCENTRATION: no higher than 30-40 ug/mL
  • TROUGH CONCENTRATION: no higher than 5-10 ug/mL
• a target trough concentration of 15-20 ug/mL should be considered for pediatric patients with serious infections

* note vancomycin resistance: MIC > 2 ug/mL

Principle

The VANC pack is used in the DuPont ACA discrete clinical analyzer to quantitatively measure vancomycin, an antibiotic, in serum & plasma. It is an adaptation of Syva's homogeneous enzyme immunoassay technique, EMIT. The reagents used in this methodology are matched lots of vancomycin monoclonal antibody & vancomycin-glucose-6-phosphate dehydrogenase conjugate. The concentration of vancomycin determines the amount of vancomycin - glucose-6-phosphate dehydrogenase (VANC-G6PD) conjugate that is bound to the vancomycin monoclonal antibody. The unbound conjugate catalyzes the oxidation of glucose-6-phosphate, with the simultaneous reduction of NAD to NADH, more rapidly than does the bound conjugate. The rate of increasing absorbance at 340 nm due to the increase in NADH is related to the concentration of vancomycin by means of a calibration curve or a mathematical function.

Clinical significance

Vancomycin is an antibiotic derived from the organism Nocardia orientalis. It is a tricyclic glycopeptide with a molecular weight of 1449 Daltons. It is usually dispensed as vancomycin hydrochloride, either in solution or as a water soluble white powder. Vancomycin is active against most gram positive bacteria: streptococci, corynebacteria, clostridia, Listeria, & bacillus species. It is especially important in the treatment of infections due to methicillin- & cephalosporin-resistant organisms. It is bactericidal against most of the susceptible bacteria, but with some, notably enterococci, it is bacteriostatic. Vancomycin plus an aminoglycoside may act synergistically against many of these organisms. It has only limited activity against gram negative bacteria. Vancomycin was discovered more than 25 years ago, but it has been used sparingly because of toxicity & high cost. Current usage is generally limited to those infections in which other antibiotics are ineffective or contraindicated.

Vancomycin serum levels may be overestimated if measured by fluorescence polarization immunoassay or radioimmunoassay due to interference by vancomycin metabolites. The EMIT method does not suffer this disadvantage.

Specimen

Patient preparation: No special patient preparation is required.

Collect blood samples by venipuncture following established good laboratory practices. If the sample is obtained through the infusion set, flush the line thoroughly with saline before taking the blood sample. With some exceptions, any anticoagulant may be used to collect plasma for analysis. Serum, as well as plasma, may be used for most assays. If is very important that the physician be informed of the times of sample collection & dose administration; this information should be supplied to the laboratory with each sample & reported with the results of each test. Samples derived from blood should be refrigerated upon collection & stored frozen (-20 degrees Celsius or colder) if not analyzed within 24 hours. Complete mixing of each thawed sample is required before analysis.

More general terms

• vancomycinin body fluid
• therapeutic drug measurement

More specific terms

• vancomycin free in serum/plasma
• vancomycin in serum/plasma peak
• vancomycin in serum/plasma post dialysis
• vancomycin in serum/plasma random
• vancomycin in serum/plasma trough