Test ID: VANRA    
Vancomycin, Random, Serum

Monitoring adequacy of drug concentration during vancomycin therapy whenever a specimen is submitted or collected without collection timing information

Vancomycin is an antibiotic used to treat infections caused by gram-positive organisms that are resistant to beta-lactam antibiotics, such as methicillin-resistant staphylococci (MRSA), Streptococcus viridans group, penicillin/cephalosporin-resistant Streptococcus pneumoniae, and penicillin/ampicillin-resistant Enterococcus species. The oral formulation, which is not absorbed, is used in the treatment of pseudomembranous colitis caused by Clostridium difficile. Vancomycin is also used when patients are intolerant or allergic to beta-lactam antibiotics.

Vancomycin has been associated with nephrotoxicity and ototoxicity, although it appears that many of these reports reflected impurities in early formulations. Monitoring of vancomycin-related nephrotoxicity is recommended only for patients with reduced renal function, those receiving aggressive or prolonged vancomycin regimens, or those at high risk including patients comedicated with other nephrotoxic agents.

Trough concentrations are recommended for therapeutic monitoring of vancomycin, preferably acquired at steady state (just before fourth dose). To avoid development of resistance, vancomycin trough levels should remain above 10.0 mcg/mL. Complicated infections require higher target levels, typically 15.0 to 20.0 mcg/mL. Peak concentrations do not correlate well to efficacy or nephrotoxicity, but may be useful for pharmacokinetic studies or for select patients.

Random levels may be ordered when attempting to determine when to dose vancomycin in patients with renal impairment or those undergoing dialysis.

VANCOMYCIN, TROUGH

Therapeutic: 10.0-20.0 mcg/mL

VANCOMYCIN, PEAK

Therapeutic: 20.0-45.0 mcg/mL

Trough levels correlate better with efficacy than peak levels, with target trough levels of 10.0 and 20.0 mcg/mL, depending on the type of infection.

Peak levels are not recommended for monitoring, except in select circumstances such as when performing pharmacokinetic analyses (eg, area under the curve: AUC determinations). Typical peak levels are between 20.0 and 45.0 mcg/mL.

These levels are consistent with Mayo Clinic Antimicrobial Therapy Guidelines.

As with any assay employing mouse antibodies, the possibility exists for interference by human antimouse antibodies (HAMA) in the sample, which could cause falsely lowered results.

Unspecific binding of heterophilic antibodies from the sample to glucose-6-phosphate dehydrogenase of the reagent may lead to falsely lower test results in very rare cases (<10[-6]).

1. Rybak M, Lomaestro B, Rotschafer JC, et al: Therapeutic drug monitoring of vancomycin in adult patients: A consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm. 2009;66:82-98

2. Estes L, Wilson J: Mayo Clinic Antimicrobial Therapy Quick Guide. Mayo Clinic. 2005. Updated July 29, 2020