Plasma level monitoring of vancomycin is necessary due to the drug's biexponential distribution, intermediate hydrophilicity, and potential for ototoxicity and nephrotoxicity, especially in populations with poor renal function and/or increased propensity to bacterial infection. Vancomycin activity is considered to be time-dependent; that is, antimicrobial activity depends on the duration that the serum drug concentration exceeds the minimum inhibitory concentration of the target organism. Thus, peak serum levels have not been shown to correlate with efficacy or toxicity; indeed, concentration monitoring is unnecessary in most cases. Circumstances in which therapeutic drug monitoring is warranted include: patients receiving concomitant aminoglycoside therapy, patients with (potentially) altered pharmacokinetic parameters, patients on haemodialysis, patients administered high-dose or prolonged treatment, and patients with impaired renal function. In such cases, trough concentrations are measured.
Vancomycin is an antibiotic used to treat a number of bacterial infections .  It is recommended intravenously as a treatment for complicated skin infections , bloodstream infections , endocarditis , bone and joint infections, and meningitis caused by methicillin-resistant Staphylococcus aureus .  Blood levels may be measured to determine the correct dose.  Vancomycin is also recommended by mouth as a treatment for severe Clostridium difficile colitis .  When taken by mouth it is very poorly absorbed.