HOW VANCOMYCIN IS USED IN AUSTRALASIA - A SURVEY

Background: Vancomycin serum concentrations have been monitored over the last 30 years in an attempt to avoid dose-dependent toxicity and enhance efficacy. Current literature recommendations for peak and trough concentrations are usually in the range of 20-40 mg/L and 5-10 mg/L, respectively. Literature recommendations regarding the time at which peak concentrations are measured are highly variable, ranging from immediately after the end of the infusion to three hours post-dose. Aims: To identify how vancomycin dosing is being monitored and assess variability in the current practice. Methods: A survey of microbiology departments and infectious disease physicians in major Australasian hospitals was undertaken. The variability in the current practice was assessed by fitting mean recommendations to a two compartment Bayesian model. Results: Of the 83 (70%) who replied 71 (86%) monitored vancomycin concentrations. Fifty-four percent targeted peak concentrations within the range of 20-40 mg/L, and 73% targeted trough concentrations less-than-or-equal-to 10 mg/L. The time of sampling of peak concentrations varied considerably ranging from immediately (12%) to 120 minutes (12%) post-infusion (median 30 minutes [40%]). The concentration-time curves resulting from three sets of mean recommendations ('peaks' drawn at: 0, 30 and 120 minutes aiming for a concentration of 35 mg/L with a trough concentration of 10 mg/L) were modelled using a two compartment Bayesian programme. The predicted true peak (maximum) concentrations ranged from 30 to 86 mg/L, despite aiming for identical target concentrations, indicating marked variation in the actual dosing practice. Conclusions: There is thus considerable variation in the practice of vancomycin therapeutic monitoring which has a major effect on dosing. The main contributing factor is the variable timing of sampling peak concentrations.