Implementation of a protocol for administration of vancomycin by continuous infusion: pharmacokinetic, pharmacodynamic and toxicological aspects.

Optimising antibiotic administration is critical when dealing with pathogens with reduced susceptibility. Vancomycin activity is dependent on the area under the concentration-time curve over 24 h at steady-state divided by the minimum inhibitory concentration (AUC/MIC), making continuous infusion (CI) or conventional twice daily administration pharmacodynamically equipotent. Because CI facilitates drug administration and serum level monitoring, we have implemented a protocol for CI of vancomycin by: (i) examining whether maintaining stable serum concentrations (set at 25-30 mg/L based on local susceptibility data of Gram-positive target organisms) can be achieved in patients suffering from difficult-to-treat infections; (ii) assessing toxicity (n = 94) and overall efficacy (n = 59); and (iii) examining the correlation between AUC/MIC and the clinical outcome in patients for whom vancomycin was the only active agent against a single causative pathogen (n = 20). Stable serum levels at the expected target were obtained at the population level (loading dose 20mg/kg; infusion of 2.57 g/24 h adjusted for creatinine clearance) for up to 44 days, but large intrapatient variations required frequent dose re-adjustments (increase in 57% and decrease in 16% of the total population). Recursive partitioning analysis of AUC/MIC ratios versus success or failure suggested threshold values of 667 (total serum level) and 451 (free serum level), corresponding to organisms with a MIC>1 mg/L. Nephrotoxicity potentially related to vancomycin was observed in 10% of patients, but treatment had to be discontinued in only two of them.