Augmented Renal Clearance in Severe Infections—An Important Consideration in Vancomycin Dosing: A Narrative Review

β-Lactams are routinely used as empirical therapy in critical illness, with extended concentrations above the minimum inhibitory concentration (MIC) of the infecting organism required for effective treatment. Changes in renal function in this setting can significantly impact the probability of achieving such targets. Analysis was made of trough plasma drug concentrations obtained via therapeutic drug monitoring, compared with renal function, in critically ill patients receiving empirical β-lactam therapy. Drug concentrations were measured by means of high-performance liquid chromatography and corrected for protein binding. Therapeutic levels were defined as greater than or equal to MIC and greater than or equal to four times MIC (maximum bacterial eradication), respectively. Renal function was assessed by means of an 8-h creatinine clearance (CLCR). Fifty-two concurrent trough concentrations and CLCR measures were used in analysis. Piperacillin was the most frequent β-lactam prescribed (48%), whereas empirical cover and Staphylococcus species were the most common indications for therapy (62%). Most patients were mechanically ventilated on the day of study (85%), although only 25% were receiving vasopressors. In only 58% (n = 30) was the trough drug concentration greater than or equal to MIC, falling to 31% (n = 16) when using four times MIC as the target. CLCR values ≥ 130 mL/min/1.73 m2 were associated with trough concentrations less than MIC in 82% (P < .001) and less than four times MIC in 72% (P < .001). CLCR remained a significant predictor of subtherapeutic concentrations in multivariate analysis. Elevated CLCR appears to be an important predictor of subtherapeutic β-lactam concentrations and suggests an important role in identifying such patients in the ICU.

The current vancomycin therapeutic guidelines recommend the use of only trough concentrations to manage the dosing of adults with Staphylococcus aureus infections. Both vancomycin efficacy and toxicity are likely to be related to the area under the plasma concentration-time curve (AUC). We assembled richly sampled vancomycin pharmacokinetic data from three studies comprising 47 adults with various levels of renal function. With Pmetrics, the nonparametric population modeling package for R, we compared AUCs estimated from models derived from trough-only and peak-trough depleted versions of the full data set and characterized the relationship between the vancomycin trough concentration and AUC. The trough-only and peak-trough depleted data sets underestimated the true AUCs compared to the full model by a mean (95% confidence interval) of 23% (11 to 33%; P = 0.0001) and 14% (7 to 19%; P < 0.0001), respectively. In contrast, using the full model as a Bayesian prior with trough-only data allowed 97% (93 to 102%; P = 0.23) accurate AUC estimation. On the basis of 5,000 profiles simulated from the full model, among adults with normal renal function and a therapeutic AUC of ≥400 mg · h/liter for an organism for which the vancomycin MIC is 1 mg/liter, approximately 60% are expected to have a trough concentration below the suggested minimum target of 15 mg/liter for serious infections, which could result in needlessly increased doses and a risk of toxicity. Our data indicate that adjustment of vancomycin doses on the basis of trough concentrations without a Bayesian tool results in poor achievement of maximally safe and effective drug exposures in plasma and that many adults can have an adequate vancomycin AUC with a trough concentration of <15 mg/liter.