Background: A revised consensus guideline on therapeutic drug monitoring (TDM) of vancomycin for serious methicillin-resistant Staphylococcus aureus (MRSA) infections was recently published with endorsement of numerous American pharmacy and medical societies. Changing practice from trough TDM to area-under-the-curve-(AUC)-guided dosing was suggested. Methods: Recent literature was critically appraised to determine whether AUC TDM is appropriate for Canadian hospital practice. Results: Previous 2009 vancomycin consensus guidelines recommended trough levels of 15–20 mg/L for serious MRSA infections, based on relatively poor evidence for efficacy or safety. In the past decade, aggressive trough targets have led to unnecessary toxicity. Adoption of a TDM strategy using an alternative parameter (AUC) has been suggested, although the evidence for any outcome benefits is low quality. In addition, implementation would require greater resources at health care institutions in the forms of more frequent serum levels or acquisition of costly Bayesian software programs. Most studies on this subject have been observational and retrospective; therefore, relationships between TDM parameters and outcomes have not been convincingly and consistently demonstrated to be causal in nature. Despite claims to the contrary, based on few in silico experiments, available clinical data suggest correlation of trough levels and AUC is high. TDM with lower target trough levels is a simpler solution to reduce risk of toxicity. Conclusions: There are serious concerns with adoption of AUC TDM of vancomycin into routine practice in Canada. Trough-based monitoring with modest reduction in target levels remains the most evidence-informed practice at this time.
The revised vancomycin guidelines recommend implementing AUC24-based therapeutic drug monitoring (TDM) using Bayesian methods in both adults and paediatrics. The motivation for this change was accumulating evidence showing aggressive dosing to achieve high troughs, as recommended in the first guidelines for adults and extrapolated to paediatrics, is associated with increased nephrotoxicity without improving clinical outcomes. AUC24-based TDM requires substantial resources that may need to be diverted from other valuable interventions. It can therefore be justified only after certain assumptions are shown to be true: (i) there is a clear relationship between vancomycin efficacy and/or toxicity and the proposed therapeutic range; and (ii) maintaining exposure within the target range with AUC24-based TDM improves clinical outcomes and/or decreases toxicity. In this review, we critically appraise the scientific basis for these assumptions. We find studies evaluating the relationship between vancomycin AUC24/MIC and efficacy in adults and children do not offer strong support for the recommended lower limit of the proposed therapeutic range (i.e. AUC24/MIC ≥400). Nephrotoxicity in children increases in a stepwise manner along the vancomycin exposure continuum but it is unclear if one parameter (AUC24 versus trough) is a superior predictor. Overall, evidence in children suggests good-to-excellent correlation between AUC24 and trough. Most importantly, there is no convincing evidence that the method of vancomycin TDM has a causal role in improving efficacy or reducing toxicity. These findings question the need to transition to resource-intensive AUC24-based TDM over retaining trough-based TDM with lower targets to minimize nephrotoxicity in paediatrics.
In the modern era of rapid advances in the field of antimicrobial ‘precision dosing’ through therapeutic drug monitoring (TDM), there is growing pressure to adopt new technologies and expand the number of antimicrobials managed with TDM and/or the complexity of TDM methods. For many clinicians, it may seem inevitable that TDM must improve patient outcomes. However, based on the evidence to date, this concept remains largely a hypothesis. Conversely, it is plausible that focusing on TDM may distract from careful clinical monitoring of the patient for efficacy and drug-related toxicities and shift finite resources from other valuable interventions. In this article we make the case for embracing critical appraisal of precision dosing, remaining skeptical until persuaded by compelling evidence, and adopting new technologies only when they have proven their value over competing priorities; that is, we make the case for using ‘conservative pharmacotherapy’.
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