VANCOMYCIN SERUM CONCENTRATION MONITORING - THE MIDDLE GROUND IS BEST

The recent increase in the use of vancomycin has led to renewed intere st in its pharmacokinetics, and, in particular, the importance of moni toring serum drug concentrations. A review of the literature and evalu ation of pharmacokinetic data from Vancouver Hospital and Health Scien ces Centre demonstrated that vancomycin meets the criteria necessary f or serum drug concentration monitoring. These include the availability of a sensitive and specific assay, substantial interpatient and intra patient variability in drug disposition, and evidence suggesting a cor relation between vancomycin serum concentration and both efficacy and toxicity. A review of vancomycin disposition data for 371 consecutive treatment courses at this hospital revealed significant interpatient v ariability in drug clearance and volume of distribution. Accordingly, it would be difficult to accurately predict the change in serum concen tration resulting from a given vancomycin dose. There appears to be le ss intrapatient variability in volume of distribution; however, serum elimination half-life tends to increase during treatment, necessitatin g an alteration in dose interval. Although convenient, physiological p arameters to monitor serum creatinine concentration and bodyweight are not accurate predictors of drug clearance and volume of distribution. Serum concentration monitoring is also necessary to ensure that vanco mycin concentrations are in excess of the minimum inhibitory concentra tion of the organism at all times during treatment. Although a causal relationship between vancomycin and toxicity has been difficult to pro ve, there is some evidence in the literature to support a relationship between high troughs and nephrotoxicity. In view of the available evi dence, we do not believe that serum concentration monitoring should be totally abandoned. We have created empiric dosage guidelines and a de cision-making algorithm for serum drug concentration monitoring that h ave streamlined the process of drug prescribing and monitoring at this institution.