Optimizing the dosing of vancomycin in patients receiving intermittent haemodialysis with low-flux filters, and the potential impact of dosing software.

AIM: Iterative approaches to vancomycin dosing (e.g., dosing when trough concentrations <15-20 mg/L) can be inadequate. Computer-guided dosing may be superior but has not been evaluated in patients with kidney failure receiving replacement therapy. We evaluated vancomycin concentrations using a hospital protocol and a pharmacokinetic software. We measured vancomycin clearance by the FX8 low-flux filter because data are absent.

METHODS: We retrospectively reviewed records of adults with kidney failure requiring replacement therapy receiving vancomycin and dialysed with the FX8 low-flux filter, and calculated the proportion of pre-dialysis concentrations that were within, above or below a specified range. One and two-compartment models in the pharmacokinetic software were assessed by computing mean prediction error (MPE) and root mean square error (RMSE) of observed versus predicted concentrations. Vancomycin extracorporeal clearance was prospectively determined using the extraction method.

RESULTS: In 24 patients (34 courses; 139 paired observed and predicted concentrations), 62/139 (45%) pre-dialysis concentrations were 15-25 mg/L, 29/139 (21%) were above, and 48/139 (35%) were below. MPE for the one-compartment model was -0.2 mg/L, RMSE 5.3 mg/L. MPE for the two-compartment model was 2.0 mg/L, RMSE 5.6 mg/L. Excluding the first paired concentrations, the subsequent MPE (n = 105) using one-compartment model was -0.5 mg/L, RMSE 5.6 mg/L. The MPE for the two-compartment model was 2.1 mg/L, RMSE 5.8 mg/L. The median extracorporeal clearance was 70.7 mL/min (range: 10.3-130.3; n = 22).

CONCLUSIONS: Vancomycin dosing was suboptimal and the pharmacokinetic software was not sufficiently predictive. These may improve with a loading dose. The substantial removal of vancomycin by low-flux filters is not accounted for by the models tested.