Validation of the Effectiveness of a Vancomycin Nomogram in Achieving Target Trough Concentrations of 15-20 mg/L Suggested by the Vancomycin Consensus Guidelines

Study Objective. To assess and validate the effectiveness of a newly constructed vancomycin dosing nomogram in achieving target trough serum concentrations of 15-20 mg/L. Design. Prospective multicenter study. Setting. Five tertiary care teaching hospitals. Patients. A total of 200 adults who required vancomycin dosages targeted to attain recommended trough vancomycin serum concentrations of 15-20 mg/L. Intervention. The new nomogram, which based dosing on weight and renal function, was used to calculate patients' initial vancomycin dosages. Serum trough concentrations were measured before the fourth or fifth dose, and dosages were adjusted as needed. Measurements and Main Results. Median patient age was 56 years (interquartile range [IQR] 49-65 yrs), median weight was 71.2 kg (IQR 63-85 kg), and median creatinine clearance was 66.5 ml/minute (IQR 52-82 ml/min). The median initial vancomycin trough concentration achieved was 17.5 mg/L (IQR 15.0-20.0 mg/L), with 116 patients (58%) achieving the initial target trough of 15-20 mg/L. The median percent error was 13.6%, and the mean +/- SD error for predicted versus actual serum trough concentrations was -0.50 +/- 0.021 mg/L. One hundred fifty-four patients (77%) eventually achieved the trough target concentration within a median of 2 days. One hundred forty patients (70%) achieved initial troughs of 14-21 mg/L and 160 (80%) achieved troughs of 13-22 mg/L. Nine patients (4.5%) experienced nephrotoxicity while receiving vancomycin, which occurred after a median of 8 days of therapy. The median initial vancomycin trough concentration for these patients was 18.5 mg/L (IQR 15.3-19.3 mg/L), with eight of the nine patients having trough concentrations of 15 mg/L or greater. Conclusion. Fifty-eight percent of patients achieved the target trough of 15-20 mg/L (median 17.5 mg/L). The performance of the nomogram improved to 80% when the trough range was adjusted to 13-22 mg/L. Caution should be applied when using this nomogram. The nomogram should not replace clinical judgment, and dosage adjustments should be based on pharmacokinetic-pharmacodynamic targets and clinical response.