Evaluation of a modified vancomycin nomogram for obese adults.

PURPOSE

The purpose of this study was to compare therapeutic vancomycin trough levels in obese adults when using an original nomogram (phase I) versus a modified nomogram (phase II).

METHODS

This study compared a vancomycin nomogram with a modified vancomycin nomogram for obese adults over 100 kg. The primary endpoint compared the percentage of sub-therapeutic, therapeutic, and supra-therapeutic vancomycin trough concentrations between the nomograms. Patients were included if they were at least 18 years of age, had a total body weight of 100-299 kg, and had an initial vancomycin trough level collected. Patients were excluded if they had end-stage renal disease or were on continuous renal replacement therapy.

RESULTS

Therapeutic trough levels occurred in 85 out of 171 patients (50%) in phase I and 98 out of 149 patients (66%) in phase II. The incidence of both sub-therapeutic and supra-therapeutic troughs was less in phase II (p = 0.013). In the subgroup of adults aged 18 to 49 with a normalized creatinine clearance of greater than 90 mL/min, there was a trend in more therapeutic levels with the modified nomogram and less chance of sub-therapeutic levels (p = 0.088). In the subgroup of adults with a normalized creatinine clearance of 60-90 mL/min, there was significant improvement in therapeutic levels and a decrease in supra-therapeutic levels without increasing the percent of sub-therapeutic levels (p = 0.001).

CONCLUSION

The modified vancomycin nomogram at Cone Health showed significant improvement in therapeutic trough concentrations while reducing the rates of under and over dosing obese adults. The Cone Health-modified vancomycin nomogram could be a useful tool for initial dosing of vancomycin in the obese population.