Individualized vancomycin dosing in obese patients: a two-sample measurement approach improves target attainment

Study objective: To compare the likelihood of vancomycin target trough concentration attainment based on infectious diagnosis and/or minimum inhibitory concentration for the organism by using a two-sample approach versus the prior institutional standard of a trough-only approach in obese patients receiving vancomycin.

Design: Preintervention and postintervention study.

Setting: Community acute care hospital.

Patients: One hundred fifty hospitalized adults with a body mass index (BMI) of 30 kg/m(2) or greater and treated with vancomycin for at least 48 hours between July 2013 and March 2014 were evaluated to compare the frequency of steady-state therapeutic trough concentration attainment between two approaches: a trough-only dosing method (preintervention group [75 patients]) and a dosing strategy measuring two vancomycin serum concentrations during the elimination phase (peak and trough) to calculate pharmacokinetic parameters and individualize the maintenance regimen (postintervention group [75 patients]). Data for the preintervention group were retrospectively retrieved from a 4-month period for patients admitted between July and October 2013, prior to implementation of the two-point vancomycin dosing protocol. Initial vancomycin empiric dose selection for both groups utilized the same population-based pharmacokinetic equations.

Measurements and main results: Median (5th-95th percentile) age, weight, and BMI were 59 (34-80) years, 105 (79.8-164) kg, and 34.5 (30.0-55.1) kg/m(2) , respectively, for all patients. The percentages of initial therapeutic trough concentrations achieved in the preintervention and postintervention groups were 32.0% and 42.7%, respectively (p=0.117). For patients with a second trough measurement, 31.0% in the preintervention group and 65.2% in the postintervention group were within the therapeutic range (p=0.024).

Conclusion: Measurement of two serum vancomycin concentrations significantly improves subsequent target trough concentration attainment in the obese population.