Vancomycin Dosing Considerations in a Real-World Cohort of Obese and Extremely Obese Patients.

STUDY OBJECTIVE: To compare the effects of empiric vancomycin dosing regimens on attainment of optimal target trough concentrations in obese (body mass index [BMI] 30-40 kg/m(2) ) and extremely obese (BMI ≥ 40 kg/m(2) ) patients.

DESIGN: Retrospective cohort study.

DATA SOURCE: National Veterans Affairs standardized databases.

PATIENTS: A total of 263 obese and 71 extremely obese (actual body weight range 72-244 kg in both groups) inpatients from all Veterans Affairs facilities nationally who had suspected methicillin-resistant Staphylococcus aureus pneumonia and were treated with vancomycin between 2002 and 2012.

MEASUREMENTS AND MAIN RESULTS: Patients with steady-state trough concentrations (measured ≤ 2 hours before the next vancomycin dose) and no evidence of acute kidney injury before vancomycin initiation were included. Logistic regression models were used to measure the effect of various vancomycin dosing regimens on attainment of optimal target trough concentrations (15-20 mg/L). The mean total daily vancomycin dose was lower in obese versus extremely obese patients (2005 ± 736 vs 2306 ± 934 mg, p<0.05). The mean weight-based daily dose was higher in obese patients (20 ± 7 vs 17 ± 7 mg/kg/day, p<0.05). In each group, ~ 20% of patients achieved optimal target trough concentrations. In obese patients, the standard dose of ~ 30 mg/kg/day was appropriate for target trough concentration attainment (odds ratio 5.15, 95% confidence interval 1.69-15.64). In extremely obese patients, a lower dosage of 20 to 25 mg/kg/day was appropriate for target trough concentration attainment (odds ratio 6.07, 95% confidence interval 1.01-36.51).

CONCLUSION: In this real-world study, we offer additional consideration of vancomycin dosing in obese and extremely obese patients. Extremely obese patients may require a lower weight-based daily dose than obese patients to reach target vancomycin trough concentrations.