Daily vancomycin dose requirements as a continuous infusion in obese versus non-obese SICU patients

BACKGROUND: Limited data are available assessing vancomycin concentrations in obese critically ill patients. Currently, there are no studies evaluating dosing requirements in this population who receive vancomycin administered as a continuous infusion (CI). The aim of this study was to assess whether there was a difference in the weight-based maintenance dose required to reach a therapeutic vancomycin concentration at 24 hours when given as a CI in obese versus non-obese critically ill patients. METHODS: A retrospective cohort study of adult obese patients admitted to the SICU between 2013 and 2015 receiving a vancomycin CI (CIV), and with 24-hour serum measurements were included. Obese patients (body mass index (BMI) ≥35 kg/m(2)) were matched with non-obese patients (BMI <30 kg/m(2)) based on renal function, age and acute physiology and chronic health evaluation (APACHE)-II score at admission. All patients in this study received a loading dose of 25 mg/kg then a maintenance dose based on renal function according to the protocol. The study was approved by the Institutional Review Board. The primary outcome was the weight-based total daily maintenance dose required to achieve a vancomycin level of 20 mg/L. The secondary endpoints included the achievement of a therapeutic level at 24 hours. RESULTS: Twenty-six matched pairs of patients met the inclusion criteria. Of these, 17 pairs had preserved renal function and 9 pairs required continuous venovenous hemofiltration. Mean BMI was 40.9 kg/m(2) in obese and 24.8 kg/m(2) in non-obese patients. To achieve a vancomycin concentration of 20 mg/L, the weight-based daily maintenance dose in obese patients was 25.6 mg/kg versus 43.8 mg/kg in non-obese patients (p <0.01). Therapeutic 24-hour levels were achieved in 24/26 obese versus 23/26 no-obese patients (p = 0.63). Mean 24-hour vancomycin level was 20.3 ± 3.81 mcg/ml in obese compared to 20.03 ± 3.79 mcg/ml in non-obese patients (p = 0.77). Mean daily maintenance doses required to achieve a level of 20 mcg/ml were 2961 ± 1670 mg in obese compared to 3189 ± 1600.69 mg in non-obese (p = 0.61). CONCLUSIONS: The results of our study suggest that critically ill obese patients treated with CIV required a significantly lower maintenance dose per unit of body weight than non-obese patients to achieve the same target level.