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IBW-based vancomycin dosing predicts trough concentrations in severely obese patients
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Dosing vancomycin to patients with severe obesity based on ideal body weight was more accurate compared with dosing patients based on currently recommended actual body weight, according to recent findings.
“Current guidelines for systemic vancomycin dosing and monitoring recommend calculating initial doses (15-20 mg/kg every 8-12 hours) using actual body weight (ABW), regardless of BMI, followed by therapeutic drug monitoring for dose adjustments,” Michael S. Calderwood, MD, MPH, assistant professor at Brigham and Women’s Hospital and Harvard Medical School, and colleagues wrote. “In our institution, we have observed variability in the achievement of initial vancomycin serum trough concentrations between [15 mg/L and 20 mg/L] in obese patients dosed using ABW.”
Michael S. Calderwood
Calderwood and colleagues evaluated data on 67 adult patients hospitalized from January 2011 to December 2013 to determine whether the initial trough concentration is better estimated by dosing based on ABW, ideal body weight (IBW) or dosing body weight (DBW). Patients were severely obese (BMI ≥ 35 kg/m²) and treated with at least 3 consecutive doses of systemic vancomycin.
Initial vancomycin dosing based on IBW (P = .001) and DBW (P = .012) better predicted stable vancomycin trough concentrations of 15 mg/L to 20 mg/L compared with ABW, according to the researchers. When using ABW, 93% of patients (n = 62) received doses below the minimum recommendation of 30 mg/kg daily (mean of 21.2 mg/kg daily).
Further analysis adjusted for age, gender and serum creatinine showed IBW was the best predictor of initial vancomycin steady-state trough concentration.
The researchers suggested dosing vancomycin between 45 mg/kg daily and 65 mg/kg daily when using IBW as opposed to 30 mg/kg daily when using ABW. Seventy-three percent of patients who received less than 45 mg/kg daily did not reach vancomycin serum trough concentrations of at least 15 mg/L vs. only 37% of patients who received more than 45 mg/kg daily. However, 67% of patients who received more than 65 mg/kg attained elevated levels of serum trough concentrations above 20 mg/L.
“In addition, it may be preferred to select a dosing interval of 8 hours rather than 12 hours, based on prior published literature,” Calderwood and colleagues wrote. “Further well-designed pharmacokinetic studies in obese patients are desirable.” – by Jen Byrne
Disclosure: The researchers report no relevant disclosures.
Editor's Note: On Dec. 31, we updated the headline to clarify that dosing vancomycin based on IBW predicts trough concentrations in severely obese patients. The editors regret the error.
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