Background Pharmacokinetic studies have suggested that total body weight (TBW) could be the optimal approach to calculate the dose of intravenous vancomycin (15–20 mg/kg TBW every 8–12 h) for target achievement (Css > 15 mg/L).1 However, recent data concluded that the use of adjusted body weight (ABW) might be a better approach in obese patients.2
Purpose To determine which is the preferred method (TBW, ideal body weight (IBW) or ABW) to optimise vancomycin treatment in obese patients.
Material and methods Retrospective, non-interventional, observational study. Inclusion criteria: >18 years-old, body-mass-index (BMI) ≥30 kg/m2, creatinine clearance ≥60 mL/min, and vancomycin TDM at steady-state. Non-obese patients were included as a control group. Patients were identified by reviewing TDM reports.
Vancomycin theoretical total daily doses (15–20 mg/kg) were calculated using TBW, IBW and ABW for each patient. They were compared with the dose used in our patients after TDM (Bayesian forecasting; PKSAbbot Software; target: Css > 15 mg/L) (TDM dose).
Dose differences greater than 10–12.5% of the TDM dose were considered unsuitable, since they could be related to clinical failure. Wilcoxon’s test analysis was performed using SPSS; (p < 0.05).
Results Forty obese patients: 35% men; 60.4 ± 12.6 years-old; BMI: 33.3 ± 2.7 kg/m2.
Compared to the TDM dose and considering 15–20 mg/kg:
(i) Overdosage was observed in 72.5 (95%), 25 (47.5%) and 32.5 (72.5%) patients for TBW, IBW and ABW, respectively. Statistically significant differences were seen, with mean dose differences higher than 500 mg in the 20 mg/kg group.
(ii) Underdosage was seen in: 22.5 (5.0%), 75 (45%) and 67.5 (27.5%) respectively.
Statistically significant differences were seen with mean dose differences lower than 400 mg in the 15 mg/kg group.
No relevant differences were observed in the control group.
Conclusion Compared to the TDM dose, a high incidence of overdosage would be observed by using TBW. In our obese patient cohort, ABW might be the best approach to set the dose of intravenous vancomycin (15–20 mg/kg), as already seen in previous literature.2
Rybak M, Lomaestro B, Rotschafer JC, et al. Therapeutic monitoring of vancomycin in adult patients: a consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Am J Health Syst Pharm 2009;66:82–98
Leong JV, Boro MS, Winter M, et al. Determining vancomycin clearance in an overweight and obese population. Am J Health Syst Pharm 2011;68:599–603
ReferencesNo conflict of interest.
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