The use of normalized body weight to determine antibiotic dose

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To evaluate the ability of body-weight-driven renal function assessment (RFA) formulae to predict on-target elimination rate ranges for gentamicin in patients with varying degrees of renal function” Ariano et al (2017).

Abstract:

Objectives: To evaluate the ability of body-weight-driven renal function assessment (RFA) formulae to predict on-target elimination rate ranges for gentamicin in patients with varying degrees of renal function.

Methods: A 6 year retrospective pharmacokinetic study was conducted at a university teaching hospital.

Results: A total of 85 patients met the inclusion criteria and 127 pharmacokinetic files were analysed from patients on medical-surgical wards (53%) and medical-surgical ICUs (13%) receiving intravenous gentamicin for treatment, as well as those for patients receiving it for surgical prophylaxis (34%). Each RFA formula was examined against standard dosing tables for gentamicin. A table of acceptable elimination rates was generated using a traditional peak of 8 mg/L and trough between 0.5 and 2 mg/L associated with each of the dosing interval extensions. The ability of each RFA formula to select on-target elimination rates was evaluated. The RFA formula assuming a normalized body weight of 72 kg and a modified creatinine reagent adjustment factor of 90% provided the most accurate on-target elimination rate selection. This method was superior to dosing interval selection based on the Modification in Diet Renal Disease (MDRD) formula, Sanford’s guide method, as well as the Cockcroft–Gault formulae using total body weight, ideal body weight or lean body weight (P < 0.0001).

Conclusions: Based on the use of gentamicin as a surrogate guide for renally adjusted drugs, these results support dosing interval selection based on a normalized body weight method and a formula reagent adjustment factor of 90% within the Cockcroft–Gault formula.

Reference:

Ariano, R.E., Zelenitsky, S.A., Poncsak, K.R., Davis, J.C. and Vercaigne, L.M. (2017) No role for patient body weight on renal function assessment for drug dosing. Journal of Antimicrobial Chemotherapy. 72(6), p.1802-1811.

DOI: https://doi.org/10.1093/jac/dkx036

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