Aminoglycoside dosing and kidney function: which equation to use?

Letter

Thank you for your insightful article on aminoglycosides.¹ I noted with interest the recommendation to use the Cockcroft–Gault equation, with different weight descriptors depending on body mass index, for calculating aminoglycoside doses in relation to kidney function, citing a paper by Winter et al.² However, another paper cited in the article (Pai et al.)³ suggests improved prediction of aminoglycoside clearance using estimated glomerular filtration rate (eGFR) rather than estimated creatinine clearance. Similarly, Lim et al.⁴ found that the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation adjusted for body surface area best predicts aminoglycoside clearance.

I would be interested in your thoughts on reconciling these differing approaches.

Janice Chiang
Antimicrobial Stewardship Pharmacist, Barwon Health, Geelong

Conflicts of interest: none declared

 

References

1. Moore H, Yeoh D, Hughes C, Raby E, Sandaradura I. Aminoglycosides: an update on indications, dosing and monitoring. Australian Prescriber 2025;48:133-8.
2. Winter MA, Guhr KN, Berg GM. Impact of various body weights and serum creatinine concentrations on the bias and accuracy of the Cockcroft-Gault equation. Pharmacotherapy 2012;32:604-12.
3. Pai MP, Nafziger AN, Bertino JS, Jr. Simplified estimation of aminoglycoside pharmacokinetics in underweight and obese adult patients. Antimicrob Agents Chemother 2011;55:4006-11.
4. Lim AK, Mathanasenarajah G, Larmour I. Assessment of aminoglycoside dosing and estimated glomerular filtration rate in determining gentamicin and tobramycin area under the curve and clearance. Intern Med J 2015;45:319-29.

 

Author's response

Indy Sandaradura, one of the authors of the article, comments:

Thank you for your letter. We acknowledge the uncertainty in determining the optimal approach for aminoglycoside dosing. As you rightly pointed out, different equations such as the Cockcroft–Gault equation, eGFR and CKD-EPI have been recommended in various studies, each with its own merits and limitations. This variability underscores the need for a consistent approach to dosing that considers kidney function.

The recommendation to use Cockcroft–Gault in Therapeutic Guidelines: Antibiotic was primarily to ensure consistency across the guideline and with other external guidelines. Additionally, using Cockcroft–Gault to estimate creatinine clearance requires adjustment for body size, which is often forgotten when using eGFR, which is indexed to a body surface area of 1.73 m².

In practice, we emphasise the importance of early consultation and therapeutic drug monitoring for patients with challenging clinical scenarios. This approach helps to tailor the dosage regimen to the individual patient's needs, ensuring both efficacy and safety. We believe that maintaining a consistent methodology for dosing, while being open to adjustments based on therapeutic drug monitoring and clinical judgement, is crucial for optimal patient outcomes.

 

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