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General MedicineAjBW40

Adult Adjusted Body Weight Calculator (AjBW 0.4)

Calculate fixed adult AjBW40 dosing-weight arithmetic from total body weight and either an existing or optional Devine ideal body weight, with drug- and protocol-specific limitations.

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Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.

The default path keeps the current external-IBW workflow. Choose the Devine path only when that historical reference-weight method is the one required by the applicable protocol.

Adjusted body weight — fixed 0.4 model (AjBW40)

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Fixed AjBW40 arithmetic; not a dose or applicability decision.

About

AjBW40 is fixed adult dosing-weight arithmetic that adds 40% of the difference between total body weight (TBW) and ideal body weight (IBW) to the entered IBW. It is not a direct body-composition measurement and does not choose a medicine, establish that adjusted body weight applies, or calculate a dose. You may enter an IBW from an external protocol or calculate the historical Devine reference-weight IBW here before applying the fixed AjBW40 arithmetic. [1, 2, 3, 6]

Formula

AjBW40 = IBW + 0.4 × (TBW − IBW) [1, 3]
This page fixes C at 0.4 and does not select a drug, protocol, IBW method, eligibility threshold, or dose. [2, 3]
Optional local IBW path: Devine's adult height-and-sex reference formula supplies the IBW, which is then passed to the same AjBW40 calculation. The page does not infer the coefficient or claim that Devine is required by every protocol. [6]

Interpretation

Fixed 0.4 arithmetic

Traynor and colleagues estimated an aminoglycoside correction factor near 0.43. Using 0.4 is a common simplification, not a universally exact constant. [1, 3]

Drug-specific weight descriptor

Depending on the medicine and applicable source, dosing may use TBW, IBW, AjBW, lean body weight, fixed dosing, or another method. [2, 3]

No universal 120% threshold

TBW as a percentage of IBW is displayed only to audit the entered values. It does not automatically determine whether AjBW applies; a 120% rule can be institution-, medicine-, and process-specific. [5]

IBW source is explicit

The default path accepts an externally determined IBW. An optional local path calculates historical Devine IBW from height and the explicitly selected published coefficient before sending it to AjBW40; another protocol may require another method. [2, 6]

Not a medication dose

The output does not calculate mg/kg, a total dose, a dose cap, renal adjustment, dosing interval, or monitoring plan. [2, 3, 4]

Drug-specific examples — not calculated

Aminoglycosides are a typical context in which a specific adult protocol may use AjBW40. An initial weight scalar does not replace renal-function assessment, and later dosing may require therapeutic drug monitoring; this page does not calculate a dose. [1, 3]

As a contrast, the 2020 consensus guidance for serious MRSA infections uses AUC-guided vancomycin monitoring and recommends actual-body-weight loading in specified settings. Fixed AjBW40 cannot replace that guidance. [4]

UCSF's 120%-of-IBW example is an institution-, medicine-, and process-specific rule. This calculator does not convert it into a universal eligibility threshold. [5]

References

  1. Traynor AM, Nafziger AN, Bertino JS Jr. Aminoglycoside dosing weight correction factors for patients of various body sizes. Antimicrobial Agents and Chemotherapy. 1995;39(2):545–548. PMID 7726530. PMCID PMC162577. doi:10.1128/AAC.39.2.545.
  2. Pai MP. Drug dosing based on weight and body surface area: mathematical assumptions and limitations in obese adults. Pharmacotherapy. 2012;32(9):856–868. PMID 22711238. doi:10.1002/j.1875-9114.2012.01108.x.
  3. Castro-Balado A, et al. Updated antimicrobial dosing recommendations for obese patients. Antimicrobial Agents and Chemotherapy. 2024;68(5):e01719-23. PMID 38526051. PMCID PMC11064535. doi:10.1128/aac.01719-23.
  4. Rybak MJ, et al. Therapeutic monitoring of vancomycin for serious MRSA infections: revised consensus guideline and review. American Journal of Health-System Pharmacy. 2020;77(11):835–864. PMID 32191793. doi:10.1093/ajhp/zxaa036.
  5. UCSF Infectious Diseases Management Program. Dosing Weights. Current institution- and drug-specific resource. Accessed August 15, 2026.
  6. Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. Annals of Pharmacotherapy. 2000;34(9):1066–1069. PMID 10981254. doi:10.1345/aph.19381.

FAQ

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Disclaimer

Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.