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Adjusted body weight

Ideal body weight (Devine) plus 40 % of the excess weight, for overweight patients

Sources last checked: 2026-11-03

Adjusted body weight

Ideal body weight (Devine) plus 40 % of the excess weight, for overweight patients

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The 0.4 factor was derived for aminoglycoside distribution volume; other drugs use other weights or factors, and the product information or local protocol decides which weight applies. Defined for patients heavier than their ideal weight. This tool gives a weight, not a dose.

Source: Traynor AM, Nafziger AN, Bertino JS Jr. Aminoglycoside dosing weight correction factors for patients of various body sizes. Antimicrob Agents Chemother 1995;39(2):545-548 (IBW + 40 % of excess weight from prior work; 0.43 in their cohort).Open

What is the Adjusted body weight?

Adjusted body weight adds a fraction of the excess weight to the ideal body weight, on the reasoning that adipose tissue takes up some, but not all, of certain drugs. The 40 % factor comes from aminoglycoside pharmacokinetics in obese patients; Traynor and colleagues (1995) confirmed a similar factor (0.43) in 1,708 patients. Ideal body weight here is the Devine (1974) equation.

When to use it

  • When a protocol or product information specifies adjusted body weight for an obese patient
  • Aminoglycoside-type pharmacokinetic reasoning in overweight patients
  • Comparing actual, ideal, adjusted and lean weight for the same patient

When not to use it

  • Patients at or below ideal body weight — the adjustment is defined for overweight patients
  • Drugs whose labelling specifies actual or lean body weight
  • Children

How it is calculated

IBW (Devine) = 50 kg (men) or 45.5 kg (women) + 2.3 kg × (height in inches − 60) Adjusted body weight = IBW + 0.4 × (actual weight − IBW)

Clinical pearls and limitations

  • The 0.4 factor was derived for aminoglycoside distribution volume; other drugs use other weights or factors, and the product information or local protocol decides which weight applies. Defined for patients heavier than their ideal weight. This tool gives a weight, not a dose.
  • The 0.4 factor is drug-class specific; there is no universal 'obese weight'.
  • The Devine IBW equation is the same as the ARDSNet predicted body weight used for tidal volume (0.91 kg per cm ≈ 2.3 kg per inch).
  • IBW from Devine becomes implausibly low in short adults (below about 152 cm).
  • This gives a weight, not a dose — the dose depends on the drug, renal function and local protocol.

Frequently asked questions

What is the formula for adjusted body weight?

IBW + 0.4 × (actual weight − IBW), with IBW from Devine: 50 kg (men) or 45.5 kg (women) + 2.3 kg per inch above 5 feet.

When do you use adjusted body weight?

When a drug protocol specifies it for obese patients — classically aminoglycosides; many other drugs use actual or lean body weight instead.

Is ideal body weight the same as predicted body weight?

For practical purposes yes: the ARDSNet PBW equation is Devine's IBW rewritten for centimetres.

Evidence and guidelines

  1. Primary source: Traynor AM, Nafziger AN, Bertino JS Jr. Aminoglycoside dosing weight correction factors for patients of various body sizes. Antimicrob Agents Chemother 1995;39(2):545-548 (IBW + 40 % of excess weight from prior work; 0.43 in their cohort).
  2. Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm 1974;8:650-655 (ideal body weight equation).
  3. Bauer LA, Edwards WA, Dellinger EP, Simonowitz DA. Influence of weight on aminoglycoside pharmacokinetics in normal weight and morbidly obese patients. Eur J Clin Pharmacol 1983;24(5):643-647.

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For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.