IBW / Adjusted / Lean Body Weight
Devine ideal body weight, adjusted body weight, and Janmahasatian lean body weight with dosing-weight guidance.
- Dosing aminoglycosides, vancomycin, enoxaparin, or any drug with a weight-based prescribing convention
- Setting tidal volume targets in mechanical ventilation (6 mL/kg IBW for ARDS)
- Anesthesia induction in obesity (propofol, neuromuscular blockers)
- Quick gut-check that the home weight on a chart isn't being misapplied
- The Devine formula for IBW is the convention even though its origins are pharmacy mythology rather than rigorous derivation. It works reasonably well in adults of typical height.
- Adjusted body weight with a 0.4 correction is the most common factor for hydrophilic drugs in obesity, but specific protocols use 0.3 or 0.5 — verify the agent in question.
- Lean body weight is what you want for lipophobic anesthetic dosing. Older Hume / James equations are still widely cited but break at high BMI; Janmahasatian's is preferred.
- Tidal volume in ARDS uses predicted (≈ ideal) body weight, not actual — this is one of the easiest dosing errors to make on rounds.
Drug dosing in obesity is one of the most consistently miscalculated things on the wards. Showing all four weights side by side — with a heuristic suggestion based on % over IBW — makes the "which weight do I use?" question concrete instead of abstract.
| Weight | kg |
|---|---|
| Actual | 90.0 |
| Ideal (Devine) | 70.5 |
| AdjustedIBW + 0.4 × (Actual − IBW) | 78.3 |
| Lean (Janmahasatian) | 64.0 |
BMI
29.4kg/m²
% over IBW
28%
Suggested dosing weight: 70.5 kg (ideal body weight)
Modest overweight. Many lipophobic / hydrophilic drugs (aminoglycosides, vancomycin LD) traditionally use IBW.
Drug-specific: aminoglycosides, vancomycin, enoxaparin, propofol, sugammadex, neuromuscular blockers all have different conventions. Verify against institutional protocol.
Frequently asked
What is the Devine formula for ideal body weight?
For men: IBW (kg) = 50 + 2.3 × (height in inches − 60). For women: IBW (kg) = 45.5 + 2.3 × (height in inches − 60). Originally published by Devine in 1974 as a pharmacy reference, this formula has become the de facto standard for weight-based drug dosing despite limited prospective validation.
When should I use adjusted body weight instead of actual or ideal?
Adjusted body weight (ABW = IBW + 0.4 × (Actual − IBW)) is most commonly used when a patient is more than ~20–30% over their IBW and the drug is hydrophilic — aminoglycosides and unfractionated heparin in obesity are classic examples. The 0.4 factor accounts for the partial contribution of adipose tissue to drug distribution.
What weight do I use for tidal volume in ARDS?
Use predicted (ideal) body weight, not actual. The ARDSNet protocol targets 6 mL/kg of predicted body weight. Using actual body weight in obesity systematically overinflates the lungs and undermines the lung-protective strategy.
Why use lean body weight for propofol?
Propofol is highly lipophilic but its induction dose correlates with lean mass, not fat mass. Dosing on actual body weight in obesity leads to overdosing and prolonged emergence; dosing on IBW underdoses. Janmahasatian lean body weight tracks pharmacokinetic exposure more accurately at high BMI.