Question 1

What is the Devine formula for ideal body weight?

Accepted Answer

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.

Question 2

When should I use adjusted body weight instead of actual or ideal?

Accepted Answer

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.

Question 3

What weight do I use for tidal volume in ARDS?

Accepted Answer

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.

Question 4

Why use lean body weight for propofol?

Accepted Answer

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.

Weight	kg
Actual	90.0
Ideal (Devine)	70.5
AdjustedIBW + 0.4 × (Actual − IBW)	78.3
Lean (Janmahasatian)	64.0

IBW / Adjusted / Lean Body Weight

References

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