What is Adjusted Body Weight?
**Adjusted Body Weight (AjBW)** corrects for the fact that *adipose tissue* (fat) is less metabolically active and holds less water than lean tissue.
The Clinical Risk:
Using Actual Weight for obese patients risks toxicity (Overdosing), while using Ideal Weight risks treatment failure (Underdosing). AjBW provides the safe middle ground.
The Formula (The 0.4 Standard)
AjBW = IBW + 0.4 × (Actual - IBW)
The **0.4 correction factor** estimates that approximately **40% of excess body weight** contributes to drug clearance and distribution volume. This is the global standard for pharmacokinetics.
When to Use It (2025 Guidelines)
Antibiotics Dosing
Standard for Aminoglycosides (Gentamicin, Tobramycin) in obese patients, as per Stanford 2025 protocols. It ensures therapeutic levels without renal toxicity.
Nutrition (ESPEN)
ESPEN Guidelines often recommend Adjusted Weight for energy calculations in metabolic obesity. Note that ASPEN guidelines may differ (often using 65-70% of estimated needs).
Frequently Asked Questions
When is a patient considered obese for dosing?
Why do we use the 0.4 correction factor?
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: December 2025.