Adjusted Body Weight (AdjBW) is used for drug dosing in obese patients (typically when actual body weight exceeds 120% of ideal body weight). It accounts for the fact that adipose tissue contributes to drug distribution but not as much as lean tissue.
Formula
AdjBW = IBW + 0.4 × (Actual Weight − IBW)
When to Use AdjBW
- Aminoglycoside dosing (gentamicin, tobramycin, amikacin)
- Vancomycin dosing in patients >120% IBW
- Some chemotherapy protocols
- Drug dose calculations involving body water distribution
Why 0.4?
The 0.4 correction factor reflects that adipose tissue contributes approximately 40% to the drug's volume of distribution for water-soluble medications. This correction prevents both underdosing (using IBW) and overdosing (using actual weight) in obese patients.