Adjusted Body Weight Calculator
Calculate adjusted body weight for obese patients
Adjusted Body Weight (ABW) is an estimate of weight used for medication dosing in obese patients. It is calculated using:
- Actual Weight
- Ideal Weight
- Obesity Class (based on BMI)
ABW aims to improve dosing accuracy by accounting for altered pharmacokinetics in obesity.
The formula for ABW is:
ABW = Ideal Weight + Factor × (Actual Weight - Ideal Weight)
Where the factor depends on obesity class:
- Class 1 (BMI 30-34.9): Factor = 0.25
- Class 2 (BMI 35-39.9): Factor = 0.375
- Class 3 (BMI ≥ 40): Factor = 0.5
ABW is used because:
- Total body weight may overestimate lean body mass, leading to overdosing
- Ideal body weight may underestimate fat mass, leading to underdosing
- ABW provides a more accurate estimate for drugs distributed in lean tissue
What is the difference between ABW and Ideal Body Weight (IBW)?
IBW is an estimate of healthy weight based on height, while ABW adjusts actual weight towards IBW based on obesity class. ABW is more appropriate for dosing in obese individuals.
Is ABW always necessary for obese patients?
Not all medications require ABW. It is most relevant for drugs with narrow therapeutic windows or those primarily distributed in lean tissue. Consult prescribing guidelines.