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Adjusted Body Weight Calculator

Calculate Adjusted Body Weight (AdjBW) for clinical dosing in obese patients.

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Formula

AdjBW = IBW + 0.4 * (Actual Weight - IBW)

Adjusts weight to account for the slower distribution of certain drugs in fat tissue.

Worked Example

IBW 70kg, Actual 100kg -> AdjBW 82kg.

Adjusted Body Weight (AdjBW)

Adjusted Body Weight is used to calculate drug dosages (particularly for aminoglycosides and some oncology drugs) in patients whose actual weight is significantly greater than their ideal body weight.
  • Formula: AdjBW (kg) = IBW + 0.4 × (Actual Weight - IBW)
  • It is typically used when Actual Weight is >20-30% above Ideal Body Weight
  • The 0.4 factor (40%) represents the estimated volume of distribution in adipose tissue for specific drugs
  • Ideal Body Weight (Devine) is used as the baseline for the calculation

AdjBW is a pharmacology-specific metric. Dosage adjustments should always follow established clinical guidelines for each specific medication.

You can also calculate changes using our Ideal Weight Calculator or Creatinine Clearance Calculator.

Frequently Asked Questions

When is AdjBW used?

It is used for dosing certain hydrophilic medications in obese patients to prevent toxicity that might occur if actual body weight were used.

Why the 0.4 factor?

Research suggests that for many drugs, only about 40% of excess body weight (fat tissue) contributes to the drug's volume of distribution compared to lean tissue.

Is AdjBW the same as Lean Body Mass?

No. Lean Body Mass is an estimate of total non-fat tissue, while Adjusted Body Weight is a calculated weight used specifically for pharmacokinetics.

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