Ideal Body Weight and Adjusted Body Weight

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Ideal Body Weight and Adjusted Body Weight

Estimates weight for safe drug dosing and clinical decision-making in both normal and obese patients

All tools /

Ideal Body Weight and Adjusted Body Weight

Estimates weight for safe drug dosing and clinical decision-making in both normal and obese patients

Ideal Body Weight and Adjusted Body Weight

Calculates ideal body weight (Devine formula) and adjusted body weight.

Sex

MaleFemale

Height

Actual weight

Ideal Body Weight: —

—

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Instructions

Use this tool to estimate a patient’s weight for drug dosing, fluid management, or nutritional planning. IBW is applied in normal or slightly overweight individuals, while AdjBW is considered in obesity when actual body weight greatly exceeds IBW. Choose the appropriate calculation based on the patient’s clinical context, ensuring correct medication dosing and avoiding toxicity.

Overview

When to use

Why use

Evidences

Interpretation

· IBW (men): 50 + (2.3 × [height in inches – 60])

· IBW (women): 45.5 + (2.3 × [height in inches – 60])

· AdjBW: IBW + 0.4 × (Actual Body Weight – IBW)

Scenario	Weight Metric Used
Normal weight or slight overweight	IBW
Obese patients (BMI > 30)	AdjBW
Ventilator settings	IBW
Nutrition/fluids	IBW or AdjBW (context-dependent)

Ideal Body Weight (IBW) and Adjusted Body Weight (AdjBW) are anthropometric constructs used to scale drug doses and estimate pharmacokinetic parameters when total body weight (TBW) may over- or under-represent drug distribution and clearance, especially in obesity; commonly, IBW is estimated by the Devine method and AdjBW uses a correction factor (often 0.4) applied to excess body weight for selected medications such as aminoglycosides.
https://pmc.ncbi.nlm.nih.gov/articles/PMC6782117/

IBW: A height- and sex-based estimate of “ideal” mass originally proposed for non-clinical purposes and later adopted in clinical pharmacology; the Devine equation is the most widely used in adult dosing tools and was popularized for gentamicin dosing in the 1970s.
https://www.accp.com/docs/bookstore/CCSAP/cc2020b2_sample.pdf

AdjBW: A dosing weight that adds a fraction of excess body weight (TBW − IBW) to IBW to reflect partial distribution into adipose tissue for selected drugs; a commonly used factor is 0.4, derived from aminoglycoside pharmacokinetic studies and institutional protocols, though reported factors vary by study and drug.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5662437/

Aminoglycosides and the 0.4 factor: Pharmacokinetic investigations in obese patients demonstrated that dosing purely by TBW risks overdosing due to limited distribution into adipose tissue; weight-correction methods adding about 40% of excess weight to IBW produced target concentrations in many cohorts.
https://journals.asm.org/doi/pdf/10.1128/aac.39.2.545

Ross et al. (2013) retrospective study in morbidly obese patients using extended-interval aminoglycosides found that IBW + 0.4 × (TBW − IBW) achieved target concentrations in 71% with manageable rates of sub/supratherapeutic levels, lending pragmatic support to the 0.4 factor in this context.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3760189/

Overview

When to use

Why use

Evidences

The Ideal Body Weight (IBW) represents an estimate of what a person’s weight should be based on height and gender, serving as a reference point for medical dosing and nutritional assessments. It is especially useful when actual body weight may not reflect lean mass, as in very thin or obese patients.

In contrast, Adjusted Body Weight (AdjBW) accounts for excess adipose tissue in obese individuals, preventing underdosing or overdosing of medications. Clinicians commonly apply IBW in scenarios like calculating tidal volumes for mechanical ventilation or dosing hydrophilic drugs, while AdjBW is applied for certain medications where partial consideration of excess body weight is necessary.

Using IBW and AdjBW helps tailor treatments to the patient’s physiology, balancing efficacy with safety. Together, these calculations support optimized care in critical care, anesthesia, nephrology, and general medicine, ensuring dosing accuracy and minimizing risk of adverse effects.

Overview

When to use

Why use

Evidences

Interpretation

· IBW (men): 50 + (2.3 × [height in inches – 60])

· IBW (women): 45.5 + (2.3 × [height in inches – 60])

· AdjBW: IBW + 0.4 × (Actual Body Weight – IBW)

Scenario	Weight Metric Used
Normal weight or slight overweight	IBW
Obese patients (BMI > 30)	AdjBW
Ventilator settings	IBW
Nutrition/fluids	IBW or AdjBW (context-dependent)