Table 2

Some size descriptors used for determining doses in obese patients

Body size descriptor	Formula	Comment
Body mass index (BMI), kg/m²	Total body weight (TBW)/height (m)²	Fails to distinguish between adipose tissue and lean muscle mass, or sexes
Body surface area (BSA), m²	Haycock:	Commonly used in oncology to determine doses of cytotoxics
	0.024265×height (cm)^0.3964×TBW (kg)^0.5378
	Boyd: 4.688×TBW^{(0.8168–0.0154×log TBW)}	Does not distinguish between sexes
Mostellar: ((TBW×height (cm))/3600)^½
Ideal body weight (IBW), kg	Various methods41:	Accounts for sex, but not body composition
	BMI
	Moore
	McLaren
Adjusted body weight (ABW), kg	IBW+factor×(TBW−IBW)	Attempts to adjust for body composition
Adjusted body weight (ABW), kg	IBW+factor×(TBW−IBW)	Often used for calculating doses of aminoglycosides
Lean body weight (LBW), kg^*	James' equation42: 1.10×TBW−0.0128×BMI×TBW (males) 1.07×TBW−0.0148×BMI×TBW (females)	Closely related to lean (fat-free) mass and corresponds to extracellular fluid, muscle, bone, vital organs
Lean body weight (LBW), kg^*	Semi-mechanistic model43: (9270×TBW)/(A+B×BMI), where A and B are: 6680 and 216, respectively (males), 8780 and 244, respectively (females)
Predicted normal weight (PNW), kg^*	1.57×TBW−0.0183×BMI×TBW−10.5 (males)	Predicts the normal weight of an obese individual. Accuracy may diminish at extremes of height and weight
Predicted normal weight (PNW), kg^*	1.75×TBW−0.0242×BMI×TBW−12.6 (females)

↵* These body size descriptors have been developed from adolescent and adult subjects and have not been formally validated for children.