Adjusted Body Weight

Adjusted body weight accounts for the fact that adipose tissue is not as metabolically active or vascularized as lean body mass. The 0.4 (40%) correction factor estimates the additional volume of distribution and metabolic demand contributed by excess adipose tissue without assuming it behaves like muscle or organ tissue.

Adjusted Body Weight emerged from clinical pharmacy research in the late 1970s and early 80s. Clinicians observed that dosing based on Actual Body Weight led to toxic levels of hydrophilic drugs, while dosing on Ideal Body Weight resulted in treatment failure. The "40% rule" was the mathematical compromise that best fit observed serum concentrations.