In pediatric pharmacokinetics, clearance is commonly adjusted using allometric scaling with body weight. What does allometric scaling use?

• A. A power-law relationship between clearance and body weight
• B. An linear relationship with age
• C. A fixed multiplier regardless of weight
• D. Only BMI

Answer: (A)

Allometric scaling uses a power-law relationship between clearance and body weight. In practice, clearance is modeled as CL = CL_ref × (WT / WT_ref)^b, with an exponent b typically around 0.75 for clearance. This non-linear scaling reflects how physiological processes like organ size and blood flow don’t increase in direct proportion to weight. For example, doubling body weight increases clearance by about 2^0.75 ≈ 1.68, not by a factor of 2. BMI or age alone don’t capture this size-dependent change as effectively as the weight-based power law does. In pediatrics, this approach helps predict how clearance changes across a wide range of weights, guiding appropriate dosing.