Using allometric scaling with BW^0.75, estimate human CL for a 70 kg person given a 10 kg animal with CL = 3 L/h.

• A. 6.5 L/h
• B. 9.8 L/h
• C. 24.2 L/h
• D. 12.9 L/h

Answer: (D)

Allometric scaling of clearance uses body weight raised to the 0.75 power to account for size differences in how drugs are cleared across species. The human clearance is estimated from an animal value by multiplying by the weight ratio to the 0.75 power: CL_human = CL_animal × (BW_human / BW_animal)^0.75.

Here, CL_animal is 3 L/h from a 10 kg animal, and you’re scaling to a 70 kg human. So CL_human ≈ 3 × (70/10)^0.75 = 3 × 7^0.75. Calculating 7^0.75 gives about 4.3, so CL_human ≈ 3 × 4.3 ≈ 12.9 L/h.

Thus the estimated human clearance is about 12.9 L/h. Using different exponents would yield other numbers (e.g., 7^1 would give 21 L/h), but 0.75 is the standard exponent used for clearance scaling.