Clearance (Cl) Blood flow (Q) 7 Extraction Ratio (ER)
- Volume of blood per unit time (e.g. L/min) from which chemical is completely extracted. The higher the clearance, the smaller the half-life.
- Blood flow is allometrically scalable across mammalian species
- Extraction can occur by diffusion mechanism (e.g., glomerular filtration in the kidney) or by metabolic mechanism (e.g., liver).
- Clearance can be flow-limited (high ER) or capacity limited (low ER). Flow-limited clearance across species is more likely to be scalable than capacity-limited clearance