renal clearance

Excretion of molecules (drugs, metabolites, biomolecules) in the urine by the kidney involves: 1) glomerular filtration 2) tubular secretion (active) 3) tubular resorption (passive) Glomerular filtration depends on glomerular filtration rate & protein binding. In the proximal renal tubule, anionic & cationic carrier- mediated transport occur. Organic acids are secreted by the anionic transport; organic bases are secreted by the cationic transport. These carrier systems are rather non-selective & can be bidirectional.* In the proximal & distal tubules, non-ionized weak organic acids & bases are passively resorbed (pH-dependent). The concentration gradient for passive bak-diffusion is created by resorption of H₂O with Na⁺ & other inorganic ions. * transport is predominantly secretory uric acid is bidirectionally transported

References

The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996 pg 17