Renal Elimination

Renal drug elimination is the net result of three processes: renal excretion = glomerular filtration + tubular secretion − tubular reabsorption Glomerular filtration is passive and applies primarily to the unbound fraction of a drug. A drug that is highly protein-bound has less free drug available to cross the glomerular filter. Tubular secretion occurs mainly in the proximal tubule and is transporter-mediated; it can move both unbound and protein-bound drug into the tubular lumen. Tubular reabsorption returns some drug from the lumen to the bloodstream, reducing net excretion. This distinction explains why a falling GFR does not affect every drug in the same way. A drug that depends mainly on filtration will accumulate as filtration falls. A drug that relies substantially on secretion may accumulate because transporter capacity is reduced or because another medication competes for the same transporter. A drug that is readily reabsorbed may remain in the body longer even when it has been filtered normally. The major proximal tubular transporter families are: - Organic anion transporters (OATs): handle many anionic or acidic drugs. - Organic cation transporters...