Renal drug transport: a review

Renal drug elimination involves three major processes: glomerular filtration, tubular secretion, and tubular reabsorption. Drug filtration is a simple unidirectional diffusion process. Renal tubular secretion and reabsorption are bidirectional processes that often involve both passive diffusion and carrier-mediated membrane processes. Various in vivo and in vitro techniques are available to study renal drug elimination and renal drug transport. The complete renal handling of a drug is best understood from data obtained from a combination of in vivo and in vitro methodologies. At the membranes of the renal proximal tubule, a number of carrier systems are involved in the tubular secretion and/or reabsorption of various drugs. Organic acid and base transporters are two major carrier systems important in the tubular transport of a number of organic acid and base drugs, respectively. Nucleoside and P-glycoprotein transporters appear to play an important role in renal tubular transport of dideoxynucleosides (e.g., zidovudine, dideoxyinosine) and digoxin, respectively. Clinically, these transporters are not only necessary for the renal tubular secretion and reabsorption of various drugs, but are also responsible in part for the drug's pharmacologic response (e.g., furosemide), drug-drug interactions of therapeutic or toxic importance, and drug nephrotoxicity.