Pharmacokinetics in renal failure.

A knowledge of pharmacokinetic principles is essential to understand dosage modification for drugs used in patients in renal failure. Dosage modification is indicated either where drugs have a low therapeutic index, or where renal mechanisms play a major role in drug elimination. Drug renal clearance can be indexed to creatinine clearance in order to gauge the degree of drug elimination impairment. Two schemes of dosage modification have been proposed; dosage interval extension or dosage size reduction. In addition to effects on drug elimination, renal failure may also alter drug absorption, distribution, protein binding and metabolism. Dialysis regimens, by eliminating drugs to a greater or lesser degree, have implications for drug therapy.