Drug distribution and renal excretion in the elderly.

Drug responsiveness in the elderly often differs from that in younger individuals. A causative factor is often thought to be age-related changes in the quantitative fashion in which the body handles the drug. It is speculated that changes in body size, composition, and tissue perfusion lead to differences in drug distribution. The limited supportive evidence for this is reviewed, along with the practical consequences in drug therapy. More definitive data is presented on the age-related impairment of renal function and its effects on the urinary elimination of drugs and metabolites. Methods are presented to permit rationale dosage regimen modifications for elderly patients with reduced renal function.