Drug monitoring in the elderly.

Although the gut changes markedly with age no important differences in drug absorption have yet been demonstrated for any of a wide variety of drugs. Alterations in body structure and function can have important consequences on drug distribution in the elderly. There is a considerable reduction in total body mass with age and the proportion of lean body tissue decreases while there is a relative increase in the amount of adipose tissue. Protein binding of drugs can also be affected by age. Acidic drugs may be bound less in many older patients, mainly because of a general decrease in plasma albumin concentrations. Alpha-1-acid glycoprotein is of importance in the binding of basic drugs and its elevation in the elderly suggests that it may have an important effect on free drug concentration. Drug metabolism generally involves oxidative and conjugative reactions by the hepatic microsomal enzymes. There is little change in conjugative capacity with age although some oxidative pathways have been shown to be impaired. The steady decline in glomerular and tubular function with age is reflected in corresponding decreases in drug elimination for those drugs removed by this route.