Question

How does age influence the pharmacokinetic and pharmacodynmic process in the patient

Answer 1

Pharmacokinetics is best defined as what the body does to the drug; it includes

Absorption

Distribution across body compartments

Metabolism

Excretion

With aging, there are changes in all these areas; some changes are more clinically relevant. The metabolism and excretion of many drugs decrease, requiring that doses of some drugs be decreased. Toxicity may develop slowly because concentrations of chronically used drugs increase for 5 to 6 half-lives, until a steady state is achieved. For example, certain benzodiazepines (diazepam, flurazepam, chlordiazepoxide), or their active metabolites, have half-lives of up to 96 h in older patients; signs of toxicity may not appear until days or weeks after therapy is started.

Aging is characterized by progressive impairment of functional capacities of all system organs, reduction in homeostatic mechanisms, and altered response to receptor stimulation. These age-related physiologic changes influence both pharmacokinetics and pharmacodynamics of drugs in elderly patients.