(p. 655) Pharmacokinetics and Pharmacodynamics in Late Life 

Older patients are the major recipients of drugs, however most research during drug development is conducted in healthy younger adults. Adverse drug events are common in older adults, but are often preventable. Safe and effective drug therapy requires an understanding of both drug disposition and response in older individuals. Geriatric patients are a heterogeneous population, which is evident in the highly variable drug concentrations and differences in dose-concentration-response relationships. While there is a paucity of data regarding the age-related changes in pharmacokinetic differences in antidepressants, there is increasing evidence that the clearance of some drugs decreases with aging and therefore older patients may experience greater concentrations than younger patients at the same dose. Combined with the fact that older adults seem to be more sensitive than younger patients to adverse effects of antidepressants at lower concentrations, it is critical to control for differences in drug exposure. This chapter reviews the current data on the pharmacokinetics and pharmacodynamics of antidepressants, as well as benzodiazepines, mood stabilizers, and antipsychotics, focusing on differences in age-related changes in drug clearance and drug response, as well as side effects and drug interactions that are more prevalent in older adults.