Drug Sensitivity in Older Adults: The Role of Physiologic and Pharmacokinetic Factors

Age-related changes in physiology and pharmacokinetics (how drugs are used in the body) lead to increased drug sensitivity and potentially harmful drug effects. This report addresses the heightened sensitivity to drug effects seen in older adults. The first section of the report presents three examples of physiologic decline: a) decreased plasma protein binding affects drug distribution, b) declining liver function affects drug metabolism, and c) impaired kidney function delays drug elimination. The next section illustrates by example the risks associated with altered physiology: a) decline in plasma protein binding may result in an intensified effect of the drug Phenytoin, b) altered liver function increases the sedative effects of Diazepam, and c) declining kidney function results in accumulation of the drug Gentamicin, where toxic effects include kidney failure and deafness. The last section is a discussion of some broad considerations for geriatric pharmacology. Adverse drug reactions can largely be avoided by carefully weighing the needs and clinical status of older persons on an individual basis both prior to and throughout the course of a given drug therapy.