The aging process leads to progressive physiological changes. Individuals are more vulnerable to injury at both extremes of age. This chapter will emphasize the changes that one experiences with aging. Chronological age refers to age according to birth date, whereas biological age is the estimated age based on the degree of physiological degeneration or loss of physiologic reserve (Lee 2003). Physiologic changes do not necessarily parallel that of chronological age. Furthermore, specific physiological processes may age at different rates in the same individual. In addition to normal physiologic changes that occur with aging, coexisting medical conditions are also more prevalent in the elderly. The normal physiological changes associated with aging are distinct from changes brought on by disease. The pharmacokinetic, pharmacodynamic, neurologic, and cognitive changes in the elderly are affected as much by normal physiology as they are by disease.
Elderly patients become more sensitive to the therapeutic and toxic effects of many drugs (Vuyk 2003). The increased sensitivity has been studied for a variety of agents in a variety of settings. In general, it is important to recognize that differential sensitivity to drugs in the elderly population is a result of complex age-related changes in normal physiology, phar-macokinetics, pharmacodynamics, and organ system pathology. The rapidity and degree of these changes are influenced largely by the same factors that contribute to pathology, namely, genetics, environmental exposures, and diet. The following chapter will describe some ofthe more fundamental physiological changes to occur in the elderly population and how those changes affect basic pharmacokinetic and pharmacodynamic parameters. It will conclude with a brief discussion on the neurobiology of pain, pain assessment in the elderly, and its management.
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