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Abstract
Aging affects the pharmacokinetics and pharmacodynamics of drugs, which has potentially important implications for the use of psychotropic medication in older adults. The absorption of orally administered drugs may be impaired or delayed, the volume of distribution of most drugs is decreased, and over time, the distribution shifts toward greater drug accumulation in fat stores. Decrease in renal function with age is especially important regarding the use of lithium but is also relevant for most drugs because they are eventually cleared through the kidneys after metabolism in the liver. Because pharmacodynamic changes associated with aging will make elderly patients more sensitive to the pharmacological effects of medication-especially adverse effects-nurses should be appropriately trained in pharmacology and therapeutics in older adults.
Regulatory bodies usually consider older adults to be those older than age 65 (Hilmer, McLachlan, & Le Couteur, 2007). More than 90% of older adults take at least one medication, and the majority of them take two or more drugs (Qato et al., 2008). In the community, approximately 20% of older adults take psychotropic medication (Aparasu, Mort, & Brandt, 2003). The prevalence of psychotropic drug use is even higher in older adults who are hospitalized or who live in long-term care facilities. As people age, their bodies change, and this has potentially important implications for the use of psychotropic medication in this population. In this article, I will describe the effects of aging on the pharmacokinetics and pharmacodynamics of drugs. This information is crucial for understanding how the tolerability and safety of drugs change in older individuals and how medications should be prescribed for older patients, which will be covered in next month's article.
Drug pharmacokinetics and older adults
Pharmacokinetics refers to the absorption, distribution, metabolism, and excretion of drugs in the body. Changes can occur in these parameters with aging, which can affect how drugs are handled in older patients (Rudorfer, 1993; Turnheim, 1998).
Because of reductions in gastric acid secretion and decreased gastrointestinal blood flow, the absorption of orally administered drugs may be impaired or delayed. As a result, the oral bioavailability of drugs might be decreased in older adults, although the clinical significance of this is not well established (ElDesoky, 2007; Greenblatt, Sellers, & Shader, 1982).
Body Mass and Body...