Drug Therapy in the Older Adult

After completing this section of the chapter, you should be able to meet the following objectives:

♦ Characterize drug therapy in the older adult population

♦ List five factors that contribute to adverse drug reactions
in the elderly

♦ Cite cautions to be used in prescribing medications for
elderly persons

Drug therapy in the older adult population is a com­plex phenomenon influenced by numerous biopsycho­social factors. The elderly population is the largest group of consumers of prescription and over-the-counter drugs. Although the older population comprises only 12.4% of the U.S. population, they consume one third of all prescription drugs and 50% of all over-the-counter medications.⁸² The incidence of adverse drug reactions in the elderly is two to three times that found in young adults. This is considered to be a conservative estimate because drug reactions are less well recognized in older adults and reactions often can mimic symptoms of specific disease states.

Errors in the administration of medications and com­pliance are common among the older adult population, estimated by several authorities to be between 25% and 50% for community-dwelling elderly persons. Reasons for this high volume of errors are numerous. Poor manual dexterity, failing eyesight, lack of understanding about the treatment regimen, attitudes and beliefs about medication use, mistrust of health care providers, and forgetfulness or confusion are but a few factors that can affect the adher­ence to medication regimens. The role of the health care provider also can contribute to improper medication use. There can be a tendency to treat symptoms with drugs rather than fully investigate the cause of those symptoms. To compound matters, accurate diagnosis of specific dis­ease states can be difficult because older adults tend to

underreport symptoms and because presenting symptoms are often atypical.^82,83

Age-related physiologic changes also account for ad­verse effects of medications. In general, the absorption of orally ingested drugs remains essentially unchanged with age, even though the gastric pH is known to rise and gastric emptying time can be delayed. Changes in drug distribu­tion, however, are clinically significant. Because lean body mass and total body water decrease with advancing age, water-soluble drugs such as digoxin and propranolol tend to have a smaller volume of distribution, resulting in higher plasma concentrations for a given dose and increased like­lihood of a toxic reaction. Conversely, fat-soluble drugs such as diazepam are more widely distributed and accumu­late in fatty tissue owing to an increase in adipose tissue with aging. This can cause a delay in elimination and accu­mulation of the drug over time (i.e., prolonged half-life) with multiple doses of the same drug. Drug metabolism through the liver is thought to be altered owing to the de­crease in hepatic blood flow seen in the older adult. Renal excretion controls the elimination of drugs from the body, and because kidney function declines with age, the rate of drug excretion decreases. This can result in an increased half-life of drugs and is why estimates of creatinine clear­ance are recommended to determine drug dosing.⁸⁴,⁸⁵

Drug use for older adults warrants a cautious approach. "Start low and go slow" is the adage governing drug pre­scribing in geriatric pharmacology. Older adults often can achieve therapeutic results on small doses of medications. If necessary, dosing can then be titrated slowly according to response.

Further complicating matters is the issue of polyphar-macy in older adults, who often have multiple disorders that may require multiple drug therapies. Polypharmacy increases the risk for drug interactions and adverse drug reactions and decreases compliance. Drugs and disease states also can interact, causing adverse effects. For exam­ple, psychotropic drugs administered to older adults with dementia may cause a worsening of confusion; β-blocking agents administered to an individual with chronic ob­structive pulmonary disease may induce bronchoconstric-tion; and nonsteroidal anti-inflammatory medications given to an older adult with hypertension can raise blood pressure further.

The use of certain types of medications carries a high risk for older adults and should be avoided if possible. In general, long-acting drugs or drugs with prolonged half-lives can be problematic. Many sedatives and hypnotics fit into this category, and drugs such as diazepam and flur-azepam should be avoided. Other classes of drugs, such as antidepressants and anxiolytics, may provide the nec­essary symptomatic relief and may be more appropriate for older adults than sedatives and hypnotics. Use of these agents warrants caution, however, with consideration for the unique pharmacokinetic changes that accompany aging. Drugs that possess anticholinergic properties should also be used with caution. Anticholinergics are used for a va­riety of conditions; however, side effects such as dry mouth and eyes, blurred vision, and constipation are common. These drugs can also cause more serious side effects, such as confusion, urinary retention, and orthostatic hypotension.

Agents that enter the central nervous system, including nar­cotics and alcohol, can cause a variety of problems, most no­tably delirium. These problems most likely occur as a result of a decreased central nervous system reserve capacity.⁸⁵,⁸⁶

Because of the serious implications of medication use in the elderly, strategies need to be used to enhance thera­peutic effects and prevent harm. Careful evaluation of the need for the medication by the health care provider is the first step. Once decided, analysis of the individual's current medication regimen and disease states is necessary to prevent drug-drug interactions, drug-disease interactions, and adverse responses. Dosing should be at the low end, and frequency of drug administration should be kept to a minimum to simplify the routine and enhance compli­ance. Timing the dose to a specific activity of daily living (e.g., "take with breakfast") can also improve compliance, as can special packaging devices such as pill boxes and blis­ter packs. The cost of medications is another important fac­tor for older adults on reduced, fixed incomes. Choosing less expensive products of equal efficacy can increase com­pliance. The importance of educating the individual about the medication cannot be overemphasized. Health care pro­fessionals need to provide verbal and written information on the principles of medication use and on the specific medications being used. This facilitates active, involved participation by the older adult and enhances the individ­ual's ability to make informed decisions.

In summary, drug therapy in the older adult population is a complex phenomenon influenced by numerous biopsycho-social factors. Alterations in pharmacokinetics occur with ad­vancing age and increase the likelihood of toxic reactions. ^“Start low and go slow" is the adage governing geriatric phar­macology. Centrally acting drugs and drugs with long half-lives should be avoided when possible. Drug-drug interactions, drug-disease interactions, and adverse reactions increase in the elderly population. Educating the older adult about drug use is an important factor in ensuring compliance and accurate medication administration.

 

REVIEW EXERCISES

It is said that the aging body can accomplish most, if not all, of the functions of its youth; the difference is that they may take longer, require greater motivation, and be less precise.

A. Explain how this concept might contribute to falls in elderly persons.

Nocturia or the need to urinate during the night is a common problem of the elderly.

A. Explain the rationale for this complaint.

Errors and adverse drug reactions are a continual threat for the elderly.

A. Explain common causes of inappropriate medica­tion use in the elderly.