Understand pharmacodynamics and pharmacokinetic changes related to age in older adults.
Understand the relevance of the Beers Criteria to medication administration in the aging population.
Identify the physiological changes associated with increased age related to pharmacokinetics (absorption, distribution, metabolism, and excretion) of medications.
Understand the effect of polypharmacy on the medication response of older adults.
Implement patient education about medications to prevent medication-related reactions and adverse effects.
Clinical Application Case Study
Charles Franklin is a 75-year-old African American man with a diagnosis of an enlarged prostate. He has been experiencing insomnia for the past month and has begun taking acetaminophen in the form of Tylenol PM.
KEY TERMS
Adult: person who ranges in age from 19 to 64 years
Age-related changes: physiological events due to increasing age, which affect drug responses
Older adult: person who is 65 years of age or older
Polypharmacy: use of several drugs during the same period
Risk-to-benefit ratio: poor outcome (adverse effects of medications) in relation to good outcome (desired medication effects); increases with increasing age
Introduction
Aging is a natural process that begins at birth. The most significant age-related changes begin in the adult years (19 to 64 years of age). These physiological events, which can affect drug responses, are due to increasing age. Most commonly, they occur in middle age and are related to heart disease, pulmonary insufficiency, cancer, arthritis, diabetes mellitus, obesity, substance abuse, and depression.
Older adults, people who are 65 years of age or older, are the largest consumers of health care. According to the National Institutes of Health (2010), chronic conditions have roots in the aging process. The most common health problems in older adults include arthritis, heart disease, decreased sensory perception, bone disorders, and diabetes mellitus. Older adults are also more prone to antibiotic resistant infections. The treatment of chronic illnesses and associated comorbidities results in polypharmacy, the use of multiple medications. The interactions of medications can lead to greater complications and diminished mental status. In addition, the risk-to-benefit ratio, the relationship between the negative effects and the positive effects of a medication, increases as the patient ages. The nurse and the prescriber must consider the risk of associated adverse effects of those medications as well as possible benefits these medications might have in changing physiological processes related to disease. As Howland (2009) states, older patients are more sensitive to the pharmacological effects of medication.
Pharmacodynamics in Older Adults
Pharmacodynamics involves drug actions on target cells and the resulting alterations in cellular biochemical reactions and functions. In older adults, physiological changes such as a reduced number of receptor sites for medications or affinity to receptors alter the medication’s ability to produce the desired effect. Older adults are prone to adverse drug reactions because of a decrease in the number of receptors needed for drug distribution. Beta-adrenergic agonists are less effective as a result of the decreased function of the beta-receptor system.
Cardiovascular disease is the number one cause of death in adults, including older adults. In patients with hypertension, the control of blood pressure is key to the prevention of cardiovascular disease. The administration of thiazide diuretics is the most effective treatment of hypertension in older adults (Olsen, Tindall, & Clasen, 2007). The use of digoxin (Lanoxin) in heart disease should not exceed 0.125 mg per day except when treating atrial dysrhythmias (Aschenbrenner & Venable, 2009; Fick et al., 2003). Digoxin has a low therapeutic index, placing patients at risk for adverse effects. Thus, administration of the medication with a reduced dose assists in maintaining safety.
Beers Criteria
Dr. Mark Beers initially developed the Beers Criteria list of potentially inappropriate medications used by the older adult population in 1997. Updated in 2003 (Fick et al., 2003), the list confirms that toxic medication effects and drug-related problems affect the safety of older adults and names drugs that cause problems in this population. Thirty percent of elderly hospital admissions are linked to drug reactions.
In nursing practice, it is vital to implement strategies to identify age-related changes associated with medication administration.
QSEN Safety Alert 
Drugs that produce adverse effects in older adults include
• Amiodarone (Cordarone): altered QT interval
• Amitriptyline hydrochloride: anticholinergic effects, sedation
• Cimetidine (Tagamet): confusion
• Cyclobenzaprine (Flexeril): anticholinergic effects, weakness
• Digoxin (Lanoxin): digoxin toxicity
• Diphenhydramine hydrochloride (Benadryl): urinary retention
• Flurazepam hydrochloride (Dalmane): sedation
• Hydroxyzine hydrochloride (Vistaril): confusion, sedation
• Ketorolac: gastrointestinal (GI) bleeding
• Meperidine hydrochloride (Demerol): confusion
• Methocarbamol (Robaxin): anticholinergic effects, weakness
• Methyldopa (Apo-Methyldopa; Aldomet): bradycardia, depression
• Nitrofurantoin (Macrodantin): renal toxicity
• Propoxyphene hydrochloride (Darvon): respiratory depression
Prevention of Adverse Effects
Strategies to prevent adverse drug reactions include the following:
• Assess a patient’s health history and list of medications taken by the patient, including prescription medications, over-the-counter medications, and herbal supplements.
• Assess blood urea nitrogen and creatinine clearance (CrCl) levels to determine the patient’s ability to excrete the medications.
• Assess the ratio of alanine aminotransferase to aspartate aminotransferase to determine the patient’s liver function and ability to metabolize drugs.
• Assess therapeutic drug levels as ordered by the prescriber to determine the medication effectiveness and prevention of toxicity.
• Educate the patient and family about all medications and possible drug–drug, drug–herb, and drug–diet interactions.
• Educate the patient and family about the generic and trade names of medications to prevent overmedication.
• Assess the patient’s adherence to the prescribed medications.
• Provide the patient with medication administration aids to increase adherence.
Clinical Application 5-1
What urinary effect is Mr. Franklin prone to developing since he began taking Tylenol PM?
NCLEX Success
1. When administering a beta-adrenergic agonist to a patient older than 65 years of age, what response do you anticipate?
A. The drug will work very rapidly to decrease blood pressure.
B. The dosage will need to be increased to provide an effective response.
C. The drug should be combined with atropine to enhance effectiveness.
D. The dosage will need to be titrated over 20 minutes to increase blood pressure.
2. A 75-year-old woman is having difficulty remembering to take all of her medications. Which of the following nursing interventions will assist her to improve adherence to the medication schedule?
A. Have her daughter administer the medications.
B. Decrease the number of medications administered.
C. Evaluate her ability to care for herself.
D. Provide a medication administration aid.
Pharmacokinetics in Older Adults
Aging results in physiological changes that affect the absorption, distribution, metabolism, and excretion of medications. The most relevant physiologic change is the decreased function of vital organs needed for the pharmacokinetic processes. Frail, elderly adults are at greatest risk for altered drug responses. The more physically active older adults are, the less likely they will experience altered drug responses.
Absorption
In older adults, changes in the GI tract include decreased gastric acidity, with an increase in the gastric pH, and delayed absorption or lack of absorption of medications that require this decreased pH. Other changes in the GI tract responsible for affecting drug absorption in older adults are decreased blood flow and decreased surface area to support absorption. Diminished gastric emptying also plays a role by causing the medication to be in the stomach for a longer period. This factor increases the risk of developing nausea and vomiting, thus causing elimination of the medication in emesis and promoting fluid volume deficit.
In older patients, decreased circulation means that parenteral medications are also slowly absorbed. Decreased muscle mass and altered circulation can result in abnormal blood concentrations of medications administered intramuscularly.
In all cases, a slow rate of absorption can result in changes in peak serum drug levels. This factor may require greater dosages to be administered to produce therapeutic results.
Distribution
In older adults, physiological factors that contribute to alterations in distribution of medications include diminished cardiac output, increased body fat, decreased body mass and body fluid, and decreased serum albumin. Aging results in changes in body mass changes; the proportion of body fat increases while lean body mass decreases. These changes may have the following consequences:
• Lipid-soluble drugs such as the anesthetic agents stay in the fat tissue for a longer period of time. This places older adults at risk for respiratory depression following surgery.
• The amount of body fluid decreases in proportion to total body weight. Water-soluble drugs such as antibiotics are distributed in smaller volumes due to the decrease in total body fluid volume. This increases the risk of toxicity because drug concentrations are greater.
• Many medications require serum albumin to bind, transport, and distribute the medication to the target organ. In the event that the amount of serum albumin is insufficient, the amount of free drug rises and the effect of the drug is more intense.
• Medications are not distributed adequately due to the decreased circulation and diminished cardiac output.
