Understanding the Physiologic Considerations That Must Be Taken Into Account When Medicating Elders

According to the FDA, older adults are more likely to experience adverse drug reactions due to age-related changes affecting medication usage. When medicating elders, healthcare providers and caregivers must consider these significant physiologic considerations to ensure treatment is both safe and effective.

Quick Summary

The physiological changes that must be taken into account when medicating elders include altered pharmacokinetics (absorption, distribution, metabolism, excretion), modified pharmacodynamics (receptor sensitivity), and the increased prevalence of polypharmacy and comorbidities.

Key Points

• Altered Pharmacokinetics: Aging changes how the body absorbs, distributes, metabolizes, and excretes drugs, often requiring lower doses and closer monitoring.

• Increased Drug Sensitivity: Elders are more sensitive to the effects of many medications, especially those affecting the central nervous and cardiovascular systems.

• Polypharmacy Risk: Taking multiple medications significantly increases the risk of dangerous drug-drug interactions and adverse side effects, common in older adults with multiple conditions.

• Medication Adherence Challenges: Factors like complex regimens, cognitive decline, and cost can lead to poor adherence, compromising treatment effectiveness.

• Renal Function Misinterpretation: Standard lab tests for kidney function can be unreliable in elders, necessitating a careful assessment of true renal clearance to prevent drug accumulation.

• Increased Adverse Event Risk: Physiological changes and comorbidities make elders highly susceptible to adverse drug reactions, which are a major cause of hospitalization.

The Importance of Geriatric Pharmacology

Medicating elders is a nuanced process that goes far beyond simply adjusting dosages based on weight. The aging body undergoes a series of complex and often gradual physiological transformations that can dramatically alter how medications are processed and affect an individual. A thorough understanding of these changes is essential for preventing adverse drug events, which are a major cause of hospitalization in older adults. Safe medication management requires a holistic approach, considering not just the medication itself, but the entire context of the elder's health, lifestyle, and other concurrent treatments.

Pharmacokinetic Changes in the Elderly

Pharmacokinetics describes how the body affects a drug. The acronym ADME—Absorption, Distribution, Metabolism, and Excretion—provides a framework for understanding these changes in elders.

Alterations in Drug Absorption

While absorption is generally thought to be less affected by age than other processes, some factors can influence it:

• Gastric pH: Older adults often have reduced gastric acid production (achlorhydria), which can affect the absorption of certain medications that require an acidic environment, such as iron or some antifungal drugs.
• Gastric Motility: Slowed gastric emptying can delay the rate at which a drug is absorbed. While this may not significantly alter the total amount absorbed, it can delay the drug's onset of action.
• Splanchnic Blood Flow: A slight reduction in blood flow to the digestive system can modestly decrease the rate of absorption for some drugs.

Changes in Drug Distribution

An elder's body composition differs significantly from a younger person's, impacting how drugs are distributed:

• Decreased Total Body Water: Less body water means water-soluble drugs (like lithium or digoxin) are distributed in a smaller volume. This can lead to higher plasma concentrations and an increased risk of toxicity if dosages are not adjusted.
• Increased Body Fat: Conversely, an increase in body fat percentage provides a larger reservoir for fat-soluble drugs (like diazepam). This can lead to a prolonged elimination half-life, meaning the drug stays in the body longer and can have residual effects.
• Reduced Serum Albumin: Albumin levels can decrease with age, particularly in those with malnutrition. Many drugs bind to albumin, so lower levels mean a higher proportion of the drug remains unbound or "free" in the bloodstream, increasing its pharmacological effect and potential toxicity.

Modified Drug Metabolism

The liver's ability to metabolize drugs often decreases with age:

• Reduced Hepatic Blood Flow: The liver's blood flow diminishes, which affects the clearance of drugs with a high first-pass metabolism, such as propranolol.
• Decreased Liver Mass and Enzyme Activity: The size of the liver and the activity of certain enzymes, particularly the cytochrome P450 (CYP450) system, can decrease. This can reduce the rate at which some drugs are broken down, prolonging their effects.

Impaired Drug Excretion

Renal function is a critical component of drug elimination and almost universally declines with age:

• Decreased Renal Function: The kidneys' filtering capacity (glomerular filtration rate) decreases over time. This can cause drugs primarily eliminated through the kidneys (like many antibiotics and certain cardiovascular drugs) to accumulate in the body, leading to toxicity.
• Unreliable Indicators: The standard lab test for kidney function, serum creatinine, can be misleading in elders because reduced muscle mass leads to less creatinine production. Therefore, a creatinine level that appears normal may not accurately reflect the true extent of renal impairment.

Pharmacodynamic Changes

Pharmacodynamics refers to how a drug affects the body. In elders, the body's response to a drug can be altered independently of its concentration in the plasma.

Altered Receptor Sensitivity

• Increased Sensitivity: Many elders exhibit increased sensitivity to certain drug classes, including psychotropics (like benzodiazepines), opioids, and anticoagulants. This is often due to changes in receptor numbers or affinity, or a decline in homeostatic reserve.
• Decreased Baroreceptor Sensitivity: Baroreceptors help regulate blood pressure. Their reduced sensitivity in older adults makes them more susceptible to orthostatic hypotension (a drop in blood pressure when standing) from cardiovascular medications.
• Increased Central Nervous System (CNS) Sensitivity: Elders are more vulnerable to CNS side effects, such as confusion, delirium, and sedation, from medications that cross the blood-brain barrier.

The Risks of Polypharmacy

Polypharmacy, the use of multiple medications, is a significant concern in geriatric care. When elders take five or more drugs concurrently, the risk of adverse drug interactions and side effects escalates dramatically.

The Vicious Cycle of Polypharmacy

1. Cascading Prescribing: A new drug is prescribed to treat a side effect of another drug. For example, a medication causes insomnia, so a new drug is prescribed for sleep.
2. Increased Drug-Drug Interactions: The more medications in a regimen, the higher the chance of one drug altering the effect or metabolism of another.
3. Worsening Health Outcomes: Polypharmacy is linked to a higher risk of falls, functional decline, cognitive impairment, and hospitalization.

Polypharmacy Risk Comparison

Feature	Low-Risk Scenario (Single Medication)	High-Risk Scenario (Polypharmacy)
Drug Interactions	Minimal risk of interaction.	Substantial risk of dangerous interactions.
Side Effects	Side effects typically predictable and isolated.	Side effects are complex, synergistic, and hard to attribute.
Adherence	High likelihood of adherence due to simple schedule.	Lower adherence due to confusion and complexity of regimen.
Monitoring	Straightforward monitoring for a single drug's efficacy and toxicity.	Requires intensive monitoring for multiple drug effects and potential drug-drug interactions.
Cognitive Load	Minimal cognitive burden for the patient.	High cognitive load, potentially overwhelming for patients with cognitive decline.

Factors Affecting Medication Adherence

Non-adherence to medication regimens is a common issue in the elderly population. It can be caused by a variety of factors:

1. Complexity of the Regimen: Multi-drug, multi-dose schedules are difficult to follow correctly.
2. Cognitive Impairment: Dementia or other forms of cognitive decline can make it challenging to remember to take medications.
3. Sensory and Motor Deficits: Poor eyesight, hearing loss, or arthritis can interfere with reading labels, opening bottles, or administering injections.
4. Financial Constraints: High medication costs can lead patients to skip or ration doses.
5. Lack of Understanding: Low health literacy can result in a misunderstanding of a medication's purpose or potential side effects.

Strategies for Safe Geriatric Prescribing

Healthcare providers employ several strategies to mitigate the risks associated with medicating elders:

• Start Low, Go Slow: The principle of starting with the lowest effective dose and titrating slowly is paramount in geriatric pharmacotherapy.
• Medication Reconciliation: Thoroughly review a patient's complete medication list, including over-the-counter drugs and supplements, at every encounter to identify and eliminate unnecessary or potentially harmful medications.
• Use the Beers Criteria: This tool, developed by the American Geriatrics Society, lists medications potentially inappropriate for use in older adults.
• Educate and Involve: Ensure patients and their caregivers understand the purpose, dosage, and side effects of each medication. Encourage them to use tools like pillboxes to simplify complex schedules.
• Non-Pharmacological Alternatives: Consider non-drug therapies where appropriate, particularly for conditions like insomnia or anxiety. For authoritative guidelines on geriatric care, resources like those from the American Geriatrics Society are invaluable.

Conclusion

Medicating elders demands a thoughtful, individualized approach that acknowledges the profound physiological changes of aging. From altered pharmacokinetics and pharmacodynamics to the significant risks of polypharmacy, numerous factors require careful consideration. By adopting best practices like starting low and going slow, performing regular medication reviews, and prioritizing patient education, healthcare providers can help ensure that older adults receive effective treatment while minimizing the risks of adverse drug events. This comprehensive strategy is vital for promoting healthy aging and improving the quality of life for seniors.

Frequently Asked Questions

Why are elders more susceptible to drug side effects?

Elders are more susceptible to drug side effects due to age-related changes in their body's composition, reduced organ function (liver and kidneys), and increased sensitivity of drug receptors in the body and brain.

What is polypharmacy and why is it a concern when medicating elders?

Polypharmacy is the use of multiple medications, typically five or more. It is a significant concern because it dramatically increases the risk of drug-drug interactions, adverse side effects, and issues with medication adherence.

How does aging affect the metabolism of medications?

Aging often leads to a decrease in liver size, blood flow, and the activity of metabolic enzymes. This can slow down the breakdown of medications, causing them to stay in the body longer and increasing the risk of accumulation and toxicity.

Why is 'start low, go slow' a key principle for medicating elders?

The 'start low, go slow' principle is crucial because an elder's altered physiology means a standard dose could be too potent. Starting with a lower dose and increasing it gradually allows the clinician to gauge the patient's response and minimize adverse effects.

What role does reduced kidney function play in medication management for elders?

Reduced kidney function impairs the body's ability to excrete drugs, particularly water-soluble ones. This can lead to drug accumulation and toxicity, requiring dosage adjustments and close monitoring of renal function, which can be difficult to assess accurately in older adults.

Can cognitive changes affect how elders take their medication?

Yes, cognitive changes are a major factor. Mild to moderate cognitive impairment can make it difficult for elders to remember complex medication schedules, understand instructions, or recognize and report side effects, leading to poor adherence.

How can caregivers help improve medication safety for elders?

Caregivers can help by creating a clear, simple medication schedule, using pillboxes, maintaining an updated list of all medications and supplements, accompanying the elder to appointments, and communicating any concerns or observed side effects to the healthcare provider.