The Complexity of Geriatric Pharmacology
The physiological changes that accompany aging significantly alter how medications are absorbed, distributed, metabolized, and excreted by the body. This is often referred to as altered pharmacokinetics. Additionally, pharmacodynamics—the effects drugs have on the body—also changes. Older patients may have heightened sensitivity to certain medications and may respond differently than younger patients, making a 'one-size-fits-all' approach to prescribing dangerous.
Altered Pharmacokinetics
Absorption
While the overall extent of drug absorption is not drastically changed with age, a slower gastrointestinal tract can delay the rate at which drugs are absorbed. This can affect the time it takes for a drug to reach its peak concentration in the bloodstream, potentially delaying its therapeutic effect.
Distribution
Aging is associated with a decrease in total body water and lean body mass, and an increase in body fat. This shift alters the volume of distribution for different drugs. Water-soluble drugs, like lithium, may become more concentrated in the body, while fat-soluble drugs, such as diazepam, may have a longer half-life due to increased storage in fatty tissue. Furthermore, reduced serum albumin levels, often seen in older adults, can increase the amount of free (unbound) drug in circulation for highly protein-bound medications like warfarin, raising the risk of toxicity.
Metabolism
With age, there is a reduction in liver blood flow and overall liver size. Phase I metabolism, which relies on cytochrome P450 enzymes, tends to decline, while Phase II metabolism remains relatively stable. This reduction means that drugs undergoing Phase I metabolism are cleared more slowly, increasing their risk of accumulation.
Elimination
Perhaps the most critical pharmacokinetic change is the age-related decline in renal function. Even with a normal serum creatinine level, older adults often have significantly reduced creatinine clearance. Many drugs and their active metabolites are eliminated by the kidneys, and this decline in function requires careful dosage adjustments to prevent drug accumulation and toxicity. It is recommended to use the Cockcroft-Gault equation to estimate creatinine clearance for dosage calculations in geriatric patients, rather than relying solely on estimated glomerular filtration rate (eGFR).
Pharmacodynamics Changes
Older adults often show an exaggerated or altered response to medications that affect the central nervous system, such as benzodiazepines and opioids, leading to increased sedation, confusion, and a higher risk of falls. There is also a decreased response to beta-blockers due to reduced beta-adrenergic receptor sensitivity.
Polypharmacy and Managing Comorbidities
Polypharmacy, defined as the use of multiple medications, is a widespread issue in geriatric care. This increases the risk of drug-drug and drug-disease interactions. Prescribing cascades, where a new medication is prescribed to treat the side effects of another drug, are common. Regular medication reconciliation and review are essential to identify and address these issues.
The Need for Deprescribing
Deprescribing—the planned and supervised process of discontinuing or tapering medications—is a cornerstone of safe geriatric prescribing. It is not about simply stopping drugs, but rather about re-evaluating the risk-benefit ratio of each medication in the context of the patient's current health status and goals of care. Many medications may no longer be necessary or may be causing more harm than good.
Comparison of Prescribing for Young Adults vs. Geriatric Patients
| Consideration | Young Adult Prescribing | Geriatric Patient Prescribing |
|---|---|---|
| Starting Dose | Standard dose based on clinical trials. | Typically start low and go slow; lower doses are often required. |
| Physiology | Stable organ function, minimal comorbidities. | Age-related decline in renal and hepatic function; high prevalence of comorbidities. |
| Polypharmacy | Less common, fewer drug interactions. | Very common, high risk of complex drug-drug interactions. |
| Cognition | Generally intact. | Increased risk of cognitive impairment, poor adherence. |
| Goals of Care | Often focused on disease cure or long-term management. | Individualized goals focusing on functional status, quality of life, and symptom management. |
| Monitoring | Routine follow-ups. | Frequent, vigilant monitoring for adverse effects and drug interactions. |
Functional and Cognitive Assessment
The Impact of Cognition on Adherence
Cognitive impairment is a significant factor. Memory loss, dementia, and confusion can all lead to poor medication adherence, causing either missed doses or accidental double dosing. Simplified medication regimens, pill organizers, and involving caregivers are often necessary strategies to ensure patient safety.
Frailty and Functional Status
Frailty is a syndrome of decreased physiological reserve and increased vulnerability to stressors. Frail older adults are at a higher risk of adverse drug events. Assessing a patient's functional status, including their mobility, independence, and risk of falls, should influence prescribing decisions, especially with medications known to cause sedation, orthostatic hypotension, or dizziness.
Patient-Centered Goals and Shared Decision-Making
Aligning Goals with Prescribing
What matters most to the patient should be the guiding principle. For some, maintaining a high quality of life and managing symptoms is more important than extending life. For others, aggressive management of chronic disease is paramount. Prescribing should always involve a conversation with the patient and their family or caregivers about their goals and priorities, using a shared decision-making model.
The Importance of the Patient's Voice
Patients and their caregivers are the frontline observers of a medication's effects. Encouraging them to report any new or unusual symptoms is critical, as many drug side effects can be misinterpreted as new medical conditions or part of the 'normal aging process.'
Conclusion: A Holistic Approach
In conclusion, prescribing for older adults is a complex process that demands a holistic and individualized approach. It moves beyond just treating a single disease and requires a deep understanding of age-related physiological changes, the dangers of polypharmacy, and the patient's unique circumstances, including their cognitive and functional status. By following established guidelines, focusing on deprescribing when appropriate, and engaging in shared decision-making, healthcare professionals can improve medication safety and optimize the health and quality of life for geriatric patients. A dedicated medication review at every care transition is a simple yet powerful tool for preventing medication-related harm.
One invaluable resource for guiding geriatric prescribing is the Beers Criteria, a list of potentially inappropriate medications for older adults developed by the American Geriatrics Society National Institutes of Health (NIH).
