The Physiological Changes That Influence Medication
As the body ages, a series of natural physiological changes occur that can fundamentally alter how it handles medications. These changes, known as pharmacokinetics, involve four main processes: absorption, distribution, metabolism, and excretion. When these processes change, the drug's intended effect can be unpredictable.
Absorption
While changes in drug absorption are often minimal in healthy older adults, several factors can play a role. Age-related issues such as dysphagia (difficulty swallowing) and reduced gastrointestinal motility can alter how and when a drug is absorbed. For example, slowed gastric emptying can delay a drug's onset of action. Changes in gastric acidity, common in the elderly, can also affect the absorption of certain drugs, like some iron supplements, that require an acidic environment.
Distribution
One of the most significant age-related changes is in body composition. Older adults typically have a higher percentage of body fat and a lower percentage of total body water and lean muscle mass.
- Fat-soluble (lipophilic) drugs: These drugs, such as diazepam and chlordiazepoxide, have a larger volume of distribution due to increased body fat. This can prolong their half-life, increasing the risk of accumulation and prolonged sedative effects.
- Water-soluble (hydrophilic) drugs: These drugs, such as digoxin and lithium, have a reduced volume of distribution due to lower total body water. This can lead to higher plasma concentrations and a greater risk of toxic effects at standard doses.
- Plasma Protein Binding: Lower levels of plasma protein, particularly albumin, are common in ill or malnourished seniors. This means that for highly protein-bound drugs like phenytoin and warfarin, more of the drug remains unbound or 'free,' increasing its active concentration and the potential for toxicity.
Metabolism
The liver is the primary site of drug metabolism, and with age, liver mass and blood flow decrease. This impairs the liver's ability to metabolize drugs, particularly those that undergo first-pass metabolism. Reduced activity of certain liver enzymes (Phase I metabolism) means drugs are broken down more slowly, leading to higher drug levels and longer half-lives. Conversely, Phase II metabolism, which involves conjugation and glucuronidation, is generally less affected by age, making drugs processed this way potentially safer for seniors.
Excretion
The kidneys are responsible for clearing most drugs from the body. Renal function, measured by glomerular filtration rate (GFR), declines progressively with age. This reduced clearance capacity means that drugs and their active metabolites can accumulate, leading to increased and prolonged effects and a heightened risk of toxicity. For drugs with a narrow therapeutic index, like digoxin, this decline in renal function requires careful dose adjustment and monitoring.
The Risks of Polypharmacy and Drug Interactions
Polypharmacy, commonly defined as the use of five or more medications, is a significant and growing problem among older adults. One study found that patients on five to nine medications have a 50% chance of an adverse drug interaction.
- Drug-Drug Interactions: When multiple prescribers are involved or patients use different pharmacies, the risk of conflicting prescriptions or interactions increases. Some interactions can make a drug less effective, while others can amplify its effects, leading to dangerous consequences.
- Drug-Disease Interactions: Some medications can worsen existing conditions. For instance, certain NSAIDs can worsen heart failure or kidney disease.
- Drug-Food and Drug-Alcohol Interactions: Common foods like grapefruit can interfere with medications, and alcohol's effects are often magnified in seniors, leading to increased sedation and risk of falls.
Managing Medications Safely
Effective medication management is crucial for minimizing risks and ensuring the best therapeutic outcomes for seniors. It requires a collaborative effort between patients, caregivers, and healthcare providers.
- Maintain a Comprehensive List: Keep an up-to-date list of all prescription and over-the-counter medications, including vitamins and supplements. This list should detail the name, dosage, frequency, and reason for taking each item. Share this list with every healthcare provider.
- Use One Pharmacy: Sticking with a single pharmacy allows the pharmacist to maintain a complete record of all medications, helping to prevent potentially harmful drug interactions.
- Organize Your Medications: Using a weekly pill organizer or automated dispenser can help ensure the right dose is taken at the right time. Forgetting doses or double-dosing is a common issue, especially for those with cognitive impairment.
- Communicate with Your Doctor: Always discuss new symptoms or side effects with a healthcare professional, as they may be related to a medication. Never stop or alter a medication regimen without a doctor's guidance.
- Regular Medication Reviews: Schedule periodic reviews with your doctor or pharmacist to assess if all medications are still necessary and appropriate. This practice is known as "deprescribing" and can significantly reduce polypharmacy and its associated risks.
High-Risk Medications for Older Adults: The Beers Criteria
The American Geriatric Society maintains the Beers Criteria, a list of potentially inappropriate medications for older adults. These drugs are identified because their risks often outweigh their benefits in this population. Examples include:
- Anticholinergics: Such as some older antihistamines (diphenhydramine), can cause side effects like confusion, constipation, and urinary retention.
- Long-acting Benzodiazepines: Due to their long half-life and fat solubility, these drugs can accumulate and cause excessive sedation or delirium.
- Certain NSAIDs: Can cause gastrointestinal bleeding and kidney problems, especially with long-term use.
A Comparison of High-Risk vs. Safer Medication Choices
| Characteristic | Higher-Risk Medications for Seniors | Safer Alternatives for Seniors |
|---|---|---|
| Processing Pathway | Relies on Phase I liver enzymes (more age-sensitive) | Relies on Phase II conjugation (less age-sensitive) |
| Metabolism Time | Longer half-life due to slower metabolism and fat accumulation (e.g., long-acting benzodiazepines) | Shorter, more predictable half-life (e.g., intermediate-acting benzodiazepines) |
| Risk of Accumulation | High risk due to reduced renal excretion (e.g., Digoxin, Lithium) | Lower risk; less dependent on renal function for clearance |
| Primary Binding Site | Highly protein-bound (e.g., Warfarin, Phenytoin), sensitive to low albumin levels | Less affected by protein binding changes |
| Common Example | Diphenhydramine (Anticholinergic side effects) | Consider non-drug interventions for sleep/allergies; consult doctor for alternatives |
| Common Example | Diazepam (Long-acting benzodiazepine) | Lorazepam, Oxazepam, Temazepam (Shorter-acting, LOT drugs) |
Conclusion: Proactive Management is Key
Understanding how does old age affect medication is the first step toward safer and more effective treatment for seniors. The body's changed physiological processes require proactive and diligent medication management. By maintaining detailed records, using a single pharmacy, organizing doses, and communicating openly with healthcare professionals, seniors and their caregivers can significantly reduce the risks associated with polypharmacy and age-related changes. Ultimately, safe medication use is a cornerstone of maintaining health, independence, and quality of life in older age. For more detailed information on safe medication practices, consult authoritative resources from health organizations.
