Older adults respond to medicines differently because aging affects drug absorption, distribution, metabolism, and excretion. Diseases such as heart failure, diabetes, and kidney problems are common in the elderly, and they also use many medications at the same time (polypharmacy), increasing the risk of drug interactions and adverse drug reactions (ADRs). Safe prescribing in geriatrics requires careful drug selection, correct dosing, and regular monitoring.
PHARMACOKINETIC CHANGES IN THE ELDERLY
1. Absorption
- Reduced gastric acid secretion, GI blood flow, GI motility, pancreatic enzymes, and number of absorbing cells.
- Possible delayed drug absorption and slower onset of action.
- Vitamin and mineral deficiencies are common due to reduced active absorption.
- Passive absorption remains normal, but active absorption decreases.
2. Distribution
- Decrease in lean body mass and total body water.
- Increase in body fat → larger volume of distribution for lipid-soluble drugs.
- Lower albumin levels → higher free fraction of acidic highly protein-bound drugs (e.g., warfarin, phenytoin, diazepam).
- Risk of drug accumulation and delayed elimination in multiple dosing.
3. Metabolism
- Reduced liver cell mass and liver blood flow.
- Reduced enzyme activity (acetylation, glucuronidation).
- Slower metabolism of drugs such as propranolol, labetalol, verapamil, opioids, diazepam.
- Smoking, alcohol, diseases, or drugs like erythromycin may reduce metabolism further.
4. Excretion
- Glomerular filtration rate (GFR) decreases with age — around 30–40% loss by age 90.
- Reduced renal plasma flow and active secretion.
- Poor elimination of renally cleared drugs like digoxin, penicillins, aminoglycosides, vancomycin, lithium.
- Creatinine clearance should be calculated for proper dose adjustment.
PHARMACODYNAMIC CHANGES
- Changes in receptor numbers and sensitivity.
- Altered CNS enzyme activity.
- Reduced baroreceptor reflex → increased risk of postural hypotension.
- Reduced response to β-agonists; increased sensitivity to CNS depressants (morphine, benzodiazepines).
GENERAL PRINCIPLES OF DRUG THERAPY IN THE ELDERLY
1. Avoid unnecessary drugs
Before prescribing, ensure the drug is truly needed. Many mild conditions can be managed with lifestyle changes instead of medication.
2. Consider quality of life
Treatment should improve comfort and daily functioning, not just prolong life. In some cases, surgical intervention (e.g., hip replacement) may be better than long-term drug therapy.
3. Treat the cause, not just the symptom
Correct diagnosis is essential. Do not treat symptoms blindly without identifying the underlying illness.
4. Obtain a complete drug history
Check for allergies, previous ineffective treatments, and potential drug interactions.
5. Consider coexisting medical conditions
Elderly patients often have multiple diseases. Kidney, liver, and heart problems greatly affect drug choice and safety.
6. Choose the right drug
Select the safest effective medication while avoiding drugs that worsen existing conditions. Example: Avoid diuretics for hypertension in elderly men with prostate enlargement.
7. Dose titration
Start low and go slow. Begin with the minimum effective dose and increase gradually only if needed.
8. Choose the correct dosage form
Many elderly patients have difficulty swallowing large tablets. Use syrups, effervescent tablets, or smaller tablets when appropriate.
9. Packaging and labelling
Use easy-to-open containers and large, clear labels. Avoid blister packs if the patient has arthritis.
10. Good record keeping
Maintain updated records of all current and past medications to avoid duplication, interactions, and unnecessary treatments.
11. Regular supervision and review
Long-term prescriptions should be reviewed frequently. Elderly patients often continue medications for years without reassessment.
12. Adverse Drug Reactions (ADRs)
- Elderly patients are more prone to ADRs due to polypharmacy and age-related changes.
- Most ADRs in the elderly are dose-dependent and preventable.
- Common ADRs involve the GI system and blood-related disorders.
13. Adherence (Compliance)
Older adults can adhere well to treatment if cognitive impairment is absent and drug regimens are simple. Complicated dosing schedules reduce adherence. Tools like pill organizers and pharmacist counselling improve compliance.
Detailed Notes:
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