📚 Geriatrics — L5: Drug Prescribing For The Elderly

📚 Lecture Overview

This lecture explores the specialized principles of drug prescribing for older adults, focusing on age-related physiological shifts and high vulnerability to adverse drug events. Mastering these concepts is crucial for minimizing polypharmacy, preventing prescribing cascades, and optimizing drug safety and quality of life in the geriatric population.

🎯 Key Concepts & Definitions

• Polypharmacy: The concurrent use of 5 or more drugs by a patient.
• Undertreatment: A medication therapy problem where an indication exists, but the necessary drug is not used.
• Beers Medications: Expert-consensus medications considered potentially inappropriate for older adults due to high risk versus benefit ratios.
• Prescribing Cascade: The harmful practice of using one drug to treat the adverse side effects caused by another drug.
• Unprescribing (Pruning): The intentional discontinuation of unnecessary medications to simplify regimens and reduce harm.

📖 Main Content

Geriatric Therapeutic Challenges

• Older adults face impaired physiological reserve and an age-associated loss of adaptability, leading to rapid clinical deterioration if left untreated.
• Clinical presentations are frequently atypical or cryptic, and the ability to recognize side effects is reduced.
• Patients often see multiple physicians with poor communication, raising risks for polypharmacy and therapeutic duplication.
• Common medication therapy problems include:
• Dose too high or too low
• Adverse drug reactions (ADEs) and drug-drug interactions
• Lack of adherence or compliance due to cognitive, visual, or financial barriers

Pharmacokinetics in the Elderly

• Absorption: Generally reliable, but continuous tube feedings can reduce absorption.
• Distribution: Highly altered due to body composition changes:
• Low serum albumin alters free versus bound drug proportions.
• Increased body fat increases the half-life of lipophilic drugs (e.g., Diazepam, anesthetics).
• Decreased body water is the most important change, lowering the volume of distribution ($V_d$) for polar drugs.
• Excretion (Renal): Declines due to loss of renal mass, reduced renal blood flow, and lower GFR.
• Serum creatinine is unreliable; estimation via Cockcroft-Gault is necessary.
• Drugs with predominant renal elimination require strict dose adjustments (e.g., Digoxin, Lithium, Aminoglycosides, Acyclovir).

Altered Pharmacodynamics

• Older adults exhibit changes in end-organ responsiveness at receptor and post-receptor levels.
• Increased sensitivity is seen with opiates and Warfarin, while decreased sensitivity occurs with $\beta$-blockers (e.g., Propranolol).
• Organ-specific pharmacodynamic risks:
• Urinary bladder: Anticholinergics cause urine retention.
• Eye: Anticholinergics cause blurred accommodation and acute glaucoma.
• CNS: Benzodiazepines and opiates cause sedation; $\beta$-blockers and Digoxin can trigger depression.
• Kidney: NSAIDs can precipitate acute renal failure.

High-Risk Drugs & Drug-Disease Interactions

• Adverse Drug Reactions (ADEs): ER visit rates are twice as high and hospitalization rates are seven times greater for adults $≥ 65$.
• Medications to avoid or use with extreme caution:
• Benzodiazepines (e.g., Diazepam) and Barbiturates
• NSAIDs (e.g., Indomethacin) and muscle relaxants
• Anticholinergics & Antihistamines (e.g., Diphenhydramine)
• Cardiovascular high-risk drugs: Digoxin ($>0.125/day$), Methyldopa, Reserpine, Propranolol, Warfarin
• Dangerous Drug-Disease interactions:
• CHF: Avoid Calcium Channel Blockers (CCB) and non-selective $\beta$-blockers.
• COPD/Asthma: Avoid sedative-hypnotics and $\beta$-blockers.
• Peptic Ulcer: Avoid NSAIDs and corticosteroids.
• BPH/Incontinence: Avoid anticholinergics and antihistamines.

Guidelines for Optimal Pharmacotherapy

• Start low and go slow: Begin at minimal doses and titrate gradually based on tolerability and response.
• Obtain a complete drug history, including OTC products, habits, and previous adverse reactions.
• Prescribing rules:
• Use once-daily formulations and pillboxes to aid adherence.
• Try to use one drug to treat two or more conditions.
• Avoid prescribing before a diagnosis is made.
• Utilize non-pharmacologic approaches first (e.g., Tai Chi for falls, physical therapy for arthritis).
• Educate patients and caregivers with clear, written instructions.

📊 Visual Learning

💡 Important Points to Remember

• Polypharmacy definition: Concomitant use of 5 or more medications.
• The Golden Rule: "Start low, go slow" to catch early side effects.
• Renal assessment: Serum creatinine alone is misleading; calculate clearance using Cockcroft-Gault.
• Lipophilic distribution: Increased body fat extends the half-life of drugs like Diazepam.
• De-escalation: Regularly review regimens to unprescribe drugs no longer indicated.
• Common pitfall: Never prescribe a second drug solely to mask the adverse effects of the first (avoid prescribing cascades).
• Avoid Beers criteria drugs: Keep Diphenhydramine, long-acting benzodiazepines, and indomethacin off the profile.
• Digoxin limit: Avoid doses greater than $0.125/day$ when possible.
• Heart failure trap: CCBs and non-selective $\beta$-blockers worsen congestive heart failure.
• NSAID danger: High risk for peptic ulcers, fluid retention, and acute renal failure.

⚠️ Common Exam Questions

• MCQ Trap: Examiners often test recognition of inappropriate drugs in specific disease states (e.g., prescribing a non-selective $\beta$-blocker to a patient with COPD or asthma, or giving an anticholinergic to a patient with BPH or constipation).
• Pharmacokinetic Distractor Questions: Questions may provide a serum creatinine value and ask how to adjust renal elimination drugs, tempting students to rely solely on raw creatinine rather than estimated clearance (Cockcroft-Gault).
• Prescribing Cascade Scenarios: Case studies where a patient develops a new symptom (e.g., extrapyramidal symptoms or edema) caused by drug A, and the student is asked the best next step—the correct answer is usually to stop drug A rather than adding drug B.

📝 Quick Review Checklist

I can explain the physiological changes in distribution and excretion in older adults
I understand the core principles of polypharmacy and the dangers of prescribing cascades
I can define high-risk medications and Beers criteria drugs
I know how to apply the "start low, go slow" rule and unprescribe safely
I can identify major drug-disease interactions (e.g., NSAIDs in renal failure or peptic ulcer disease)