Geriatric Pharmacology and Clinical Pharmacology for Physical Therapists Notes
Overview of Geriatric Pharmacology
Foundational Source: These notes are based on the geriatric pharmacology chapter in Geriatric Physical Therapy by Guccione, Wong, and Avers.
Primary Focus: The study of how pharmacological agents specifically affect the geriatric population, focusing on physiological changes and unique challenges inherent to aging individuals.
Major Issues in Geriatric Pharmacology
There are two overarching concerns when managing medications in older adults: polypharmacy and altered drug responses.
Polypharmacy
Definition: The use of multiple medications concurrently, including both prescription drugs and over-the-counter (OTC) products.
Medication Cascade Effect: A phenomenon where a patient is prescribed a new medication to treat the side effects of an existing medication.
Example: A patient takes a glucocorticoid (steroid) for inflammation. This leads to osteoporosis, requiring a bisphosphonate. The steroid may also impair blood glucose levels, necessitating additional medication for glycemic control. This creates a cycle of increasing medication requirements to counteract previous ones.
Drug-Drug Interactions: The risk of interactions increases exponentially with the number of medications.
Canceling Effects: One drug may oppose the mechanism of another. For example, medications for Alzheimer’s disease and medications for urinary incontinence both target acetylcholine; one increases it while the other decreases it.
Excessive Side Effects: Multiple drugs may have additive effects. Chronic Heart Failure (CHF) patients often take beta-blockers, ACE inhibitors, and diuretics simultaneously. While each targets the heart or sympathetic nervous system, the combined effect can cause severe hypotension, leading to dizziness, high fall risk, and the need for medication adjustments.
Decreased Adherence: High pill counts lead to lower compliance for several reasons:
Cognitive Issues: Difficulty remembering complex schedules and timings for various medications.
Financial Burden: High costs may force patients to choose which medications to purchase based on monthly affordability.
Lack of Perceived Benefit: Patients are less likely to adhere to medications for "silent killers" like hypertension or CHF because they do not feel an immediate symptom relief as they do with pain medication.
Altered Response to Drugs
Pharmacokinetic Changes (How the body handles the drug):
Absorption: This is often the least significant factor because physiological changes may offset each other. For instance, decreased blood flow to the gut is countered by decreased GI motility.
Distribution: Influenced by changes in body weight, total body water, lean body mass, and body fat.
Water-Soluble Drugs: Medications like morphine become more concentrated when total body water decreases.
Lipid-Soluble Drugs: Increased body fat levels cause lipid-soluble drugs (e.g., general anesthetics) to be stored longer in the system.
Metabolism: Occurs primarily in the liver. A decreased ability to metabolize drugs is one of the most significant changes in aging.
Excretion: One of the most important factors. Decreased renal clearance leads to a longer drug half-life, significantly increasing the risk of toxicity.
Pharmacodynamic Changes (How the drug affects the body):
Refers to physiological changes in homeostatic mechanisms, vascular compliance, and sensitivity to baroreceptors.
Receptor Affinity: Certain tissues show altered sensitivity. The Central Nervous System (CNS) often shows increased sensitivity to opioids, whereas the cardiovascular system may show decreased sensitivity to beta-adrenergic agonists.
Factors Increasing Adverse Drug Reactions (ADRs)
Multiple Disease States: Comorbidities involving the liver and kidneys directly impair drug metabolism and excretion.
Lack of Proper Drug Testing: Many clinical trials do not historically include participants aged and older. Regulation is shifting toward requiring trials to include older subjects to ensure safety and efficacy in this demographic.
Patient Education and Non-Adherence: Issues include physical inability to open containers or visual impairments that prevent seeing labels or pill characteristics.
Beers List / Beers Criteria: Established in by Dr. Mark Beers, this is a dictionary of potentially inappropriate medications for adults over .
Benzodiazepines: These are often avoided due to a link with Alzheimer’s-like symptoms or falls. Alternatives like beta-blockers may be preferred for managing anxiety.
Dietary Factors: Poor diet contributes to ADRs. Some medications deplete nutrients like magnesium.
Substance Use: Smoking and alcohol consumption can interfere with drug efficacy and increase side effects.
Common Adverse Drug Reactions in Older Adults
GI Issues: Common across many drug classes; constipation is particularly prevalent due to decreased mobility.
Sedation: Creates a significant risk for falls.
Confusion: Can be a side effect of medications such as Lithium or Digitalis (digoxin). It can be difficult to distinguish if confusion is a drug side effect, a symptom of an underlying condition (like a UTI), or the onset of dementia.
Depression: Can be exacerbated by antipsychotics or certain antihypertensives like Propranolol.
Orthostatic Hypotension: Common with cardiovascular drugs; results in dizziness upon standing and increased fracture risk from falls.
Fatigue and Weakness: Often caused by diuretics or muscle relaxants.
Dizziness and Falls: May be drug-induced or caused by new disorders like Benign Paroxysmal Positional Vertigo (BPPV).
Anticholinergic Effects: Seen with antihistamines, antidepressants, and some antipsychotics. Symptoms include dry mouth, blurred vision, constipation, urinary retention, drowsiness, and confusion.
Extrapyramidal Symptoms: Motor side effects like Tardive Dyskinesia, particularly from antipsychotics.
Clinical Warning: Tardive Dyskinesia can become irreversible; therapists must report motor changes to a physician immediately.
Chemical vs. Physical Restraints
Physical Restraints: Items like bed rails or seatbelts on wheelchairs used to limit movement.
Chemical Restraints: The use of antipsychotic medications to manage behavioral symptoms (like agitation in Alzheimer’s) to minimize the need for close supervision. This is highly regulated to prevent the misuse of medications purely for the convenience of staff.
Drug Classes and Considerations for Older Adults
Psychotropic Medications
Sedative-Hypnotics / Anti-anxiety: Primarily benzodiazepines.
Hangover Effect: Residual drugs in the system the following morning increase fall risk.
Anterograde Amnesia: Difficulty forming new memories while on the drug.
Rebound Effect: Increased symptoms of insomnia or anxiety for several days after sudden cessation.
Bipolar Medications: Predominantly Lithium.
Toxicity Signs: Metallic taste, tremors, muscular weakness, and fatigue.
Neurological and Pain Medications
Antipsychotics: Used for hallucinations or agitation in Alzheimer’s. Newer agents have less risk of extrapyramidal symptoms, but sedation and orthostatic hypotension remain concerns.
Parkinson’s Meds: Levodopa/Carbidopa is the gold standard. Effectiveness often wears off after to years.
On/Off Phenomenon: Fluctuations in motor control, including akinesia (freezing) at the end of a dose.
Seizure Medications: Often prescribed due to strokes, tumors, or degenerative brain diseases. Sedation is the primary side effect.
Pain/Inflammation:
Opioids: Concerns include constipation, sedation, and respiratory depression (must monitor vitals).
NSAIDs: Primary risk is gastric irritation or ulcers due to increased sensitivity.
Cardiovascular Medications
Hypertension: Goal blood pressure is often higher in the elderly (e.g., to ) compared to younger adults ( to ) to prevent orthostatic hypotension and syncope.
Congestive Heart Failure:
Reduce Workload: ACE inhibitors, beta-blockers.
Increase Pumping: Digitalis, ARNis.
Angina: Treated with beta-blockers or calcium channel blockers. Acute attacks use Nitroglycerin, which causes peripheral vasodilation, headaches, and significant blood pressure drops.
Hyperlipidemia: Treated with Statins.
Side Effect: Myopathy (muscle pain and weakness) occurs in a significant percentage of patients.
Coagulation Disorders: Anticoagulants (Heparin, Warfarin) increase hemorrhage risk.
Clinical Insight: Mild falls without loss of consciousness can lead to slow brain bleeds in patients on blood thinners. Patients should be evaluated after any head strike regardless of severity.
Respiratory and GI Medications
Respiratory:
Antitussives: May contain opioids; over-suppression of cough can prevent necessary lung clearance.
Beta-1 Cross-reactivity: Oral asthma/COPD meds can cause tachycardia, whereas inhaled forms have fewer systemic effects.
GI: Proton Pump Inhibitors (PPIs) are linked to decreased magnesium levels, increased fracture risk, and a propensity toward Alzheimer’s symptoms.
Hormonal Agents
Estrogen Replacement (Post-menopause):
Pros: Protects bones (osteoporosis) and heart; potentially improves cognition.
Cons: Increases risk of stroke, blood clots, breast cancer, and endometrial cancer.
SERMs: Selective Estrogen Receptor Modulators target bones and heart while blocking receptors in breast/uterine tissue.
Androgen Replacement (Men):
Pros: Increases lean body mass, energy, and libido.
Cons: Increases risk of prostate cancer.
Infections and Cancer
Infections: Antibacterials (Fluoroquinolones like Cipro) increase the risk of tendon rupture, particularly the Achilles tendon.
Vaccines: Highly emphasized (flu, pneumonia) because older adults do not tolerate antivirals well.
Cancer Drugs: Side effects are often tolerated because the benefits (inhibiting DNA/RNA replication of cancer cells) outweigh the toxicity to the heart and nervous system (e.g., anemia).
General Strategies for Physical Therapy
Differential Diagnosis: Determine if symptoms are musculoskeletal, visceral, or medication side effects.
Scheduling: Coordinate therapy with peak drug dosages.
Parkinson’s: See the patient to after Levodopa/Carbidopa for peak performance.
Asthma: Use nebulizers or inhalers prior to exercise.
Avoiding Harmful Interactions:
Do not exercise a limb immediately after an insulin injection in that specific limb (increased absorption rate).
Avoid placing hot packs over transdermal drug patches (increases systemic absorption).
Be cautious with whirlpools for patients on vasodilators to avoid systemic hypotension.
Education and Compliance: PTs spend more time with patients than doctors and should encourage adherence, identify normal vs. abnormal side effects, and educate on the importance of managing "silent" conditions like hypertension.