Pharmacology Essentials: Systems and Drug Actions

Posted on Feb 21, 2025 in Medicine & Health

Introduction to Pharmacology

Pharmacology is the branch of medical science that studies drugs, their actions, interactions, and effects on the human body. It is divided into two main areas:

1. Pharmacokinetics – How the body affects a drug (absorption, distribution, metabolism, and excretion).
2. Pharmacodynamics – How a drug affects the body (mechanism of action, therapeutic effects, and side effects).

Pharmacokinetics (ADME Process)

1. Absorption – How a drug enters the bloodstream (e.g., oral, intravenous, intramuscular).
2. Distribution – How the drug spreads through body tissues and fluids.
3. Metabolism – How the drug is broken down (mainly in the liver).
4. Excretion – How the drug is eliminated (mostly through the kidneys, urine, or bile).

Pharmacodynamics

• Mechanism of Action – How a drug interacts with receptors, enzymes, or cells to produce its effect.
• Dose-Response Relationship – The relationship between drug dose and its therapeutic effect.
• Side Effects & Adverse Reactions – Undesirable effects that a drug may cause.

Drug Classification

Drugs are categorized based on their action, chemical structure, and therapeutic use. Some major classes include:

• Analgesics (Pain relievers, e.g., Paracetamol, Ibuprofen)
• Antibiotics (Fight infections, e.g., Penicillin, Amoxicillin)
• Antihypertensives (Lower blood pressure, e.g., Amlodipine, Enalapril)
• Diuretics (Increase urine output, e.g., Furosemide, Hydrochlorothiazide)

Routes of Drug Administration

• Oral (PO) – By mouth, e.g., tablets, capsules.
• Intravenous (IV) – Directly into veins, rapid action.
• Intramuscular (IM) – Injected into muscles.
• Subcutaneous (SC) – Under the skin.
• Topical – Applied to skin, e.g., creams, ointments.

Factors Affecting Drug Action

• Age, weight, genetics, disease conditions, and drug interactions.

Conclusion

General pharmacology provides the foundation for understanding drug actions, proper usage, and their effects on the body. Knowledge of pharmacology is essential for safe and effective medication use in healthcare.

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Autonomic Nervous System (ANS) in Pharmacology

The Autonomic Nervous System (ANS) is a part of the peripheral nervous system that controls involuntary body functions such as heart rate, digestion, and respiratory rate. It is divided into two major divisions:

Divisions of the ANS

Sympathetic Nervous System (SNS) – “Fight or Flight”

• Activated during stress, fear, or emergency situations.
• Increases heart rate, blood pressure, and respiratory rate.
• Dilates pupils and bronchioles.
• Reduces digestion and urinary functions.
• Major neurotransmitter: Norepinephrine (NE).
• Key receptors: Alpha (α) & Beta (β) adrenergic receptors.

Parasympathetic Nervous System (PNS) – “Rest and Digest”

• Active during rest and relaxation.
• Decreases heart rate and blood pressure.
• Enhances digestion, salivation, and urinary function.
• Constricts pupils and bronchioles.
• Major neurotransmitter: Acetylcholine (ACh).
• Key receptors: Muscarinic & Nicotinic receptors.

Pharmacology of ANS Drugs

ANS drugs are classified based on their action on the Sympathetic or Parasympathetic system:

Drugs Affecting the SNS (Adrenergic Drugs)

1. Adrenergic Agonists (Sympathomimetics) – Stimulate the SNS.
   • Example: Epinephrine (used in anaphylaxis), Salbutamol (asthma).
2. Adrenergic Antagonists (Sympatholytics) – Block SNS effects.
   • Example: Propranolol (for hypertension), Prazosin (for high BP).

Drugs Affecting the PNS (Cholinergic Drugs)

1. Cholinergic Agonists (Parasympathomimetics) – Stimulate the PNS.
   • Example: Pilocarpine (for glaucoma), Bethanechol (for urinary retention).
2. Cholinergic Antagonists (Parasympatholytics/Anticholinergics) – Block PNS effects.
   • Example: Atropine (used in bradycardia), Ipratropium (for COPD).

Clinical Uses of ANS Drugs

• Hypertension – Beta-blockers (e.g., Metoprolol) reduce heart rate.
• Asthma & COPD – Beta-2 agonists (e.g., Salbutamol) dilate airways.
• Glaucoma – Cholinergic drugs (e.g., Pilocarpine) reduce eye pressure.
• Bradycardia – Atropine increases heart rate.

Conclusion

The Autonomic Nervous System plays a crucial role in regulating involuntary body functions. Understanding its pharmacology helps in the effective use of drugs for conditions like hypertension, asthma, and heart diseases.

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Cardiovascular System in Pharmacology

The Cardiovascular System (CVS) consists of the heart and blood vessels, responsible for circulating blood, oxygen, and nutrients throughout the body. In pharmacology, drugs affecting the cardiovascular system are used to treat conditions like hypertension, heart failure, arrhythmias, and angina.

Major Components of the CVS

• Heart – Pumps blood throughout the body.
• Blood Vessels – Arteries, veins, and capillaries transport blood.
• Blood Pressure Regulation – Controlled by the heart rate, vascular resistance, and blood volume.

Pharmacology of Cardiovascular Drugs

Cardiovascular drugs are classified based on their action:

A. Antihypertensive Drugs (Lower Blood Pressure)

1. Beta-Blockers (e.g., Metoprolol, Propranolol) – Reduce heart rate and workload.
2. Calcium Channel Blockers (e.g., Amlodipine, Verapamil) – Relax blood vessels, lowering blood pressure.
3. ACE Inhibitors (e.g., Enalapril, Lisinopril) – Block angiotensin, reducing blood vessel constriction.
4. Diuretics (e.g., Furosemide, Hydrochlorothiazide) – Increase urine output, reducing blood volume.

B. Antianginal Drugs (Treat Chest Pain/Angina)

1. Nitrates (e.g., Nitroglycerin) – Dilate blood vessels to improve blood flow.
2. Beta-Blockers – Reduce heart oxygen demand.
3. Calcium Channel Blockers – Improve blood supply to the heart.

C. Heart Failure Drugs

1. Cardiac Glycosides (e.g., Digoxin) – Strengthen heart contractions.
2. Diuretics – Reduce fluid overload in heart failure patients.
3. ACE Inhibitors & Beta-Blockers – Improve heart function and reduce strain.

D. Antiarrhythmic Drugs (Treat Irregular Heartbeat)

1. Class I (Sodium Channel Blockers) – (e.g., Lidocaine, Quinidine) – Stabilize heart rhythm.
2. Class II (Beta-Blockers) – (e.g., Propranolol) – Control heart rate.
3. Class III (Potassium Channel Blockers) – (e.g., Amiodarone) – Prolong heart muscle recovery time.
4. Class IV (Calcium Channel Blockers) – (e.g., Verapamil) – Slow heart rate.

E. Anticoagulants & Antiplatelet Drugs (Prevent Blood Clots)

1. Anticoagulants (e.g., Heparin, Warfarin) – Prevent clot formation in conditions like deep vein thrombosis (DVT).
2. Antiplatelets (e.g., Aspirin, Clopidogrel) – Prevent platelets from clumping together, reducing heart attack risk.
3. Thrombolytics (e.g., Alteplase) – Break down existing clots in emergencies like stroke.

Clinical Uses of Cardiovascular Drugs

• Hypertension – ACE inhibitors, beta-blockers, and diuretics lower blood pressure.
• Heart Failure – Diuretics and digoxin improve heart function.
• Arrhythmias – Antiarrhythmic drugs regulate heart rhythm.
• Coronary Artery Disease (Angina & Heart Attack Prevention) – Nitrates and antiplatelets reduce heart stress.
• Stroke Prevention – Anticoagulants prevent clot formation.

Conclusion

Pharmacological management of the cardiovascular system is crucial in treating heart diseases, high blood pressure, and clot-related disorders. Proper use of these drugs improves heart function and overall health.

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Glucocorticoids & Thyroxine in Pharmacology

1. Glucocorticoids

Uses:

• Anti-inflammatory (e.g., asthma, arthritis, allergies).
• Immunosuppressive (e.g., autoimmune diseases, organ transplant).
• Management of adrenal insufficiency (e.g., Addison’s disease).

Side Effects:

• Long-term use can cause osteoporosis, muscle weakness, hyperglycemia, hypertension, weight gain, and immune suppression.
• Prolonged steroid use can lead to Cushing’s syndrome (moon face, abdominal obesity).

Interaction with Physical Therapy:

• Muscle atrophy and weakness require strength training.
• Osteoporosis increases fracture risk, so weight-bearing exercises are beneficial.
• Increased risk of infections due to immunosuppression, requiring precautions.

2. Thyroxine (T4 – Thyroid Hormone Replacement Therapy)

Uses:

• Treats hypothyroidism (e.g., Hashimoto’s thyroiditis).
• Supports metabolism, energy levels, and normal body function.

Side Effects:

• Overdose can cause hyperthyroidism symptoms like increased heart rate, weight loss, anxiety, and osteoporosis.
• Under-dosing leads to fatigue, weight gain, depression, and cold intolerance.

Interaction with Physical Therapy:

• Hyperthyroidism can cause muscle wasting and cardiovascular strain, requiring moderate exercise.
• Hypothyroidism may cause fatigue and joint stiffness, benefiting from flexibility and endurance training.
• Bone health monitoring is essential, especially in osteoporosis-prone individuals.

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Central Nervous System (CNS) – Pharmacology Notes

Overview of CNS

• The Central Nervous System (CNS) consists of the brain and spinal cord, controlling voluntary and involuntary body functions.
• CNS drugs act on neurotransmitters like dopamine, serotonin, GABA, glutamate, and acetylcholine to influence mood, cognition, and motor function.

Major Classes of CNS Drugs

A. CNS Stimulants (Increase Brain Activity)

• Used for: ADHD, narcolepsy, depression.
• Examples: Caffeine, Amphetamines (Adderall), Methylphenidate (Ritalin).
• Side Effects: Insomnia, increased heart rate, anxiety, addiction risk.

B. CNS Depressants (Reduce Brain Activity)

1. Sedatives & Hypnotics – Used for anxiety, insomnia.
   • Examples: Benzodiazepines (Diazepam), Barbiturates.
   • Side Effects: Drowsiness, dependence, respiratory depression.
2. General Anesthetics – Induce unconsciousness for surgery.
   • Examples: Propofol, Ketamine.
   • Side Effects: Low blood pressure, respiratory depression.

C. Antiepileptic Drugs (AEDs) (Prevent Seizures)

• Examples: Phenytoin, Carbamazepine, Valproic acid.
• Side Effects: Dizziness, sedation, liver toxicity.

D. Antidepressants (Treat Depression & Anxiety)

• Examples: SSRIs (Fluoxetine), Tricyclics (Amitriptyline).
• Side Effects: Weight gain, sexual dysfunction, nausea.

E. Antipsychotics (Treat Schizophrenia & Psychosis)

• Examples: Haloperidol, Clozapine, Risperidone.
• Side Effects: Movement disorders, sedation, weight gain.

F. Neurodegenerative Disease Drugs (For Alzheimer’s & Parkinson’s)

• Alzheimer’s: Donepezil, Rivastigmine (boost memory).
• Parkinson’s: Levodopa-Carbidopa (restore dopamine).
• Side Effects: Nausea, dizziness, involuntary movements.

CNS Drugs & Physical Therapy

• Sedatives & Antidepressants: May cause dizziness → fall precautions.
• Antiepileptics: Balance training required.
• Parkinson’s Drugs: Exercise improves mobility & coordination.

Conclusion

CNS drugs play a crucial role in treating mental, neurological, and movement disorders. Understanding their effects helps in optimizing therapy and patient care.

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Respiratory System – Therapeutic Agents

The respiratory system includes the lungs and airways, responsible for oxygen exchange. Several therapeutic agents are used to treat respiratory disorders like asthma, COPD, infections, and allergies.

Major Classes of Respiratory Drugs

A. Bronchodilators (Expand Airways)

1. Beta-2 Adrenergic Agonists – Relax airway muscles.

   • Examples: Salbutamol (short-acting), Salmeterol (long-acting).
   • Uses: Asthma, COPD.
   • Side Effects: Tremors, palpitations, headache.

2. Anticholinergics – Block bronchoconstriction.

   • Examples: Ipratropium, Tiotropium.
   • Uses: COPD, chronic bronchitis.
   • Side Effects: Dry mouth, blurred vision.

3. Methylxanthines – Relax airway muscles, improve breathing.

   • Examples: Theophylline, Aminophylline.
   • Uses: Asthma, COPD.
   • Side Effects: Nausea, insomnia, tachycardia.

B. Anti-Inflammatory Drugs (Reduce Inflammation)

1. Corticosteroids – Suppress inflammation.

   • Examples: Budesonide, Fluticasone (inhaled), Prednisone (oral).
   • Uses: Asthma, COPD.
   • Side Effects: Hoarseness, osteoporosis (long-term use).

2. Leukotriene Receptor Antagonists (LTRAs) – Prevent airway inflammation.

   • Examples: Montelukast, Zafirlukast.
   • Uses: Asthma, allergic rhinitis.
   • Side Effects: Headache, liver dysfunction.

C. Cough Suppressants & Expectorants

1. Antitussives (Cough Suppressants) – Reduce dry cough.

   • Examples: Codeine, Dextromethorphan.
   • Uses: Persistent cough.
   • Side Effects: Drowsiness, constipation (opioids).

2. Expectorants & Mucolytics – Loosen mucus for easier clearance.

   • Examples: Guaifenesin (expectorant), Acetylcysteine (mucolytic).
   • Uses: Productive cough, bronchitis.
   • Side Effects: Nausea, dizziness.

D. Antihistamines (Block Allergy Symptoms)

• Examples: Loratadine, Cetirizine, Diphenhydramine.
• Uses: Allergic rhinitis, asthma, cold symptoms.
• Side Effects: Drowsiness, dry mouth.

Interaction with Physical Therapy

• Bronchodilators: May cause increased heart rate; monitor during exercise.
• Corticosteroids: Risk of osteoporosis; weight-bearing exercises needed.
• Antihistamines: May cause drowsiness; adjust therapy sessions accordingly.

Conclusion

Respiratory drugs play a crucial role in managing airway diseases. Proper use of bronchodilators, anti-inflammatory agents, and cough treatments enhances breathing and overall lung function.

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Gastrointestinal System – Therapeutic Agents

The gastrointestinal (GI) system is responsible for digestion, absorption, and elimination. Common GI disorders include peptic ulcers and diarrhea, which require specific therapeutic agents for treatment.

Therapeutic Agents for Peptic Ulcers

Peptic ulcers are open sores in the stomach or duodenal lining caused by H. pylori infection, NSAIDs, or excessive acid production.

Drug Classes for Peptic Ulcer Treatment

1. Proton Pump Inhibitors (PPIs) – Reduce acid secretion.

   • Examples: Omeprazole, Pantoprazole.
   • Uses: Peptic ulcers, GERD.
   • Side Effects: Headache, nausea, increased fracture risk (long-term use).

2. H2-Receptor Blockers – Decrease stomach acid production.

   • Examples: Ranitidine (withdrawn in many countries), Famotidine.
   • Uses: Peptic ulcers, reflux disease.
   • Side Effects: Dizziness, diarrhea, fatigue.

3. Antacids – Neutralize stomach acid.

   • Examples: Magnesium hydroxide, Aluminum hydroxide.
   • Uses: Temporary ulcer symptom relief, acid reflux.
   • Side Effects: Diarrhea (magnesium-based), constipation (aluminum-based).

4. Mucosal Protectants – Form a protective layer over ulcers.

   • Examples: Sucralfate, Bismuth subsalicylate.
   • Uses: Peptic ulcers, ulcer prevention.
   • Side Effects: Constipation, black stools (bismuth).

5. Antibiotics (For H. pylori Infection) – Eradicate bacteria causing ulcers.

   • Examples: Amoxicillin, Clarithromycin, Metronidazole.
   • Uses: H. pylori-related peptic ulcers.
   • Side Effects: Nausea, diarrhea, antibiotic resistance risk.

Therapeutic Agents for Diarrhea

Diarrhea is the frequent passage of loose stools, often due to infections, IBS, or medication side effects.

Drug Classes for Diarrhea Treatment

1. Antimotility Agents – Slow bowel movement.

   • Examples: Loperamide (Imodium), Diphenoxylate.
   • Uses: Acute & chronic diarrhea, IBS.
   • Side Effects: Drowsiness, constipation, bloating.

2. Adsorbents – Absorb toxins and fluid in the intestine.

   • Examples: Activated charcoal, Kaolin-pectin.
   • Uses: Mild diarrhea, toxin-induced diarrhea.
   • Side Effects: Constipation, bloating.

3. Probiotics – Restore gut bacteria balance.

   • Examples: Lactobacillus, Saccharomyces boulardii.
   • Uses: Antibiotic-associated diarrhea, IBS.
   • Side Effects: Gas, bloating (rare).

4. Oral Rehydration Solutions (ORS) – Replace lost fluids and electrolytes.

   • Examples: WHO ORS, electrolyte powders.
   • Uses: Prevent dehydration in severe diarrhea.
   • Side Effects: None (if taken correctly).

Interaction with Physical Therapy

Peptic Ulcer Drugs & Physical Therapy

• PPIs & H2 blockers: Long-term use may cause osteoporosis → Weight-bearing exercises help maintain bone health.
• Antacids: May cause electrolyte imbalances → Monitor hydration and muscle function.
• Antibiotics (for H. pylori): Can cause GI upset → Exercise should be adjusted if symptoms worsen.

Diarrhea Drugs & Physical Therapy

• Antimotility agents (Loperamide): Can cause drowsiness → Caution with balance and coordination exercises.
• ORS therapy: Essential for dehydration → Monitor hydration levels during exercise.
• Probiotics: May improve gut health, leading to better energy levels for physical activity.

Conclusion

Therapeutic agents for peptic ulcers focus on acid suppression and mucosal protection, while diarrhea treatments aim at controlling stool frequency and replenishing fluids. Understanding these medications’ effects helps in safe and effective physical therapy management.

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Diabetes Mellitus – Drug Therapy

Diabetes Mellitus (DM) is a chronic metabolic disorder characterized by high blood sugar levels due to insufficient insulin production or resistance to insulin. It is classified into:

• Type 1 Diabetes (T1DM): Autoimmune destruction of pancreatic beta cells → Insulin deficiency.
• Type 2 Diabetes (T2DM): Insulin resistance + impaired insulin secretion.
• Gestational Diabetes: Occurs during pregnancy, usually resolves postpartum.

Drug Therapy for Diabetes Mellitus

A. Insulin Therapy (Used in T1DM & T2DM)

• Types of Insulin:
  • Rapid-Acting: Lispro, Aspart (Onset: 15 min, Peak: 1-2 hrs).
  • Short-Acting: Regular Insulin (Onset: 30 min, Peak: 2-4 hrs).
  • Intermediate-Acting: NPH Insulin (Onset: 1-2 hrs, Peak: 4-8 hrs).
  • Long-Acting: Glargine, Detemir (No peak, lasts 24 hrs).
• Side Effects: Hypoglycemia, weight gain, lipodystrophy.

B. Oral Hypoglycemic Agents (Used in T2DM)

1. Biguanides (Insulin Sensitizers)

   • Example: Metformin.
   • Mechanism: Reduces glucose production in the liver, increases insulin sensitivity.
   • Side Effects: GI upset, lactic acidosis (rare).

2. Sulfonylureas (Insulin Secretagogues)

   • Examples: Glibenclamide, Glipizide.
   • Mechanism: Stimulate pancreatic beta cells to release insulin.
   • Side Effects: Hypoglycemia, weight gain.

3. Meglitinides (Short-Acting Insulin Secretagogues)

   • Examples: Repaglinide, Nateglinide.
   • Mechanism: Similar to sulfonylureas but with a shorter action.
   • Side Effects: Hypoglycemia, weight gain.

4. Thiazolidinediones (TZDs) (Insulin Sensitizers)

   • Examples: Pioglitazone, Rosiglitazone.
   • Mechanism: Improve insulin sensitivity in muscles and fat cells.
   • Side Effects: Fluid retention, weight gain, risk of heart failure.

5. DPP-4 Inhibitors (Incretin Enhancers)

   • Examples: Sitagliptin, Vildagliptin.
   • Mechanism: Increase insulin secretion, decrease glucagon release.
   • Side Effects: Pancreatitis, joint pain.

6. SGLT2 Inhibitors (Glucose Excretion Enhancers)

   • Examples: Canagliflozin, Empagliflozin.
   • Mechanism: Increase glucose excretion via urine.
   • Side Effects: Urinary tract infections, dehydration.

7. GLP-1 Receptor Agonists (Incretin Mimetics)

   • Examples: Liraglutide, Exenatide.
   • Mechanism: Slow gastric emptying, promote insulin secretion.
   • Side Effects: Nausea, weight loss, pancreatitis.

Interaction with Physical Therapy

A. Hypoglycemia Risk (Low Blood Sugar, <70 mg/dL)

• Common with insulin, sulfonylureas, and meglitinides.
• Symptoms: Dizziness, confusion, sweating, weakness, tremors.
• PT Consideration: Ensure patient eats before exercise; keep glucose sources handy.

B. Exercise-Induced Hyperglycemia (High Blood Sugar, >250 mg/dL)

• Seen in poorly controlled diabetes due to stress hormone release.
• PT Consideration: Avoid intense exercise if blood sugar is very high; encourage hydration.

C. Neuropathy & Foot Care

• Diabetic neuropathy leads to reduced sensation, foot ulcers, risk of injury.
• PT Consideration: Use proper footwear, monitor for wounds, avoid high-impact activities.

D. Cardiovascular Risks

• Diabetes increases the risk of hypertension, heart disease.
• PT Consideration: Monitor heart rate and blood pressure during exercise.

E. Dehydration Risk

• SGLT2 inhibitors increase urine output, leading to dehydration.
• PT Consideration: Encourage hydration, avoid excessive sweating.

Conclusion

Diabetes treatment includes insulin for Type 1 DM and oral hypoglycemics for Type 2 DM. These drugs have significant interactions with physical activity, requiring careful monitoring of blood sugar, hydration, and foot care. Safe, moderate exercise improves insulin sensitivity and overall glucose control.

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Geriatric Pharmacological Challenges

Introduction

Aging affects drug metabolism, distribution, and elimination, leading to altered drug responses and increased risks of adverse effects in the elderly population. Polypharmacy (use of multiple medications), decreased organ function, and drug interactions make pharmacological management in geriatrics complex. These changes significantly impact physical therapy (PT), requiring careful intervention strategies.

Geriatric Pharmacological Challenges

A. Altered Pharmacokinetics in the Elderly

1. Absorption: Minimal changes with aging, but delayed gastric emptying may affect some drugs.
2. Distribution:
   • Increased fat content → Prolonged action of lipid-soluble drugs (e.g., benzodiazepines).
   • Decreased muscle mass & water content → Higher plasma concentration of water-soluble drugs (e.g., digoxin).
3. Metabolism:
   • Reduced liver enzyme activity → Slower drug metabolism (e.g., prolonged effects of warfarin).
4. Excretion:
   • Declined kidney function → Drug accumulation, leading to toxicity (e.g., aminoglycosides, NSAIDs).

B. Polypharmacy & Drug Interactions

• Increased risk of adverse drug reactions (ADRs) and drug interactions.
• Commonly used drugs with high interaction risks:
  • Antihypertensives (beta-blockers, diuretics) → Risk of hypotension, falls.
  • Sedatives & Hypnotics (benzodiazepines) → Drowsiness, fall risk.
  • Opioids & NSAIDs → Risk of GI bleeding, kidney impairment.

3. Common Drug Classes & Their Effects on Physical Therapy

4. Effects on Physical Therapy & Considerations

1. Fall Risk & Balance Issues

   • Caused by sedatives, antihypertensives, and muscle relaxants.
   • PT Consideration: Focus on fall prevention, balance training, strength exercises.

2. Muscle Weakness & Fatigue

   • Due to steroids, beta-blockers, statins.
   • PT Consideration: Low-intensity strength & endurance training, gradual progression.

3. Joint & Bone Health

   • Osteoporosis risk from corticosteroids.
   • PT Consideration: Weight-bearing exercises, resistance training, fall precautions.

4. Cardiovascular Risks

   • Beta-blockers reduce exercise tolerance.
   • PT Consideration: Monitor heart rate, blood pressure during therapy.

5. Cognitive & Psychomotor Impairments

   • Antidepressants & sedatives can impair cognition.
   • PT Consideration: Simplify instructions, increase supervision.

5. Conclusion

Elderly patients require individualized pharmacological & physical therapy approaches to minimize drug-related impairments. Understanding drug interactions, side effects, and exercise modifications can enhance therapy outcomes, reduce fall risk, and improve overall function in geriatrics.

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Routes and Modes of Drug Administration (Brief Overview)

The route of drug administration refers to how a drug is introduced into the body. The choice depends on factors like drug properties, onset of action, patient condition, and convenience.

1. Major Routes of Drug Administration

A. Enteral Route (Via Gastrointestinal Tract)

• Oral (PO) – Most common, convenient, and economical.

  • Examples: Tablets, capsules, syrups (e.g., Paracetamol, Metformin).
  • Pros: Safe, easy, suitable for long-term use.
  • Cons: Slow onset, affected by food and digestive enzymes.

• Sublingual (SL) & Buccal – Placed under the tongue or in the cheek for direct absorption into the bloodstream.

  • Examples: Nitroglycerin (for angina).
  • Pros: Rapid action, bypasses the liver (no first-pass metabolism).
  • Cons: Limited drugs suitable, may cause irritation.

• Rectal (PR) – Used when oral intake is not possible (unconscious patients, vomiting).

  • Examples: Suppositories (e.g., Diazepam for seizures).
  • Pros: Bypasses liver partially, useful for infants and elderly.
  • Cons: Uncomfortable, irregular absorption.

B. Parenteral Route (Direct Entry into Systemic Circulation)

• Intravenous (IV) – Directly into the bloodstream.

  • Examples: Antibiotics, Chemotherapy drugs.
  • Pros: Fastest action, 100% bioavailability.
  • Cons: Risk of infections, expensive, requires trained personnel.

• Intramuscular (IM) – Injected into muscle for gradual absorption.

  • Examples: Vaccines, Painkillers (e.g., Diclofenac).
  • Pros: Faster than oral, long-lasting effects.
  • Cons: Painful, risk of muscle damage.

• Subcutaneous (SC) – Injected under the skin for slow, sustained release.

  • Examples: Insulin, Heparin.
  • Pros: Easy, steady absorption.
  • Cons: Limited volume of drug can be administered.

• Intradermal (ID) – Injected into the skin, mainly for diagnostic purposes.

  • Examples: Tuberculin skin test, Allergy tests.
  • Pros: Localized effect.
  • Cons: Requires expertise.

C. Other Routes of Administration

• Inhalation – Rapid absorption via lungs.

  • Examples: Asthma inhalers (Salbutamol).
  • Pros: Fast action, minimal systemic effects.
  • Cons: Requires proper technique.

• Topical (Skin/Local Application) – Direct application to skin or mucous membranes.

  • Examples: Creams, Ointments (Hydrocortisone for inflammation).
  • Pros: Localized effect, fewer systemic side effects.
  • Cons: Limited penetration, frequent application needed.

• Transdermal (Patches) – Absorbed through the skin into systemic circulation.

  • Examples: Nicotine patches, Fentanyl patches.
  • Pros: Sustained drug release, avoids first-pass metabolism.
  • Cons: Slow onset, skin irritation possible.

• Intrathecal (Spinal Injection) – Directly into cerebrospinal fluid (CSF).

  • Examples: Epidural anesthesia, Chemotherapy.
  • Pros: Direct CNS action.
  • Cons: Highly invasive, risk of infection.

2. Choosing the Right Route

• Rapid effect needed? → IV, Sublingual, Inhalation
• Long-term therapy? → Oral, Transdermal, IM (depot injections)
• Localized treatment? → Topical, Intrathecal
• Unconscious patient? → IV, PR, IM

Conclusion

Different routes of drug administration impact drug absorption, effectiveness, and patient compliance. The choice depends on the urgency, drug properties, and patient condition for optimal therapeutic outcomes.

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