DrX %20(1).png)
DrX Whiz Niraj
Introduction to Pharmacology & Pharmacokinetics
Complete B.Pharm Notes | Essential Core Concepts
1. Definition & History
What is Pharmacology?
Pharmacology is the branch of medical and pharmaceutical science that deals with the study of drugs, their sources, properties, uses, mechanisms of action, adverse effects, absorption, distribution, metabolism, and excretion.
Pharmakon = Drug | Logos = Study
Pharmacology helps healthcare professionals to precisely understand how drugs act in the body, how the body reacts to drugs, how to safely prescribe medicines, and how to prevent dangerous adverse drug reactions.
Historical Landmarks
- Ancient Period: Humans relied on plants, herbs, minerals, and animal products as primitive medicines. Ayurveda (India) and Chinese medicine are among the oldest documented medical systems.
- Hippocrates (460–370 BC): Known as the Father of Medicine, he emphasized scientific observation in the medical field.
- Galen (130–200 AD): Prepared and documented medicines from natural sources. Such crude plant preparations are still called Galenicals today.
- Paracelsus (1493–1541): Revolutionized toxicology by stating, "All substances are poisons; only the dose determines the poison."
- Friedrich Sertürner (1805): Isolated the first active pharmaceutical ingredient, Morphine, from opium.
- Rudolf Buchheim: Established the world's very first pharmacology laboratory.
- Oswald Schmiedeberg: Officially recognized as the founder of modern scientific pharmacology.
2. Scope & Sources of Drugs
Scope of Pharmacology
Pharmacodynamics
Study of the biological and physiological effects of drugs on the body. (What the drug does to the body).
Pharmacokinetics
Study of the movement of drugs in the body, specifically ADME. (What the body does to the drug).
Toxicology & Chemotherapy
Toxicology: The study of poisonous effects of drugs. Chemotherapy: Use of specific chemicals to kill systemic infections or cancer cells.
Pharmacovigilance & Genetics
Pharmacovigilance: Monitoring and preventing adverse drug reactions. Pharmacogenetics: Study of genetic influence on drug response.
Sources of Drugs
Drugs may prevent, diagnose, cure, or relieve symptoms. They are extracted or synthesized from various sources:
| Source Type | Description & Famous Examples |
|---|---|
| 🌿 Plant Sources | Leaves, roots, barks, or stems. E.g., Morphine (Opium poppy), Atropine (Belladonna), Digoxin (Digitalis). |
| 🐄 Animal Sources | Extracted from animal organs/fluids. E.g., Insulin (pig/cow pancreas), Thyroxine, Heparin (porcine intestine). |
| 🪨 Mineral Sources | Naturally occurring inorganic materials. E.g., Iron, Magnesium sulfate, Sodium bicarbonate. |
| 🧫 Microbial Sources | Extracted from fungi and bacteria. E.g., Penicillin (Penicillium notatum), Streptomycin. |
| 🧪 Synthetic Sources | Prepared purely in chemical labs. E.g., Paracetamol, Sulfonamides. (Semi-synthetic includes Amoxicillin). |
| 🧬 Biotechnology | Produced by modern genetic engineering (rDNA tech). E.g., Recombinant human insulin, Monoclonal antibodies. |
3. Routes of Drug Administration
Drug administration means the specific path by which a drug is brought into contact with the body. Choosing the right route is vital for therapeutic success.
Concept of "Essential Drugs"
Introduced by the World Health Organization (WHO), essential drugs are those medicines that satisfy the basic healthcare needs of the majority of the population. They must be continuously available, completely safe, effective, and highly affordable.
| Route Category | Sub-Types & Examples | Key Advantages / Disadvantages |
|---|---|---|
| 1. Enteral Route (Via GI Tract) |
|
Oral: Safe & economical, but slow action and suffers from first-pass metabolism. Sublingual: Rapid absorption, bypasses the liver completely. |
| 2. Parenteral Route (Injections/Bypass GI) |
|
IV: Immediate emergency action, 100% bioavailability. Risk: Pain, infection, requires skilled staff. |
| 3. Topical Route (Local Surface) |
Skin, eyes, ears, mucous membranes (Ointments, Creams, Drops). | High local concentration without causing systemic side effects. |
| 4. Inhalation Route (Lungs) |
Inhalers, Nebulizers (e.g., Salbutamol for Asthma), General anesthetics. | Extremely rapid action due to the massive surface area of the lungs. |
4. Pharmacodynamics (Receptors & Drugs)
Receptors are specialized macromolecular protein structures present on cell surfaces or inside cells that recognize and interact specifically with a drug to produce a cellular response.
✅ Agonists
An agonist is a drug that possesses both Affinity (ability to bind) and Intrinsic Activity (ability to activate). It binds to receptors and mimics the natural body chemicals. (e.g., Adrenaline, Morphine).
- Full Agonist: Produces 100% maximum response.
- Partial Agonist: Produces a sub-maximal response, even when all receptors are occupied.
❌ Antagonists
Antagonists have Affinity but ZERO Intrinsic Activity. They bind to receptors but do not produce any internal response, effectively blocking the natural agonists. (e.g., Naloxone, Atenolol).
Types of Antagonists
- Competitive Antagonist: Competes for the same receptor site as the agonist. It is reversible, meaning its block can be overcome if we flood the area by increasing the agonist dose (e.g., Atropine blocking Acetylcholine).
- Non-Competitive Antagonist: Binds irreversibly or at a totally different allosteric site on the receptor. Its block cannot be overcome even if we give massive doses of the agonist (e.g., Phenoxybenzamine).
Important Pharmacological Terms
- Spare Receptors: Extra receptors present beyond what is required for a maximum response. They increase the overall sensitivity of the tissue to a drug.
- Tolerance: The requirement of higher doses of a drug to produce a given effect, which was originally achieved by lower doses (e.g., Morphine, Alcohol).
- Tachyphylaxis: Acute, rapid development of tolerance after repeated administration in a very short time interval (e.g., Ephedrine).
- Idiosyncrasy: An abnormal, unpredictable response to a drug specific to an individual, usually due to genetic variations.
- Drug Allergy: An immune-mediated hypersensitivity reaction (e.g., Penicillin causing skin rash or anaphylaxis).
- Dependence & Addiction: Physical (withdrawal symptoms) or psychological (emotional craving) reliance on a drug.
5. Pharmacokinetics (ADME)
Pharmacokinetics simply means the study of what the body does to the drug. It comprises four phases: A.D.M.E.
1. Absorption & Membrane Transport
Movement of the active drug from the site of administration into the systemic bloodstream. Drugs cross biological membranes using:
- Passive Diffusion: Movement from high to low concentration. Needs lipid solubility. No ATP energy required.
- Facilitated Diffusion: Uses specialized carrier proteins but still requires no energy.
- Active Transport: Movement against a concentration gradient. Requires ATP energy (e.g., Levodopa transport).
2. Distribution
Once in the blood, the drug spreads out into tissues, organs, and intracellular fluids. This heavily depends on:
- Plasma Protein Binding: Many drugs strongly bind to plasma albumin. Note: Only the "free" unbound drug is pharmacologically active!
- Blood Brain Barrier (BBB): A tight barrier that protects the brain. Only highly lipid-soluble drugs can cross the BBB.
3. Metabolism (Biotransformation)
The chemical alteration of the drug in the body. The Liver is the primary organ for metabolism. Its main goal is to convert highly active, lipid-soluble drugs into inactive, highly water-soluble metabolites so they can be peed out easily.
Phase I Reactions
Non-synthetic reactions like Oxidation, Reduction, and Hydrolysis. Primarily utilizes the Cytochrome P450 (CYP450) enzyme system.
Phase II Reactions
Synthetic/Conjugation reactions like Glucuronidation, Sulfation, and Acetylation. Makes the drug highly polar and ready for excretion.
Enzyme Induction vs Inhibition
Induction: Some drugs increase liver enzyme synthesis. This increases the metabolism of co-administered drugs, leading to therapeutic failure. (Inducers: Rifampicin, Phenobarbital).
Inhibition: Some drugs block liver enzymes. This stops metabolism, leading to drug accumulation and dangerous toxicity. (Inhibitors: Erythromycin, Cimetidine).
4. Excretion
The final removal of the intact drug or its metabolites from the body. Main routes include: Kidneys (Urine), Bile (Feces), Lungs (Exhaled air), Sweat, and Breast Milk. Renal excretion depends heavily on Glomerular filtration and Tubular secretion.
6. Kinetics of Elimination & Half-Life
First Order Kinetics
Rate of elimination is directly proportional to plasma drug concentration. A constant fraction (e.g., 50%) is eliminated per unit time. Maximum drugs follow this.
Zero Order Kinetics
Rate of elimination is independent of concentration. A constant amount (e.g., 10mg) is eliminated per unit time. (e.g., Alcohol, high dose Phenytoin).
Key Pharmacokinetic Formulas
Time strictly required for the plasma concentration of a drug to safely reduce by exactly 50%. It dictates the dosing interval.
VVI Exam Questions (University Format)
Make sure to study these frequently asked questions thoroughly before your final examinations:
- Very Short Answer (2 Marks):
- Define Bioavailability and Half-life (t1/2).
- What are Galenicals? Give examples.
- Differentiate between Tachyphylaxis and Tolerance.
- Short Answer (5 Marks):
- Discuss various transport mechanisms across biological membranes.
- Explain Enzyme Induction and Inhibition with two examples each.
- Discuss Phase 1 and Phase 2 metabolic biotransformation reactions.
- Long Answer (10 Marks):
- Define Pharmacokinetics. Elaborate on the factors affecting the Absorption and Distribution of drugs.
- Classify the various Routes of Drug Administration detailing their relative advantages, disadvantages, and specific indications.
- What is Receptor Antagonism? Explain Competitive and Non-competitive antagonism in detail with relevant examples and graphs.