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DrX Whiz Niraj
Welcome to DrX Whiz Niraj. In this post, we will cover the complete notes for B.Pharm 4th Semester, Pharmacology I (Unit 2). This unit covers Pharmacodynamics, Drug Interactions, Adverse Drug Reactions (ADR), and Clinical Trials.
Pharmacodynamics
Principles of Drug Action
Drugs act mainly by the following mechanisms:
- Stimulation: Increases activity of cells or organs (e.g., Adrenaline stimulates the heart).
- Depression: Reduces activity of organs (e.g., General anesthetics depress CNS).
- Irritation: Irritates tissues (e.g., Purgatives irritate the intestine).
- Replacement: Replaces deficient substances (e.g., Insulin in diabetes, Iron in anemia).
- Cytotoxic Action: Destroys microorganisms or cancer cells (e.g., Antibiotics, Anticancer drugs).
Receptor Theory
Classification of Receptors
1. G-Protein Coupled Receptors (GPCR)
Largest family of receptors. Drug binds \(\rightarrow\) Activates G-protein \(\rightarrow\) Produces second messengers (cAMP, IP3, DAG, Ca++).
Ex: Adrenergic & Dopamine receptors.
2. Ion Channel Receptors
Regulate ion flow across the membrane. Rapid response (milliseconds).
Ex: Nicotinic receptor, GABA receptor.
3. Enzyme Linked Receptors
Possess transmembrane enzyme activity. Drug binding activates intracellular enzymes like tyrosine kinase.
Ex: Insulin receptor.
4. Intracellular Receptors
Regulate transcription factors inside the nucleus. Slow onset but long duration.
Ex: Steroid & Thyroid hormone receptors.
Receptor Regulation
- Up-Regulation: Increase in receptor number (occurs after prolonged antagonist use).
- Down-Regulation: Decrease in receptor number (occurs after prolonged agonist exposure, e.g., Insulin).
Dose Response Relationship
It is the relationship between the drug dose and the response produced.
- Potency: Amount of drug required to produce an effect. A more potent drug requires a smaller dose.
- Efficacy: Maximum response produced by a drug.
Therapeutic Index (TI)
It indicates the safety margin of a drug. Higher TI = Safer Drug.
(Where TD50 = Toxic dose in 50%, ED50 = Effective dose in 50%)
Adverse Drug Reactions (ADR)
Types of ADR
Type A (Augmented)
Dose dependent & predictable.
Ex: Hypoglycemia by insulin.
Type B (Bizarre)
Unpredictable & not dose-dependent.
Ex: Penicillin allergy.
Type C (Chronic)
Occurs after long-term therapy.
Ex: Steroid-induced osteoporosis.
Type D (Delayed)
Appears after a long time.
Ex: Carcinogenesis, Teratogenicity.
Clinical Evaluation & Trials
Phase I Trial
Subjects: 20-100 Healthy volunteers.
Purpose: Safety, Dose determination, Pharmacokinetics.
Phase II Trial
Subjects: 100-300 Patients with disease.
Purpose: Determine Efficacy and short-term side effects.
Phase III Trial
Subjects: 1000-3000 Large patient group.
Purpose: Confirm efficacy, compare with standard treatments.
Phase IV Trial
Post-Marketing:
Purpose: Detect rare ADRs and monitor long-term safety among the general public.
2 Marks Questions (Short Answers)
- Define Pharmacodynamics.
- What is the difference between Potency and Efficacy?
- Define Therapeutic Index (TI) with its formula.
- What is Pharmacovigilance?
- Differentiate between Synergism and Antagonism.
- What is Type A and Type B Adverse Drug Reaction?
5 Marks Questions (Short Essays)
- Explain the different phases of Clinical Trials in detail.
- Write a short note on G-Protein Coupled Receptors (GPCR) and signal transduction.
- Discuss the various factors modifying drug action.
- Classify Adverse Drug Reactions (ADR) with suitable examples.
10 Marks Questions (Long Essays)
- Define Receptors. Classify them in detail and explain the mechanism of action of transmembrane and intracellular receptors.
- What are Drug Interactions? Explain Pharmacokinetic and Pharmacodynamic drug interactions in detail with examples.