Comprehensive General Pharmacology Notes Based on KD Tripathi

This presentation covers important concepts of General Pharmacology based on KD Tripathi, including routes of drug administration, agonists & antagonists, addiction, tolerance, dependence, tachyphylaxis, idiosyncrasy, and drug allergy. Designed for B.Pharm/M.Pharm students, it provides concise, point-wise explanations useful for classroom presentations, exams, and quick revision.

1. General Pharmacology RAJKISHOR SAHU M PHARM (PHARMACOLOGY) Chitkara university,punjab

2. Definition of Pharmacology Pharmacology is defined as the branch of medical science that deals with the study of drugs and their interaction with living organisms. The term pharmacology comes from two Greek words: Pharmakon = drug Logos = study or discourse Thus, pharmacology literally means “the study of drugs.” Drugs are chemical substances, whether natural, synthetic, or semi-synthetic, which can modify the functions of living systems when introduced in adequate amounts. Pharmacology has two broad aspects: Pharmacokinetics – what the body does to the drug (absorption, distribution, metabolism, excretion). Pharmacodynamics – what the drug does to the body (mechanism of action, effects on tissues/organs, therapeutic and toxic effects). Pharmacology bridges the gap between basic sciences (physiology, biochemistry, pathology) and clinical medicine, making it central to rational drug therapy.

3. 2. Historical Background of Pharmacology The history of pharmacology is closely related to the history of medicine. Drugs have been used by humans since ancient times, but the scientific study of drugs is relatively recent. A. Ancient Period In ancient civilizations, treatment of disease relied on natural substances : Plants : opium poppy (morphine), cinchona bark (quinine), digitalis leaves. Animal products : liver for vitamin A, honey for wound healing. Minerals : iron salts, sulphur . Ancient Indian system ( Ayurveda ), Chinese medicine, and Unani contributed many herbal formulations that are still used. B. Middle Ages Use of crude drugs and plant extracts continued. Alchemy and traditional medicine flourished, but scientific understanding was lacking. C. Beginning of Modern Pharmacology (19th Century) The 1800s marked the scientific era of pharmacology , when pure active principles were isolated: Morphine (1806) from opium. Quinine (1820) from cinchona bark. Atropine, digitalis glycosides.

4. 3. Scope of Pharmacology Pharmacology is a vast field encompassing basic science, experimental studies, and clinical applications. Its scope extends from drug discovery to therapeutic use in patients. A. Subdivisions of Pharmacology General Pharmacology Basic principles of drug action, pharmacokinetics, pharmacodynamics, drug interactions, and adverse effects. Systemic Pharmacology Study of actions of drugs on specific organ systems (e.g., cardiovascular drugs, CNS drugs, endocrine drugs). Clinical Pharmacology Application of pharmacology to humans in disease conditions. Includes therapeutic uses, rational prescribing, adverse drug reaction monitoring, and drug development. Pharmacotherapeutics Deals with the use of drugs in prevention, diagnosis, and treatment of diseases. Toxicology Study of harmful effects of drugs, poisons, and environmental chemicals. Chemotherapy Use of drugs to destroy/inhibit parasites, bacteria, viruses, fungi, or cancer cells without harming the host. Pharmacognosy Study of drugs obtained from natural sources (plants, animals, minerals). Pharmacovigilance Monitoring, detection, and prevention of adverse drug reactions and ensuring safe use of medicines.

5. . Nature and Sources of Drugs A. Nature of Drugs Drugs are chemical substances of natural or synthetic origin. They produce biological effects by interacting with targets such as receptors, enzymes, ion channels, nucleic acids, or cell membranes. Drugs can be therapeutic, diagnostic, or prophylactic. A drug is distinguished from a nutrient or normal body constituent by its intended use to modify or prevent a pathological condition. . Sources of Drugs Drugs are derived from a wide variety of sources. Plant Sources Many important drugs are obtained from plants. Examples: Morphine (opium poppy). Quinine (cinchona bark). Atropine (Atropa belladonna). Digitalis glycosides (Digitalis purpurea). Animal Sources Hormones, enzymes, and biological products. Examples: Insulin (pancreas of pigs/cattle, now recombinant). Heparin (porcine intestinal mucosa). Thyroid extract. Mineral Sources Simple inorganic substances used as drugs. Examples: Iron (ferrous sulfate). Magnesium sulfate. Lithium salts.

6. Routes of Drug Administration The route of administration of a drug refers to the path by which a drug is taken into the body . The choice of route depends on the drug’s properties, the desired speed of action, the condition of the patient, and convenience. A. Enteral Routes Oral (per os ) Most common, convenient, safe, and economical. Drugs are absorbed mainly from the small intestine. Limitations: slow onset, variable absorption, affected by food, gastric acid, and first-pass metabolism. Examples: paracetamol, antibiotics. Sublingual (under the tongue) Drug placed beneath tongue, absorbed directly into systemic circulation. Rapid action, avoids first-pass metabolism. Example: nitroglycerin for angina.

7. 3- Rectal Drug given as suppository or enema. Useful in unconscious or vomiting patients. Partially avoids first-pass metabolism. Example: diazepam suppository in seizures, paracetamol in children. B. Parenteral Routes (injection routes Intravenous (IV) Directly into bloodstream. 100% bioavailability, rapid action, useful in emergencies. Risk: infection, thrombophlebitis, overdose. Example: IV fluids, antibiotics, morphine. Intramuscular (IM) Drug injected into large muscle (deltoid, gluteus). Faster than oral, depot preparations possible. Example: vaccines, antipsychotics.

8. Subcutaneous (SC) Injected beneath skin. Slower, prolonged absorption. Example: insulin, heparin. Other specialized routes Intradermal (BCG test). Intrathecal (spinal anesthesia). Intra-arterial (chemotherapy ). C. Topical & Local Routes Skin : ointments, creams, patches (transdermal). Eye/Ear/Nose : drops, sprays. Inhalation : gases, vapors, aerosols (asthma inhalers). Vaginal/Urethral : suppositories, creams .

9. Agonist and Antagonist Drugs act by binding to specific receptors in the body. Agonist Drug that binds to receptor and activates it to produce a biological response. Has both affinity (ability to bind) and intrinsic activity (ability to activate). Example: adrenaline is a β-agonist (↑ heart rate). Antagonist Drug that binds to receptor but does not activate it ; instead, blocks the action of agonist. Has affinity but no intrinsic activity. Example: propranolol (β-blocker). Partial agonist : acts as agonist but produces submaximal response even at full receptor occupancy (e.g., buprenorphine). Inverse agonist : binds to receptor and produces opposite effect (e.g., antihistamines at H1 receptor).

10. Addiction Definition : A chronic, relapsing disorder characterized by compulsive drug-seeking behavior and loss of control despite harmful consequences. Drugs that cause addiction act on brain reward pathways (dopamine system). Features : Psychological craving. Tolerance and dependence develop. Social, occupational, and health deterioration. Examples : opioids (heroin, morphine), alcohol, cocaine, nicotine. Tolerance Definition : Decreased response to a drug after repeated administration, requiring larger doses to achieve the same effect. Mechanisms : Pharmacokinetic (↑ drug metabolism). Pharmacodynamic (↓ receptor sensitivity). Behavioral (patient learns to overcome drug effects). Clinical examples : Morphine: tolerance to analgesic and euphoric effects. Nitroglycerin : tolerance develops with continuous use. Significance : limits long-term therapeutic use.

11. Dependence Dependence refers to an adaptive state that develops after repeated drug use. Physical Dependence Body requires drug to maintain normal function. Sudden withdrawal → withdrawal syndrome (e.g., tremors, seizures, sweating, pain). Example: opioids, benzodiazepines. Psychological Dependence Emotional craving and compulsive drug use for pleasure or relief. Example: cocaine, cannabis, alcohol. 👉 Dependence is different from addiction. Addiction = compulsive harmful use; dependence may occur even with prescribed drugs. Tachyphylaxis Definition : Rapid development of tolerance when drug is given repeatedly in a short period. Onset : occurs within minutes or hours. Mechanism : depletion of neurotransmitter stores, receptor desensitization. Examples : Ephedrine: repeated doses lose effect due to depletion of noradrenaline. Tyramine: similar rapid loss of response.

12. Idiosyncrasy Definition : An abnormal, unusual, or genetically determined reaction to a drug in a small proportion of individuals. Not related to dose or drug’s usual pharmacological action. Examples : Chloramphenicol → aplastic anemia in some individuals. Primaquine → hemolysis in G6PD deficient patients. Barbiturates → excitement instead of sedation in some people. Cause : genetic variations in enzymes, receptors, or metabolism. Drug Allergy (Hypersensitivity Reaction) Definition : An immunologically mediated abnormal response to a drug. Occurs in sensitized individuals on re-exposure. Unrelated to dose or pharmacological action. Can range from mild rash to life-threatening anaphylaxis. Types of Allergic Reactions Immediate (Type I) : IgE mediated, occurs within minutes. Example: anaphylaxis with penicillin. Cytotoxic (Type II) : antibody-mediated cell lysis. Example: hemolysis with methyldopa. Immune complex (Type III) : serum sickness. Delayed (Type IV) : T-cell mediated, occurs after 24–48 hrs. Example: contact dermatitis with topical drugs.