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Unit-1: General pharmacology :Introduction to pharmacology

  2. Definition of Pharmacology • Pharmacology is the science that deals with the study of drugs and their interaction with the living systems. • Pharmacology is the science of drugs (Greek: Pharmacon—drug; logos—discourse in). In a broad sense, it deals with interaction of exogenously administered chemical molecules with living systems, or any single chemical substance which can produce a biological response is a ‘drug’.
  3. • Drug (Drogue—a dry herb in French) is a substance used in the diagnosis, prevention or treatment of a disease. • WHO definition— “A drug is any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient.”
  4. • Pharmacodynamics is the study of the effects of the drugs on the body and their mechanisms of action, i.e. what the drug does to the body. • Pharmacokinetics is the study of the absorption, distribution, metabolism and excretion of drugs, i.e. what the body does to the drug (in Greek Kinesis = movement). • Pharmacoeconomics deals with the cost, i.e. economic aspects of drugs used therapeutically
  5. • Pharmacogenomics is a branch of pharmacogenetics which deals with the use of genetic information in selecting drugs for a person. • Pharmacoepidemiology is the study of both the useful and adverse effects of drugs on large numbers of people. • Pharmacovigilance is a branch of pharmacoepidemiology which deals with the epidemiologic study of adverse drug effects. • Toxicology deals with the adverse effects of drugs and also the study of poisons, i.e detection, preventionand treatment of poisonings. • Chemotherapy is the use of chemicals for the treatment of infections. The term now also includes the use of chemical compounds to treat malignancies.
  6. • Pharmacopoeia (in Greek Pharmacon = drug; poeia=to make) is the official publication containing a list of drugs and medicinal preparations approved for use, their formulae and other information needed to prepare a drug; their physical properties, tests for their identity, purity and potency. • Pharmacy is the science of identification, compounding and dispensing of drugs. It also includes collection, isolation, purification, synthesis and standardisation of medicinal substances.
  7. SOURCES OF DRUGS • The sources of drugs could be natural or synthetic • Natural sourcesDrugs can be obtained from: • 1. Plants,e.g. atropine,morphine, quinine, and digoxin. • 2. Animals, e.g. insulin, heparin, gonadotrophinsand antitoxicsera. • 3. Minerals, e.g. magnesium sulphate, aluminium hydroxide,iron, sulphur and radioactiveisotopes. • 4. Microorganisms—antibacterial agents are obtained from some bacteria and fungi. We thus have penicillin, cephalosporins,tetracyclinesand other antibiotics. • 5. Human—some drugs are obtained from human beings, e.g. immunoglobulins from blood, growth hormone from anterior pituitaryand chorionicgonadotrophinsfrom the urine of pregnantwomen. • Synthetic :Mostdrugs used now are synthetic,e.g. quinolones, omeprazole, neostigmine, sulfonamides.
  8. Routes of DrugAdministration • The routes can be broadly divided into: • Enteral • Parenteral • Local
  9. ENTERAL ROUTE (ORAL INGESTION) Advantages 1. Safest route 2. Most convenient 3. Most economical 4. Drugs can be self-administered 5. Non-invasive route.
  10. ENTERAL ROUTE (ORAL INGESTION) Disadvantages: 1. Onset of action is slower as absorption needs time. 2. Irritantand unpalatable drugs cannotbe administered. 3. Some drugs may not be absorbed due to certain physicaland chemical characteristics, e.g. streptomycin is not effective orally. 4. Irritation to the gastrointestinaltractmay lead to vomiting. 5. There may be irregularities in absorption. 6. Some drugs may be destroyed by gastric juices, e.g. insulin. 7. Oralpreparations cannotbe given to unconscious and uncooperativepatients. 8. Some drugs may undergo extensive firstpass metabolism in the liver.
  11. Enteric Coated Tablets Some tablets are coated with substances like cellulose-acetate, phthalate, gluten, etc. which are not digested by the gastric acid but get disintegrated in the alkaline juices of the intestine.This will: • prevent gastricirritation. • avoid destructionof the drug by the stomach. • provide higher concentration of the drug in the small intestine. • prolong the duration of action.
  12. • In newer controlled release formulations, the tablet is coated with a semipermeable membrane through which water enters and displaces the drug out. • Advantages • Frequency of administration may be reduced. • Therapeutic concentration may be maintained. • Disadvantages • There may be ‘failure of the preparation’ resulting in release of the entire amount of the drug in a short time, leading to toxicity. • Enteric coated tablets are more expensive.
  13. PARENTERAL ROUTE • Routes of administration other than the enteral (intestinal) route are known as parenteral routes. Here the drugs are directly delivered into tissue fluids or blood.
  14. Advantages ➢ Action is more rapid and predictable than oral administration. ➢ These routes can be employed in an unconscious or uncooperative patient. ➢Gastric irritants can be given parenterally and therefore irritation to the gastrointestinal tract can be avoided. ➢It can be used in patients with vomiting or those unable to swallow. ➢Digestion by the gastric and intestinal juices and the first pass metabolism are avoided. Therefore, in emergencies parenteral routes are very useful routes of drug administration as the action is rapid and predictable and are useful even in unconsciouspatients.
  15. Disadvantages ➢Intramuscular injection may be painful and may even result in an abscess. ➢ Irritant solutions can damage the nerve if injected near a nerve.
  16. Parenteral routes include: A. Injections B. Inhalation C. Transdermal route D. Transmucosal route.
  17. A. INJECTIONS 1. Intradermal :The drug is injected into the layers of the skin, (e.g. BCG vaccine, tests for allergy) or by multiple punctures of the epidermis through a drop of the drug, e.g. smallpox vaccine. 2. Subcutaneous (SC) Injection: Here the drug is deposited in the SC tissue, e.g. insulin, heparin. 3. Intramuscular (IM): Aqueous solution of the drug is injected into one of the large skeletal muscles—deltoid,triceps,gluteus or rectusfemoris. 4. Intravenous (IV): Here, the drug is injected into one of the superficial veins so that it directly reachesthe circulation and is immediately available for action.
  18. B. INHALATION Volatile liquids and gases are given by inhalation, e.g. general anesthetics. In addition, drugs can be administered as solid particles, i.e. solutions of drugs can be atomised and the fine droplets are inhaled as aerosol, e.g. salbutamol
  19. C. TRANSDERMAL Highly lipid soluble drugs can be applied over the skin for slow and prolonged absorption, e.g. nitroglycerine ointment in angina pectoris.
  20. D. TRANSMUCOSAL ROUTE ➢Drugs are absorbed across the mucous membranes. Transmucosal administration includes sublingual, nasal and rectal routes. ➢Sublingual Here, the tablet or pellet containing the drug is placed under the tongue. . As the drug dissolves, it is absorbed across the sublingual mucosa. The formulation should be lipid soluble, e.g. nitroglycerine, nifedipine.
  21. TOPICAL • Drugs may be applied on the skin for local action as ointment, cream, gel, powder, paste, etc. • Drugs may also be applied on the mucous membrane as in the eyes, ears and nose as ointment, drops and sprays. • Drugs may be administered as suppository for rectum • Pessaries are oval shaped tablets to be placed in the vagina to provide high local concentrations of the drug at the site, e.g. antifungal pessaries in vaginal candidiasis
  22. SPECIAL DRUG DELIVERY SYSTEMS • In order to improve drug delivery, to prolong the duration of action and thereby improve patient compliance, special drug delivery systems are being tried. Drug targeting, i.e. to deliver drugs at the site where it is required to act is also being aimed at, especially for anticancer drugs
  23. ➢Spare receptors: A certain number of receptors are “spare.” Spare receptors are receptors that exist in excess of those required to produce a full effect. ➢Addiction: Addiction is defined as a chronic, relapsing disorder characterized by compulsive drug seeking and use despite adverse consequences. ➢Tolerance: Tolerance is a person's diminished response to a drug, which occurs when the drug is used repeatedly and the body adapts to the continued presence of the drug. ➢Dependance: Dependence means that when a person stops using a drug, their body goes through “withdrawal”: a group of physical and mental symptoms that can range from mild to life-threatening ➢Tachphylaxis: Tachyphylaxis is the appearance of progressive decrease in response to a given dose. ➢Idiosyncrasy: Drug idiosyncrasy" refers to untoward reactions to drugs that occur in a small fraction of patients and have no obvious relationship to dose or duration of therapy. ➢Allergy: A drug allergy is the abnormal reaction of your immune system to a medication.