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Introductory lectures for pharmacy students
- 1. Introduction to Pharmacology Dr. AbubakarKabiru B.Pharm, MSc, PhD American International University West Africa, The Gambia Department of Pharmacy
- 2. Definitions • Pharmacology: thestudy of the interaction of drugs with living organisms. It also includes history, source, physicochemical properties, dosage forms, methods of administration, absorption, distribution mechanism of action, biotransformation, excretion, clinical uses and adverse effects of drugs. • Drugs: chemicals that alter the function of living organisms. Drugs are generally given for the diagnosis, prevention, control or cure of disease.
- 3. Definitions • Pharmacodynamics: thestudy of the biological and therapeutic effects of drugs (i.e, “what the drug does to the body”) • Pharmacokinetics: study of the absorption, distribution metabolism and excretion (ADME) of drugs (“i.e what the body does to the drug”) • Toxicology: the science of poisons. Many drugs in larger doses may act as poisons. Poisons are substances that cause harmful, dangerous or fatal symptoms in living substances
- 4. Sources of Drugs •Minerals: Liquid paraffin, magnesium sulfate, magnesium trisilicate, kaolin, etc. • Animals: Insulin, thyroid extract, heparin and antitoxin sera, etc. • Plants: Morphine, digoxin, atropine, castor oil, etc. • Synthetic source: Aspirin, sulphonamides, paracetamol, zidovudine, etc. • Micro organisms: Penicillin, streptomycin and many other antibiotics. • Genetic engineering: Human insulin, human growth hormone etc.
- 5. Pharmacodynamics Involves how thedrugs act on target cells to alter cellular function
- 6. Receptor and non-receptormechanisms • Receptors are protein molecules present either on the cell surface or within the cell, e.g. adrenergic receptors, cholinoceptors, insulin receptors, etc. • Most drugs act by interacting with a cellular component called a receptor. Some drugs act through simple physical or chemical reactions without interacting with any receptor.
- 7. Receptor and non-receptormechanisms • Endogenous neurotransmitters, hormones, autacoids and most drugs produce their effects by binding with their specific receptors • Aluminum hydroxide and magnesium trisilicate, which are used in the treatment of peptic ulcer disease, act via non-receptor mechanisms by neutralizing the gastric acid (chemical reaction)
- 8. Receptor and non-receptormechanisms • Many drugs are similar to or have similar chemical groups to the naturally occurring chemical and have the ability to bind onto a receptor where one of two things can happen - either the receptor will respond or it will be blocked. • A drug, which is able to fit onto a receptor, is said to have affinity for that receptor. • Efficacy is the ability of a drug to produce an effect at a receptor. • An agonist has both an affinity and efficacy whereas antagonist has affinity but not efficacy or intrinsic activity.
- 9. Agonist vs. Antagonist •When a drug is able to stimulate a receptor and produce an effect, it is known as an agonist and therefore mimics the endogenous transmitter. • When the drug blocks a receptor, it is known as an antagonist and therefore blocks the action of the endogenous transmitter (i.e. it will prevent the natural chemical from acting on the receptor). • However, as most drug binding is reversible, there will be competition between the drug and the natural chemical to the receptor.
- 11. Chemical Bonding • Theforces that attract the drug to its receptor are termed chemical bonds and they are: • Hydrogen • Ionic (between charged ions) • Covalent • Vander Waals Force (weakest) • Covalent bond is the strongest bond and the drug-receptor complex is usually irreversible.
- 12. Drug Receptor Complex •When first messengers like neurotransmitters, hormones, autacoids and most other drugs bind with their specific receptors, the drug receptor complex is formed • The drug receptor complex causes the synthesis and release of another intracellular molecule termed second messengers e.g. cyclic AMP, calcium, inositol triphosphate (IP3), etc. • These second messengers produce the molecular mechanism of drug action
- 14. Site of DrugAction • A drug may act: 1. Extracellularly e.g: osmotic diuretics, plasma expanders 2. On the cell surface e.g.: digitalis, penicillin, catecholamines 3. Intracellularly e.g.: anti-cancer drugs, steroid hormones
- 15. Dose Response Relationship •The amount of drug administered will determine the kind of response you get • Minimum dose: the smallest dose that can produce a therapeutic effect • Maximum dose: the largest dose that can be safely administered • Toxic dose: the amount of drug that can cause a harmful effect • Lethal dose: the amount of drug that can cause death
- 16. Therapeutic Index • Theratio of the dose that produces the desired therapeutic effect (effective dose) to the dose that produces a toxic effect (toxic dose) • Safer drugs have wider therapeutic windows (penicillin); drugs that require more frequent monitoring have narrow therapeutic windows (digoxin, warfarin)
- 17. Pharmacokinetics Deals with theabsorption, distribution, metabolism and excretion drugs in the body. “What the body does to the drug”
- 18. Absorption • The processby which a drug enters into the systemic circulation from the site of administration through a biological barrier • In the case of intravenous or intra-arterial administration, the drug bypasses rigorous absorption processes and enters into the circulation directly • Routes of administration: alimentary tract (enteral) and parenteral
- 19. Alimentary Tract 1. Buccalcavity: e.g. ondansetron ODT 2. Sublingual: e.g. nitrates 3. Oral: e.g. aspirin, alcohol 4. Rectum: e.g. PCM rectal suppositories, enemas
- 20. Enteral Routes ADVANTAGES • Safe •Convenient • Economical DISADVANTAGES • Slow onset of action • Irritant drugs cannot be administered this way • Not useful in vomiting and severe diarrhea • Gastric acid and digestive enzymes may destroy some drugs
- 21. Parenteral Routes 1. Intradermal:layers of the skin, e.g. B.C.G. vaccine 2. Subcutaneous: Non-irritant, into subcutaneous tissue, e.g. insulin 3. Intramuscular: Soluble substances, mild irritants, suspensions and colloids can be injected by this route. These injections can be given to deltoid or gluteal muscle 4. Intravenous: into veins 5. Intrathecal: subarachnoid space of spinal cord, e.g. anesthesia 6. Intraarticular: into joints, e.g. hydrocortisone
- 22. Parenteral Routes ADVANTAGES • Fastonset of action • Uniform rate of absorption • Can be given in critical condition • Can be given in large volumes DISADVANTAGES • Pain at injection site • Drug effect cannot be halted immediately • Trained professionals have to administer
- 23. Topical/Local Route • Applicationof a drug directly to the surface of the skin • Doesn’t reach systemic circulation in large quantities • Includes administration of drugs to any mucous membrane • Eye, nose, ears, vagina • Dusting powder, paste, lotion, drops, ointment, suppository for vagina, patches
- 24. Topical Route ADVANTAGES • Usefulfor the local delivery of agents, especially those which have toxic effects if administered systematically • Convenient to use and easy to apply • Avoidance of first pass metabolism DISADVANTAGES • Not absorbed via skin or mucous membranes • Possibility of local skin irritation • Contact dermatitis likely due to excipients
- 25. Inhalation Route • Usedfor gaseous and volatile agents and aerosols • Solids and liquids are excluded if particle size is larger than 20 microns • Administered as dry powders, and nebulized particles when sprayed as fine droplets get deposited over the mucous membrane producing local effects and may be absorbed for systemic effects • Salbutamol inhaler used in bronchial asthma and volatile general anesthetics
- 26. Inhalation Route ADVANTAGES • Fewersystemic side effects • Effective for patients with respiratory problems • Rapid onset of action DISADVANTAGES • Patient may have difficulty administering/measuring dose • Some require assembly • May cause irritation
- 28. Bioavailability • The rateand amount of drug that reaches the systemic circulation and is available at the site of action after nonvascular administration • When the drug is given IV, the bioavailability is 100% • The route of administration determines the period between administration and onset of action
- 29. Bioavailability • Drugs givenby mouth may be inactive for the following reasons: 1. Enzymatic degradation 2. Poor absorption through gastrointestinal tract e.g. aminoglycosides 3. Inactivation by liver e.g. during first passage through the liver before it reaches systemic circulation
- 30. First Pass Metabolism • Drugsthat are absorbed via the GIT are circulated to the liver first • Liver acts as a filter • Only part of the drug enters systematic circulation
- 31. Factors affecting absorption •Physio-chemical properties of drug • Gas > Liquid > Solid • Lipid Soluble > Water Soluble (Unionized > Ionized) • Nature of the dosage form • Small particles > Big particles • Pharmacogenetic factors • Disease states
- 32. Factors affecting absorption •Physiological factors 1. Administration without, with, or after food 2. Presence of other agents (vit C w/ iron vs. tetracyclines w/ antacids) 3. First pass effect 4. Surface area (vasculature): small intestine > stomach
- 33. Distribution • Penetration ofa drug to the sites of action through the walls of blood vessels from the administered site after absorption • Drugs distribute through various body fluid compartments such as: • (a) plasma • (b) interstitial fluid compartment • (c) trans-cellular compartment
- 34. Factors affecting distribution •Protein binding • Protein bound vs free drug • Plasma concentration • IV, falls sharply • Oral, rises and falls gradually • Sublingual, rises sharply and falls gradually • Clearance • Physiological barriers • Blood brain barrier (BBB) • Placenta
- 35.
- 36. Metabolism • Drugs arechemical substances, which interact with living organisms and produce some pharmacological effects • After, they should be eliminated from the body unchanged or changed to some easily excretable molecule • The chemical reactions involved in biotransformation are classified as Phase 1 and Phase 2 reactions
- 37. Phase 1 Reactions •Make the drug polar (water soluble) so it can be excreted via urine • Oxidation • Reduction • Hydrolysis • Typically involves the use of cytochrome P450 enzymes
- 38. Phase 2 Reactions •Some drugs may not be excretable after Phase 1 and will need to undergo further metabolism • Combines an endogenous substance with the drug (conjugation) • Glucuronidation • Methylation • Acetylation • Sulfation
- 39. Excretion • The transportationof unaltered or altered form of drug out of the body. • Major processes of excretion include renal excretion, hepatobiliary excretion and pulmonary excretion • Minor routes of excretion are saliva, sweat, tears, breast milk, vaginal fluid, nails and hair
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