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Lec 1& 2
 

Lec 1& 2

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pharmacology lec1 and 2

pharmacology lec1 and 2

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    Lec 1& 2 Lec 1& 2 Presentation Transcript

    • Please, shut down your mobile
    • Faculty of Pharmacy
      Department of Pharmacology
      pharmacology
      General Pharmacology
      3rd year pharmacy students
      By
      “Dr. Shimaa Elshazly”
    • What is pharmacology?
      The term pharmacology comes from the Greek words:
      •Pharmakon- drug or medicine
      •Logos- the truth about or a rational discussion
      …………Truth about medicine
      • Pharmacology is the study of how
      drugs exert their effects on living
      systems.
      • More specifically it is the study of
      the interactions between a living
      organism and drugs that alter normal
      biochemical function.
    • History of Pharmacology
      Early pharmacology
      focused on natural
      substances, mainly plant
      extracts.
    • Modern approach
      • Pharmacology is a discipline as a bridge, not only to connect pharmacy with medicine, but also to link foundational medicine to clinical medicine
      Foundational Medicine
      Clinical Medicine
      Pharmacology
      Medicine
      Pharmacy
      Manufacture of Drugs
      Research of Drugs
    • ……..Subdivisions of Pharmacology
      • Clinical Pharmacology:
      application of pharmacodynamics and pharmacokinetics to human.
      •Toxicology -Study of
      harmful effects of drug
      •Posology- How medicines are
      dosed or calculation of dose
      •Pharmacognosy-
      Development of medicinal
      substances obtained from
      plants
    • Division of Pharmacology:
      • The science of pharmacology is divided into TWO important and interrelated areas :
      Pharmacokinetics: Study of the absorption,
      distribution, metabolism and excretion of drugs
      (ADME).
      ……………..what the body does to the drug
      B. Pharmacodynamics: Study of the molecular,
      biochemical and physiology effects of drugs on
      cellular systems and their mechanisms of action.
      ……………..what the drug does to the body
    • What Is a Drug?
      • A drug is a substance which when given to a patient can affect his body functions. This effect is useful in the treatment of a disease ( therapeutic ).If given in high dose it may cause a disease due to the toxicity of the drug itself.
      In other meaning:
      • Chemical agents used in the diagnosis, treatment, or prevention of disease
    • What are the sources of a drug?
      1- Natural
      2- Semisynthetic
      3- Purely synthetic
      4.Mineral Origin
      5.Genetic Engineering
    • 1- Natural:
      Plant Origin: eg.Atropine from belladonna & Morphine from Opium.
      b) Animal Origin: eg. Insulin, calcitonin etc.
      2- Semisynthetic:
      • These are compounds that are obtained from natural source and subjected to chemical modification eg.Penicillins and heroin (prepared by acetylation of morphine).
      3- Purely synthetic:
      • Are purely chemically synthesized. eg. The majority of drugs.
    • 4.Mineral Origin:
      eg. Iodine, magnesium sulphate
      5.Genetic Engineering:
      a) Gene Therapy.
      b) Recombinant DNA as the production of human insulin from bacterial origin.
    • Pharmacokinetics of drugs
      (ADME)
      ……………..what the body does to the drug
      Are studies of:
      • Absorption
      • Distribution or Disposition
      • Metabolism
      • Excretion or Eliminationof drugs
    • Drug Absorption
      • Absorption is the movement of a drug from its site of application into the blood or lymphatic system without being chemically altered
      • Mathematically it is define in terms of Bioavailability (Rate
      and extent of absorption).
    • Bioavailability
      Definition: Rate and extent of absorption
      i.e. Ka (Absorption constant)………. Rate of absorption.
      Area under curve (AUC)………. extent of absorption.
      • for i.v.: 100%
      • for non i.v.: ranges from 0-100%
      e.g. lidocaine bioavailability is 35% due to destruction in gastric acid and liver metabolism
    • Process of Absorption
      In order for a drug to be absorbed, it must be able to
      pass through cell membranes (which is a lipid
      barrier)
      • Lipid soluble drugs would be ideal to pass through the
      membrane easily.
      • Drugs can be absorbed by 4 main ways :
      1. Simple diffusion = passive diffusion.
      2. Active transport.
      3. Facilitated diffusion.
      4. Pinocytosis (Endocytosis).
    • Cell membrane
    • Simple or passive diffusion
      • Water soluble drug (ionized or polar) is readily absorbed via aqueous channels or pores in cell membrane.
      • Lipid soluble drug (nonionized or non polar) is readily absorbed via cell membrane itself.
    • Simple diffusion
      Characters
      • common.
      • Occurs along concentration gradient. Non selective
      • Not saturable
      • Requires no energy
      • No carrier is needed
      • Depends on lipid solubility.
    • Simple diffusion
      Low conc
      High conc
    • Simple diffusion
      Drugs exist in two forms ionized (water soluble) & nonionized forms (lipid soluble) in equilibrium.
      Drug ionized + nonionized
      Only nonionized form is absorbable.
    • Six things influence the rateof diffusion
      • Concentration gradientBig concentration difference (Fick’s Law) increasediffusion.
      • Size of molecule involved Large molecules slowdiffusion
      • Distance the molecule has to travelShort distance increase diffusion
      • TemperatureHigh temperatures increasediffusion
      • Solubility of the molecule
      • Surface area of the membrane over which the molecule can work.Large surface area increase diffusion
    • Active Transport
      • Relatively unusual.
      • Occurs against concentration gradient.
      • Requires carrier and energy.
      • Specific
      • Saturable.
      • Iron absorption.
      • Uptake of levodopa by brain.
    • Carrier-mediated Facilitated Diffusion
      • Occurs along concentration gradient.
      • Requires carriers
      • Selective.
      • Saturable.
      • No energy is required.
      • Selection is by size; shape; charge.
      • Common molecules entering/leaving cells this way include glucose and amino-acids.
    • Phagocytosis (Endocytosis & Exocytosis)
      Endocytosis: uptake of membrane-bound particles.
      Exocytosis: expulsion of membrane-bound particles.
      High molecular weight drugs or
      Highly lipid insoluble drugs
    • Factors which influence the rate of absorption:
      – Routes of drug administration
      – The physicochemical properties of the drug
      – Dosage forms
      – Circulation at the site of absorption
      – Concentration of the drug
    • Routes of drug administration
      Enteral
      via gastrointestinal tract (GIT).
      Oral
      Sublingual
      Rectal
      Parenteral administration = injections.
      Topical application
      Inhalation
    • Oral administration
    • First pass Metabolism
      Metabolism of drug in the gut wall or portal
      circulation before reaching systemic circulation
      So the amount reaching system circulation is less than the amount absorbed
      Where ?
      • Liver
      • Gut wall
      • Gut Lumen
      Result ?
      • Low bioavailability.
      • Short duration of action (t ½).
    • First pass effect
    • Dosage forms
      Capsules
      Tablets
      Syrup
      Suspension
      Hard- gelatin capsule
      Soft- gelatin capsule
      Tablets
      Spansule
    • Sublingual
    • Rectal administration
    • Parenteral administration
      Intradermal (I.D.) (into skin)
      Subcutaneous (S.C.)
      Intramuscular (I.M.)
      Intravenous (I.V.) (into veins)
      Intra-arterial (I.A.) (into arteries)
      Intrathecal (I.T.) (cerebrospinal fluids )
      Intraperitoneal (I.P.) (peritoneal cavity)
      Intra - articular (Synovial fluids)
      Intracardial
    • Parenteral administration
    • Ampoule Vial
    • 1- Intravenous ( IV )
      • The drug is injected right into the venous blood.
      Advantages:
      • Immediate effect.
      • Suitable for drugs not absorbed by the gut.
      • Rapidly destroyed drugs, short t½ can be infused continuously to provide a steady state of plasma concentration
      Disadvantages:
      • Dangerous if given rapidly.
      • Prolonged infusion of irritant drugs lead to venous thrombosis.
      • Susceptibility to infection if not using aseptic conditions.
    • 2- Intramuscular
      • Injection is made into a large muscle
      Advantages:
      • Reliable & produces more rapid absorption than SC.
      • Could be used for irritant drugs.
      • Could be used for depot preparations eg. Long actingpenicillins.
      Disadvantages:
      • It is painful.
      • Not accepted as self administration.
      • Risk of infection & formation of abscess.
    • 3- Subcutaneous (SC)
      Just under the skin
      Advantages
      • Can be given by the patient
      • Slow to obtain sustained drug effect eg. Insulin but generally complete
      • Suitable only for nonirritant drugs.
      Disadvantages
      • Large volume may be painful.
      • Tissue damage from irritant drugs
      • Maximum of 2 ml injection
      • Heat, Vasoconstrictors such as adrenaline greatly decrease the rate of absorption.
    • Produce local effect to:
      • Skin (percutaneous) e.g. allergy testing, topical local anesthesia
      • Mucous membrane of respiratory tract (Inhalation) e.g. asthma
      • Eye drops e.g. conjunctivitis
      • Ear drops e.g. otitis externa
      • Intranasal, e.g. decongestant nasal spray
      Topical application
    • Inhalation
    • Nebulizer Atomizer
    • Transdermal delivery system (TDS)
      TDS is a method by which the drug is released
      and absorbed through the skin for systemic
      absorption by a medicated adhesive patch
      applied to skin
      * Slow effect (prolonged drug action)
      e.g. the nicotine patches
      Advantages:
      • Lead to more stable drug level in the blood.
      • Avoid inactivation by first hepatic bypass eg. Nitroglycerine
      • Minimal side effects.
    • Factors which influence the rate of absorption:
      – Routes of drug administration
      –The physicochemical properties of the drug
      – Dosage forms
      – Circulation at the site of absorption
      – Concentration of the drug
    • Factor affecting absorption……
      Physico-chemical properties of drug
      • Molecular weight
      · Drugs with a small M.W. are absorbed well
      · Drugs which are large (often proteins) are absorbed poorly.
      • Chemical and enzymatic stability
      · The drug should be stable in gastric acid and in gut enzymes.
      e.g. Penicillin G is highly acid labile, or unstable in acid.
      • Aqueous and lipid solubility
      · For better absorption a drug must have optimum water and lipid solubility or a optimum partition coefficient. If it is highly lipid soluble it would not dissociate in the circulation i.e. Ion trapping. On the other hand, if it is highly water soluble then it will not cross the biological membrane.
    • Factor affecting absorption……
      pH and lipid solubility:
      Most drugs are either weak acids or weak bases and can exist in
      either the ionised (less lipid soluble) or unionised (more lipid
      soluble) form depending on the pH of the surrounding environment.
      REMEMBER THAT A DRUG IS ABSORBED BETTER IN THE
      UNIONISED FORM (Lipophillic drug can cross cell membrane)
    • Ion Trapping
      Body fluids where a pH difference will favor trapping of highly
      lipophillic drugs: e.g. Breast milk , Aqueous humor (eye) ,
      Vaginal secretions , Prostatic secretions
      • Aspirin is an acidic drug (pKa=5) and exist in the unionised form in stomach (pH 2.0)
      • In this form, it can enter the cells of the stomach lining (pH=7.4) where it is ionized and, in this form, it cannot leave the cell.
      • The concentration of ionized aspirin inside the cell continues to rise until it saturates and precipitates as crystals, which lead to gastric bleeding.
    • Factors which influence the rate of absorption:
      – Routes of drug administration
      – The physicochemical properties of the drug
      – Dosage forms
      – Circulation at the site of absorption
      – Concentration of the drug
    • Drug dosage forms
      • Different dosage forms have different rate and extent of absorption.
      • A syrup has fast rate of absorption as compare to tablet
      • A capsule has fast rate of absorption than tablet
      • Controlled-release, timed-release, sustained-release dosage form have a uniform absorption and less side effects
    • Thank you