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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