Pharmacology

Pharmacology

1. PHARMOKINETICS

   • The movement of drugs through the body
     • 4 stages
       • Absorption
         • Heavily influenced by route of administration
           • ENTERAL
             • VIA gastro-intestinal tract
               • Tablets, oral liquids
                 • Travel through GI tract
                 • Absorbed in small intestine
               • Stomach tubing
               • Absorbed across intestinal wall- enters hepatic portal
                 • Blood vessel that conducts blood from GI to liver
                 • First pass effect: METABOLISM
                   • PARTIALLY broken down by liver, excreted into bile, back into GI tract
           • Parenteral
             • Other than gastro-intestinal
               • Injections
               • Topical
         • Tissue perfusion
           • Affects rate of absorption
             • Vasoconstriction: decrease blood flow, decreased absorption
             • Vasodilation- increased blood flow, increased absorption
       • Distribution
         • where the drug can get to- often limited by chemical properties
           • Movement through body fluids and tissues
             • Blood=WATER= mainly hydrophilic molecules can dissolve and be carried by the blood
             • Cell membranes=fat= lipophilc substances enter cells easier
       • Metabolism
         • what the body chemically does to the drug- denatured, activated- LIVER
           • BIOTRANSFORMATION
             • All blood from intestines passes straight to liver
       • Elimination
         • How the drug leaves the body- faecal and urinary routes
           • Excretion of waste products
   • How the body affects the drug e.g. absorption
   • BIOAVAILABILITY
     • Amount of drug that reaches the blood stream
       • Intravenous= 100%
       • Oral Variable 0-100%
         • Travel through GI tract
           • Most absorbed in SI

2. PHARMOCODYNAMICS

   • The response of the body to the drug
   • How the drug affects the body
     • Receptor mediated pharmocodynmics - bind to a cell
       • Protein based molecules present on cell membrane. ACTIVE SITE- LIGAND can bind- once filled with ligand the receptor triggers an effect e.g. opens ion channel. 
       • Agonist
         • Substance mimics ligand, normal response from receptor binding
         • Partial Agonist
           • substance doesnt fit the active site as well as ligand, elicts partial affects
         • DOWNREGULATION of receptors
       • Antagonist
         • substance reacts with receptor, prevents any response, effectively blocking receptor (INHIBITOR)
           • Competitive
             • Competes with ligand for active site, drug concentration drops, drug effect wears off, back to normal - REVERSIBLE
           • Non Competitive
             • Does not compete with ligand, binds at allosteric site- when filled alters shape of the active site, ligand can no longer bind
           • Reversible
             • COMPETITIVE: effects reversed, drug effect wears off.
           • Non Reversible
             • may bind to active site or allosteric site, bind permanently- effects are long lasting, no increase in ligand can have an effect.
         • UPREGULATION of receptors
       • To bind: MUST HAVE AFFINITY
         • High Affinity: quick response following administration
           • prolonged duration of effect
           • drug more competitive
         • Low Affinity : higher dose of drug to have an effect
     • Non-receptor mediated pharmocodynmics
       • Liquid paraffin
       • Water
       • Laxatives
       • Antibiotics
       • Antifungals
   • Receptors
     • Specificity
       • A drugs ability to bind to a small number of receptors
         • Reduces likelihood of side effects
         • Improves safety of drugs
         • Makes dose/effect more reliable
     • E.G Opiates
       • All over the body, morphine causes:
         • Vomiting
           • Respiratory distress
             • Constipation
               • Shivering

3. Legislation

   • Categories of medicines
     • POM-V
       • Prescription only medicine
     • POM-VPS
       • Prescription only meds- vet, pharmacist, SQP
     • NFA- VPS
       • Non-food animal- vet, pharmacist, SQP
     • AVM-GSL
       • Authorised vet medicine- general sales list