Pharmacology

Nota:

• Can be split into two groups: PHARMOKINETICS PHARMOCODYNAMICS 

1. PHARMOKINETICS
   1. The movement of drugs through the body
      1. 4 stages
         1. Absorption
            1. Heavily influenced by route of administration
               1. ENTERAL
                  1. VIA gastro-intestinal tract
                     1. Tablets, oral liquids
                        1. Travel through GI tract
                        2. Absorbed in small intestine
                     2. Stomach tubing
                     3. Absorbed across intestinal wall- enters hepatic portal
                        1. Blood vessel that conducts blood from GI to liver
                        2. First pass effect: METABOLISM
                           1. PARTIALLY broken down by liver, excreted into bile, back into GI tract
               2. Parenteral
                  1. Other than gastro-intestinal
                     1. Injections
                     2. Topical
            2. Tissue perfusion
               1. Affects rate of absorption
                  1. Vasoconstriction: decrease blood flow, decreased absorption
                  2. Vasodilation- increased blood flow, increased absorption
         2. Distribution
            1. where the drug can get to- often limited by chemical properties
               1. Movement through body fluids and tissues
                  1. Blood=WATER= mainly hydrophilic molecules can dissolve and be carried by the blood
                  2. Cell membranes=fat= lipophilc substances enter cells easier
         3. Metabolism
            1. what the body chemically does to the drug- denatured, activated- LIVER
               1. BIOTRANSFORMATION
                  1. All blood from intestines passes straight to liver
         4. Elimination
            1. How the drug leaves the body- faecal and urinary routes
               1. Excretion of waste products
   2. How the body affects the drug e.g. absorption
   3. BIOAVAILABILITY
      1. Amount of drug that reaches the blood stream
         1. Intravenous= 100%
         2. Oral Variable 0-100%
            1. Travel through GI tract
               1. Most absorbed in SI
2. PHARMOCODYNAMICS
   1. The response of the body to the drug
   2. How the drug affects the body
      1. Receptor mediated pharmocodynmics - bind to a cell

         Nota:

         • 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. 
         1. Agonist
            1. Substance mimics ligand, normal response from receptor binding
            2. Partial Agonist
               1. substance doesnt fit the active site as well as ligand, elicts partial affects
            3. DOWNREGULATION of receptors
         2. Antagonist
            1. substance reacts with receptor, prevents any response, effectively blocking receptor (INHIBITOR)
               1. Competitive
                  1. Competes with ligand for active site, drug concentration drops, drug effect wears off, back to normal - REVERSIBLE
               2. Non Competitive
                  1. Does not compete with ligand, binds at allosteric site- when filled alters shape of the active site, ligand can no longer bind
               3. Reversible
                  1. COMPETITIVE: effects reversed, drug effect wears off.
               4. Non Reversible
                  1. may bind to active site or allosteric site, bind permanently- effects are long lasting, no increase in ligand can have an effect.
            2. UPREGULATION of receptors
         3. To bind: MUST HAVE AFFINITY
            1. High Affinity: quick response following administration
               1. prolonged duration of effect
               2. drug more competitive
            2. Low Affinity : higher dose of drug to have an effect
      2. Non-receptor mediated pharmocodynmics
         1. Liquid paraffin
         2. Water
         3. Laxatives
         4. Antibiotics
         5. Antifungals
   3. Receptors
      1. Specificity
         1. A drugs ability to bind to a small number of receptors
            1. Reduces likelihood of side effects
            2. Improves safety of drugs
            3. Makes dose/effect more reliable
      2. E.G Opiates
         1. All over the body, morphine causes:
            1. Vomiting
               1. Respiratory distress
                  1. Constipation
                     1. Shivering
3. Legislation
   1. Categories of medicines
      1. POM-V
         1. Prescription only medicine
      2. POM-VPS
         1. Prescription only meds- vet, pharmacist, SQP
      3. NFA- VPS
         1. Non-food animal- vet, pharmacist, SQP
      4. AVM-GSL
         1. Authorised vet medicine- general sales list