1212 Week 14

1212 Week 14

1. Lecture 2

   • Definitions
     • Drug - chemical of known structure causes biological effect
     • Medicine - 1 or more drugs alongside other substances which are used theraputically
     • Pharmacology - study of drug action
     • Toxicology - study of the adverse effects of chemicals
     • Pharmacodynamics - what a drug does to the body
     • Pharmacokinetics - what the body does to the drug
   • ADME
     • A - absorption - getting the drug into the systemic blood system
     • D - distribution - getting the drug from the blood to the target tissue(s)
     • M - metabolism - breakdown of drug at action site
     • E - excrection - elimination of the drug from the body
     • determines the concentration of the drug at the target tissue which affects onset, intensity and duration of action
   • Drugs
     • classified by molecular structure, mode of action and theraputic use
     • given chemical, generic and brand names
   • Drug Administration
     • Enteral - administration via the GIT
     • Parenteral - administration not via the GIT
     • oral - most common method, onset 10-20 mins
     • dissolution rate is the rate limiting step and can be increased by increasing the drug's surface area
     • oral has to survive the gastric acid, digestive enzymes, gut bacteria and co-exist or avoid food
     • absorption of oral drugs is mainly transcellular passive diffusion so drugs have to be lipophilic
     • pH affects solubility and ionisation of drugs, only the unionised forms can be absorbed

2. Lecture 3

   • Routes of Drug Administration
     • Sublingual - absorption under tongue
       • no 1st pass effect
       • rapid onset
       • no large doses as small surface area
       • example - glyceryl trinitrate for angina
     • Rectal - absorbed through anus
       • good when oral route is comprimised
       • good when drug will damage the stomach lining
       • examples - paracetamol for pain relief, promethazine for nausea/motion sickness
     • IV - direct into the blood stream via a needle
       • 100% bioavailibility
       • requires supervised inpatient care
       • useful in emergencies
       • immediate onset
       • example - all drugs
     • Intramuscular/subcutaneous - drug injected into tissue matrix and absorbed into local vessels
       • fenestrations allow for paracellular diffusion
       • aqueous formulation allows fast onset
       • depot can be formed for gradual release
       • no first pass effect
       • requires supervision and is invasive and costly
       • example - insulin for diabetes
     • Inhalation - breathed into the lungs
       • large surface area
       • permeable
       • low metabolism
       • local effect
       • examples - anaesthetics, salbutamol for asthma
     • Intranasal - through the nose
       • rapid onset
       • no first pass effect
       • enables peptide aborption
       • allows drug to cross blood brain barrier
       • example - mometasone for hay fever
     • Topical - direct administration to action site (normally a cream)
       • delivery to eye, vagina and skin
       • local and targeted action
       • example - betamethasone diproprionate for eczema
     • Transdermal - patches applied to the skin
       • depot of drug
       • systemic absorption
       • have to be lipid soluble
       • example - nicotine for stopping smoking
   • Oral Drug Administration Mechanism
     • drugs diffuse into the intestinal cells and P-glycoproteins pump them back into the lumen using ATP
     • drugs absorbed via carrier mediated transport
     • L-DOPA is an amino acid that has to use a carrier protein, it is similar in structure to tyrosine so they use the same carrier protein
     • first pass effect - drainage of GIT capillaries goes to the liver to be filtered before entering the systemic circulation.
     • oral drugs have to survive the first pass effect