Pharmacokinetics

Question 1

Definition

Answer 1

Study of how drugs enter the body, reach their site of action and are elimated by the body

ie. What the body does to the drug!

Question 2

Liberation

Answer 2

• Only applies to oral drugs
• Process by which a drug is released from its delivery device during digestion
  
  • tablet, capsule, etc
• Rate of liberation is determined by its composition
  
  • powder vs tablet

Question 3

Absorption

Answer 3

• How a drug enters the bloodstream
• Depends on:
  
  • route of entry
  • character of drug
• Factors affecting absorption:
  
  • pH of the drug
  • Lipid/water soluble
  • Surface area of the drug
  • Surface area of the absorping environment
  • Rate of blood flow
    
    • hypothermia
    • shock
  • Drug concentration
  • Design of the drug
  • Delivery route

Question 4

Distribution

Answer 4

• The distribution of a drug around the body’s bloodstream and cells
• Dependant on chemical properties of the drug and its ability to:
  
  • cross cell membranes
    
    • passive diffusion
    • diffusion through aqueous channel
    • facilitated diffusion with carrier proteins
    • active transport against concentration gradient with input of energy
  • penetrate capillaries
  • cross blood-brain barriers
  • cross the placenta
• Factors affecting distribution:
  
  • protein & tissue binding
  • perfusion status
  • vascular supply to the target tissue
  • blood pH
  • presence of other protein binding drugs
  • CNS blood brain barriers
  • placental barrier
  • competing tissues

Question 5

Metabolism

Answer 5

• How a drug is changed by the body
• Complex liver enzyme system converts lipid soluble drugs to water soluble metabolites
• easier to eliminate
• Drugs absorped via the GI tract enter the liver before entering the general circulation which can metabolize/inactivate drugs before they distribution throughout the body
  
  • good if drugs are harmful/potent
  • prevents drugs such as GTN being given orally

Question 6

Elimination

Answer 6

• How drugs are removed from the body after metabolism:
  
  • kidneys - urine
  • bile
  • expired air
  • sweat
  • tears
  • faeces
• Half-life is the amount of time required for elimination processes to reduce drug serum concentration by half