Pharmacokinetics

• Pharmacokinetics

  how the drug moves through the body
• Perfusion

  delivery of blood to an area

  the closer the capillaries are, the less distance there is to diffuse

  this can be affected by ischaemia or exercise
• When would we not want Rapid Absorption?

  when using slow release tablets

  topical medications

  local anaesthesia
• What are the Phases of a Metabolic Reaction?

  phase 1

  - original molecule is chemically transformed by oxidation, reduction and hydrolysis

  - metabolite formed

  - hydrophilic which alters bioactivity

  
  

  phase 2

  - metabolite combines with another

  - reduced bioactivity

  - easier excretion as more water soluble
• Transcellular

  involves the movement through cells
• Bioavailability

  the percentage of drug that reaches circulation when it has entered the body , this is how absorption is measured
• Steady State

  the drug concentration remains the same dose to dose
• First-pass Metabolism

  when a drug undergoes metabolism at a specific point in the body, this reduces drug concentration once it enters the systemic circulation or its site of action
• Volume of Distribution (Vd)

  used to estimate the extent of drug distribution from the blood to the tissues

  this is dependent on perfusion, capillary wall permeability and protein binding
• Biotransformation

  conversion from one chemical entity to another
• Paracellular

  the transport in between cells
• Therapeutic Range

  the ideal range of drug concentration in the body
• Lipophilic vs Hydrophilic

  lipophilic is non-ionised and non-polarised and dissolves readily in fat

  hydrophilic is ionised and polarised and dissolves readily in water
• Absorption


  this is dependent on the method of administration into the systemic circulation and varies with each drug
• Protein Plasma Binding

  albumin and globulin

  these bind to the drug to keep it in circulation, bound drugs are usually deactivated and are not metabolised or excreted
• Metabolism

  biotransformation occurs

  aids in detoxification and elimination

  mostly occurs in the liver
• Hepatic Excretion

  can either be metabolised in the liver or excreted straight into bile

  bile is excreted via the small intestines

  enterohepatic circulation can occur
• Factors that Affect Absorption

  pH of environment

  rate of administration

  tissue perfusion

  lipophilic:hydrophilic nature

  method of crossing membranes
• What are the 4 Steps of Pharmacokinetics?

  absorption, distribution, metabolism, excretion
• Distribution


  getting the drug to the site it needs to be
• How can the pH of the environment affect the rate of administration?

  the pH of the environment can affect the lipophilic:hydrophilic ratio and can also affect the rate and method of crossing membranes. also, acid drugs become more lipophilic in acidic environments
• Pharmacology

  the study of chemicals (drugs) and how they interact with the body
• Carrier Proteins

  these are transmembrane and they bind to specific molecules, but, they are limited by the number of carriers
• Specific Barriers

  only small lipophilic molecules can pass as the capillary wall structure is less permeable
• Enterohepatic Circulation

  when the bile acid molecules from the liver travel to the intestines and then back to the liver
• What is the Importance of Enterohepatic Circulation?

  it allows for the recycling of metabolised and non-metabolised compounds and is important in toxicological processes that involve the GI tract
• Routes of Administration

  IV - 100% absorbed

  IM - quick absorption

  SC - slower absorption

  PO - must undergo dissolution, first-pass metabolism may occur and this is affected by the GI health
• Renal Excretion

  glomerular filtration

  passive tubular reabsorption

  active tubular secretion
• Enterohepatic recirculation occurs within which stage of the pharmacokinetics of a drug?

  excretion
• How is the elimination rate of a drug measured?

  half-life
• How many half-lives would it generally take to reach a steady state of 95%

  5
• Half-life


  the time is takes for the amount of a drugs active substance in the body to reduce by half