Drug Distribution Flashcards
What must a drug do to be active in the body?
Move from circulation to tissues
What 7 things affect a drugs ability to move from the circulation to the tissues?
- Plasma protein binding
- Tissue perfusion
- Membrane characteristics
- Transport mechanisms
- Diseases
- Other drugs
- Elimination
What does the binding of a drug in the plasma do to it?
- Renders it inactive
What plasma protein do drugs commonly bind to
Albumin
What 5 things can the act of binding be affected by?
- Renal failure
- Hyperalbumaemia
- Pregnancy
- Other drugs
- Free unbound albumin
What proportion of protein must be bound to allow the saturability of binding to play a role?
- 90%
Why is it 90%?
- If the bound albumin is 98% and changes to 96% then is a 100% increase of active drug
What membrane characteristics can result in decreased drug distribution?
- Blood brain barrier
- Blood-testes/ovary barrier
What 3 mechanisms does excretion of the drug in the kidneys depend on?
- Glomerular filtration
- Passive tubular reabsorption
- Active tubular secretion
What is glomerular filtration with regards to drugs?
- Unbound drugs filtered at the glomerulus
How can glomerular filtration be affected?
- Size and charge of the drug
- Renal failure
- Bound to a protein
What is passive tubular reabsorption?
- When the filtrate from the glomerulus moves down the tubules its conc increases
- The body reabsorbs some of this drug through passive diffusion
What type of drugs ONLY can be reabsorbed this way?
Un-ionised
What condition can affect passive tubular reabsorption?
Renal failure
What is active tubular secretion with regards to drugs
- When some drugs are actively secreted into the proximal kidney tubules
