Drug Distribution Flashcards
Define drug distribution:
Reversible transfer of drug between blood/extravascular fluids and Tissues.
What effects tissue distribution of drug:
- Plasma binding Protein
- Tissue Perfusion
- Membrane characteristics
- Transport Mechanisms
- Effected by diseases & other drugs
- Elimination
What type of Membrane characteristics affect tissue distribution of drugs:
Blood-Brain barrier
Blood-Testes/Ovary barrier
Both resistant to many substances attempting to cross
What are plasma binding proteins?
PLasma proteins like albumin that bind to drugs making them biologically inactive
What effects the level of bound drug:
Renal Failure
Hypoalbuminemia
Pregnancy
Other drugs
Saturability of Binding
When is the level of bound drug relevant?
When above 90% of the drug is bound to plasma binding proteins
Why are high plasma protein binding levels imporant?
When the level of bound drug is say 98% a change to 96% is a 100% increase in active drug levels.
What 3 mechanisms affect renal drug excretion:
- Glomerular Filtration
- Passive Tubular Filtration
- Active Tubular Secretion
What is filtered at the glomerulus?
Unbound drugs
What about the drug can prevent glomerular filtration?
Drug particle size & charge
How does filtration rate affect drug clearance rate?
Increased filtration rate increases drug clearnacne rate
In passive tubular filtration how does drug conc change?
The further downt he kidney tubules the more concentrated the filtrate.
Therefore the drug is also more concentrated.
How happens to some of the drug in passive tubular filtraion?
Its reabsorbed by passive diffusion, only the unionised drug is reabsorbed
What does active tubular secretion mainly excrete?
Protein bound cationic (+ve) & anionic (-ve) drugs.
