Elimination Flashcards
(31 cards)
What is elimination the sum of?
Metabolism and excretion
Give an example of two drugs which are excreted largely unchanged
Benzylpenicilin and Gentamicin
What is the most important pathway for drug and metabolite excretion?
Renal excretion
Give 6 ways in which drugs and their metabolites can be excrete from the body
- Bile/Faeces
- Lungs
- Saliva
- Sweat
- Tears
- Milk
What is the calculation for renal excretion?
Renal excretion = (filtration + secretion) - reabsorption
What are the 4 stages in filtration at the nephron?
- Filtration
- Reabsorption
- Secretion
- Excretion
What sort of drugs are not filtered at the glomerulus?
Drugs bound to plasma proteins
What is the main determinant of whether or not a substance will be filtered by the glomerulus?
Molecular weight
What size of molecule is the glomerulus freely permeable to and what is the cut off point?
<2kDA
70kDa
What are the cells in the glomerulus called?
Podocytes
What are the arterioles that enter and exit the glomerulus called?
Afferent (entering)
Efferent (exiting)
Where are OAT and OCT systems located?
Proximal tubule and on the basolateral and apical surfaces of tubule epithelial cells
What are the 2 distinct steps in transporting substances from plasma into the lumen of the proximal tubule?
- Cellular uptake across the basolateral cell surface
2. Efflux into the tubule lumen across the apical surface
What provides the energy for transport of anions and cations across the tubule cells?
Ion gradients across the cell surfaces (Na+ gradient used to power anion transport across basolateral cell surface and cation transport across apical surface)
What are OATs responsible for?
Secretion of anionic drugs such as benzylpeniilin, methotraxate and ibuprofen, as well as phase two metabolites such as glucuronide and suphates.
What are OCTs responsible for?
Renal excretion of weakly basic drugs such cimetidine and quinie
How can you remember that benzylpenecilin is directly excreted without being metabolised?
It could be collected, purified and reused
What does Probenecid do?
Blocks OATs by competing for transport and inhibiting the tubular secretory system responsible for secretion of weak acids, increases the half-life of penicillin
Why is urine produced so much slower than blood is filtered?
Reabsorption as filtrate passes down the nephron
How can lipophilic molecules be reabsorped?
Diffusing down the concentration gradient back into the blood
Which form of drugs are easily excreted?
Ionised form
What can affect the reabsorption of weak acids and bases?
pH of urine
What does an acidic urine favour?
Reabsorption of weak acids (less of the drug will be ionised)
Why doesn’t an alkaline urine result in more excretion?
More of the drug will be in the lipophilic unionised form
