What is main organ for excretion?
Kidneys
Name other routes of excretion ( 6)
- Liver - into bile
- GI tract
- Lungs - gaseous anaesthetic
- Sweat
- Breast milk
- Saliva
What is enterohepatic reuptake
process whereby a drug or a metastable metabolite thereof in the liver is secreted into the bile, stored in the gall bladder, and subsequently released into the small intestine, where the drug can be reabsorbed back into circulation and subsequently returned to the liver.
What is Clearance
Sum of all elimination routes
Cl total =cl kidney +cl liver + cl other routes
What is clearance rate?
Amount of drug leaving body in a given time
Name factors for renal excretion? (7)
- Water soluble
- Small enough to fall through kidney glomerulus perforations
- Don’t rapidly diff into lipid membranes
- Present in significant quantities in blood/ plasma/ extra cellular fluid ( high vol distribution)
- Maybe filtered reabsorbed or excreted
- Depends on good kidney function
- Nutrients like glucose- filtered then quickly reabsorbed so not wasted
Factors for biliary excretion
- Maybe water sol and too big to pass through glomerular
- Maybe too lipophilic to be filtered without being reabsorbed again
- Some drugs transformed by metabolic processes
- Some excreted without being charged eg erythromycin or rifampicon
- Some enterohepatic reuptake - steroids, oral contraceptives
What is zero order excretion?
Rate of excretion of drug independent of its concentration
Can’t be influenced
Only few drugs eg ethanol- basis of breathalyser test
Phenytoin , fluoxetine, omeprazole
Plot of drug conc vs time - linear
Non linear kinetics
What is first order excretion
Rate of excretion directly proportional to its concentration
Most drugs
Plot of drug conc vs time is linear - linear kinetics
What is glomerular filtration
passive process that your kidneys use to filter excess fluid and waste products out of the blood into the urine collecting tubules of the kidney, so they may be eliminated from your body
Depends on hydrostatic pressure
Measure by GFR
( normal above 90 but probably ok over 50
What is tubular secretion
is the transfer of materials from capillaries to the renal tubular lumen
Often requires energy
Lipid sol ( un ionised drugs) - passive diffusion ie reabsorbed into bloodstream
Ionised will stay in urine
