rei
Forum Elite
Topics: 67
Posts: 126
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can anyone please explain why drug with high extraction ratio, the amount of drug extracted will depend on total liver blood flow; while for drug with low extraction ratio, the amount of drug extracted will depend on liver enzyme activity???
thanks in advance
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| milee99
Forum Guru
Topics: 48
Posts: 1,076
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for drugs with high hepatic extraction ratio (means that the enzymes in liver metabolise almost all of the drug that it gets , efficient metabolising system)--->if blood flow increases , the amount of drug going to the liver increases---->amount of drug extracted (means cleared by metabolism by liver) increases (since liver enzyme system is efficient enough to handle the increased drug load)
for drugs with low extraction ratios (means enzyme activity in liver is not efficient enough to metabolise all the drug amt that it receives ):
imagine hepatic blood flow is minimal, and enzyme activity is clearing all the drug it is receiving at this blood flow .. but this is maximal drug amt that it can handle .
if hepatic blood flow increases--->more drug is delivered to liver--->but enzyme activity is already at its maximal--->so same amt of drug is metabolised as previously ..hence , if drug extraction ratio is low, extraction depends on liver enzyme activity for that drug and is independent of blood flow to liver
read hepatic clearance from the following link:
http://www.boomer.org/c/p1/Ch17/Ch1704.html
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