Why is drug clearance not affected by blood flow in case of low extraction ratios?

[myvow]

Background information:

1) Variation of organ blood flow:

a) for drugs with low extraction ratio (<0.3): the venous drug concentration is virtually identical to the arterial concentration and organ clearance is poorly influenced by blood flow variations.

b) for drugs with high extraction ratio (>0.7): changes in blood flow produce corresponding changes in clearance, e.g. an increase in organ blood flow will increase the amount of drug presented to and eliminated by the organ.

So my question: What is the reason that the clearance of drugs with low extraction ratios are not influenced by the variation of blood flow?

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[fhwulala]

Imagine two highways with identical number of cars,
one has numerous exits and the other has none.
Which one would have more variability in the number of cars?

 

[myvow]

Thank you.
And if I counter some problems from my textbook,is there a suitable place for asking?

 

[oldstock]

Thank you.
And if I counter some problems from my textbook,is there a suitable place for asking?

Try the Pharmacy forum.

 

[myvow]

Thank you for Your recommend