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Discussion Starter · #1 ·
Pls, Can someone explain why only free non-ionized drug contribute to drug concentration gradient?
 

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Only non-ionized drugs can cross lipid membranes.
Ionized drugs cannot cross lipid membranes and therefore they do not play role in the concentration gradient.

By the way, where are you reading :eek: this is not high yield for the USMLE
 

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Discussion Starter · #3 ·
Thanks for the explanation. But if an ionized drug does not cross membrane, it will accumulate outside of cell and will increase extracelluar concentration. I am still a little confused.
 

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Discussion Starter · #4 ·
By the way, where are you reading :eek: this is not high yield for the USMLE
I was going over concepts, and came across this question. May be USMLE will not ask this directly, but I think concept is important, especially for the first reading.
 

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I was going over concepts, and came across this question. May be USMLE will not ask this directly, but I think concept is important, especially for the first reading.
Yeah, this is a low yield concept and you should not waste your time with it.
 

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Thanks for the explanation. But if an ionized drug does not cross membrane, it will accumulate outside of cell and will increase extracelluar concentration. I am still a little confused.
The non-ionized will cross and then it will be ionized inside the cell (by the intracellular PH, depending if it was weak acid or base)
 
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