[usluipek]

Pls, Can someone explain why only free non-ionized drug contribute to drug concentration gradient?

 

[khanar]

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 this is not high yield for the USMLE

 

[usluipek]

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.

 

[usluipek]

By the way, where are you reading 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.

 

[esc90]

So what is the final answer then?

 

[khanar]

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.

 

[khanar]

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)