help! plasma protein binding ? for pharm...

babynursewannab · Dec 12, 2004

okay...lets see...

Protein binding drugs have an affinity for albumin and such, right? While a drug is bound, it is not free-floating in the system, it is stuck up with something. (Still with me?)

Now, if there is not a lot of plasma protein, then less of the drug will get stuck (because there are less proteins to bind to) and it will leave more free-floating drug in the blood with no protein to call home. It is this free-floating drug that is fully used by the body.

Certain drugs rely on normal protein levels (understanding that much will be lost to protein binding) and when the protein levels are low, there is too much available drug in the system and normal administration levels could actually become toxic.

Does that help?

Good luck!

-Alyssa

snwflknurse · Dec 13, 2004

thanks alyssa! I've been at this studying all day. Less than 48 hours to pharm final...yikes. I love the way you explained this. Thank you SO much.

Good luck to you too!:)

Sarah

okay...lets see...
Protein binding drugs have an affinity for albumin and such, right? While a drug is bound, it is not free-floating in the system, it is stuck up with something. (Still with me?)
Now, if there is not a lot of plasma protein, then less of the drug will get stuck (because there are less proteins to bind to) and it will leave more free-floating drug in the blood with no protein to call home. It is this free-floating drug that is fully used by the body.
Certain drugs rely on normal protein levels (understanding that much will be lost to protein binding) and when the protein levels are low, there is too much available drug in the system and normal administration levels could actually become toxic.
Does that help?
Good luck!
-Alyssa

purplekath · Dec 13, 2004

Think of it this way (but remember it's simplified!) - there are two ways drug particles can travel in the system. One is bound to proteins (plasma), and one is floating as "free drug" - to be therapeutic, it's the "free drug" that does the work. Protein bound drug must go where the proteins go, so are of very little value therapeutically.

The more protein (plasma) you have in your system, the more proteins there are for the drug to attach to. This equals LESS "free drug" to do the work (curing the headache etc). So where protein levels are very high, you may have to give more drug to get to the levels of free drug that will work for your patient - this level is called "the minimum therapeutic level."

Conversely, if you have a condition where you have LESS proteins in your system (for example, burns patients will often lose a lot of plasma proteins), you will have MORE free drug in the system. Therefore you may have too much "free drug" in the system - far more than the body can use and excrete quickly enough. This makes the drug toxic in the body - in pharm this is called the "toxic level".

The difference between the "minimum therapeutic level" and the "toxic level" is called the "therapeutic range". This range is different for different people and different drugs. For some drugs, this range is very narrow (I think Gentamicin is one??), so you will be required to monitor blood levels regularly to ensure the drug doesn't become toxic. For some patients (such as children, or patients who have very little protein) then the range for some drugs will be narrower for that specific patient, so monitoring might also be necessary.

Hope that helps :-)

babynursewannab · Dec 13, 2004

Sarah-

No problem. Happy to help. You will see, when you are done and able to take a step away from all of this, a lot of the stressful stuff during pharm class is really not difficult at all. They just cram so much stuff into your brain at once that any information feels like it is attacking you! :chuckle

-Alyssa