Protein binding - Pharmacology

[jenn_rn_nj]

Hello -

Did a search and only found 2 old threads on the topic which did not address my question.

I understand protein binding / free drug. I believe that the bound drug and free drug exist in a 1:1 ratio (as free drug is "used up", bound drug becomes available to keep that balance). My question is if serum protein levels are low will the excess free drug be metabolized more quickly to reestablish a 1:1 ratio or will it be excreted to reestablish the 1:1 ratio?

Also, we were taught that lipid bound drugs remain in the body longer. Yet, I understand it works off the same principle - as free drug is used, then lipid bound drug is released to be metabolized...why does this remain in the body longer if the principle is the same? Is it merely longer to be distributed since it is not stored in the bloodstream like the protein bound drugs?

Hope the questions make sense and thanks in advance to anyone that can help. :)

[Adria, RN]

I can answer the question regarding drugs bound to protein in blood. If your serum protein levels are low then you are at risk for drug toxicity because the drugs will be metabolized and not excreted without being metabolized first. So your thought process regarding that was correct.

[Daytonite, BSN, RN]

this is the only site i could find on the general rate of metabolism of a drug that is protein bound. i think you'd have to look at the individual rates of metabolism for various drugs to determine how fast they unbind from their protein receptors. my sense is that the rapidity with which each drug unbinds and goes into a free state has to do with it's half life and is a characteristic of the drug. in any case, i found this information searching for pharmacokinetics on pharmacy school sites. it may not be specific enough for you, but my thinking is that if you can't find this answer on pharmacy school sites, it's unlikely it would be asked on a test for nursing school, don't you think?

http://www.pharmacy.umaryland.edu/courses/phar541-phar609/drug%20distribution/index.htm - pharmacokinetics on drug distribution. this is a powerpoint presentation on drug distribution and metabolism. call you attention to slide #9:

http://www.pharmacy.umaryland.edu/courses/phar541-phar609/drug%20distribution/sld009.htm - bound/unbound drug

but you might also want to look at the other slides in the presentation