You are giving some one a drug, say, penicillin G, and you inject i.v. and you inject a total of 1 g. What would you think the plasma concentration is going to (make it in terms of g/L). Give me your thoughts as a Comment below.
Whatever you guestimate, would it be the same answer if you gave the drug orally?
Don't be afraid to give a wrong answer - I won't remember within a day who said what!
I'm pretty sure that, if given orally, the answer will be less than if it's given via i.v. injection. My guesstimate for the plasma concentration after i.v. injection is PC = dose/AVD, so PC = 1g/50L = 0.02 g/L. I said 50L because I read via the web that penicillin distributes throughout the body. Hopefully I was close...
ReplyDeleteI wrote this question a bit late and so we actually talked about this in class: Most students, on their first try, think about the plasma volume, about 3 L, and come up with the answer of "0.3 g/L" - and that is close to correct only for a little moment following rapid i.v administration plus the few seconds for mixing of blood (about 3 circulations). Beyond that there will be distribution and elimination determining the plasma concentration - until we reach the "elimination only" phase that would be linear on a semi-log plot. And for any further calculations we need of course the "volume of distribution".
ReplyDeleteCongratulations for at least giving it a try Courtney!