Posted by Elizabeth on April 11, 2002, at 9:02:26
In reply to How to get a half-life..., posted by Adam on April 10, 2002, at 23:03:12
> I always think that any discussion of this kind benefits from some understanding of some simple math and physical principles.
Yes, that's my feeling. This isn't complicated stuff, although the inability to use proper notation on this board makes it look kind of messy and cluttered. Also, resorting to expressing stuff in terms of logs might be intimidating to some.
> You can, if you know the half-life, calculate the amount of drug you are going to have around at any point in the future. You can also determine the half life of something by watching it dissapear over any span of time.
This is true in some cases. I should point out, though, that with many drugs, the concentration isn't always the same in all parts of the body. (Adam mentions this at the end of his post but doesn't go into detail; personally I think it's pretty important, even more important than guppies -- maybe.) If you're dealing with a drug that occurs in different concentrations in different places, the elimination half-life isn't such a good model. If the concentration is the same everywhere, a "one-compartment model" is adequate. There are also two- and three-compartment models for calculating this kind of thing when the concentration isn't the same in different places; the "compartments" might be sites like the brain, for example (particularly important when dealing with psychoactive drugs).
> It doesn't make much sense, under normal circumstances, to talk about the half-life of guppies.
I dunno -- maybe in some models it does!
> The guppies swim along happily for however long their life span allows, and then, all of the sudden, they die.
> Now let's imagine a rather perverse scenerio
Ahh, my favorite kind.
You know, if yesterday someone told me that today I would read a post here in which someone compared medications to fish, I wouldn't have believed it.
-elizabeth
poster:Elizabeth
thread:101843
URL: http://www.dr-bob.org/babble/20020408/msgs/102738.html