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How is the BA of drugs determined?

KingBlueTwista

KingBlueTwista

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I am wondering how the bio-availability of drugs through various routes of administration is determined, because people seem to be so sure about this or that RoA being more/less effective, yet I have yet to see any statistical evidence for the facts spoken so confidently... obviously common sense dictates part of it, for example plugging your ears with xanax is probably a bad idea, but aside from the fact, where is the evidence? Anecdotal reports are too subjective to be reliably comparable... so yeah just hoping you could shed some light on it, cheers :)
By the way, awesome site guys, can't believe I just stumbled on it today. It's very well organised and everybody's so helpful.
 
I don't know whether it's done the same way for all drugs but I know that for some it's done by giving a set dose per kg by different routes and then measuring a number of levels over a period of time (how long it will take for levels to peak also varies by ROA). Sites like Medscape have a lot of data on this kind of stuff.
 
Since your post really asks a different question than the title, I'll answer the one in your post...

Whether or not someone can say honestly that one RoA will [probably] be superior to another depends on the drug... In some situations, take morphine for example, it is known that the oral route is widely varying in different individuals, but averages around 30%, while nasal administration is not wildly varying and is within a few percentage points of 10% absorption... In this case, it is obvious that oral is superior to nasal administration for most people... On the other hand, take oxycodone: Oral absorption is somewhere around 70-90%, while nasal is around 45%. While more may be absorbed by oral administration, it is not three times the amount absorbed through the nasal membranes, and so personal preference can easily go either way. Anyone who tries to say that one RoA is superior to another in this second example is not using the bioavailability figures correctly; while more may be absorbed orally, oral administration is also slower to get to peak plasma concentration and a marginally smaller dose absorbed more quickly through the nasal membranes is preferable to many.
 
enroll yourself in a phase I clinical trial and you'll find out. Be prepared to become a human pincushion.
 
Ohhh I think I see, so the speed at which a certain amount of the drug enters your system (and thus the intensity of the high) is not completely correlated to the overall bio-availability of the drug? Sorry if I'm a little slow, I've had a bucketful of clonazepam tonight. Thanks for the detailed reply, I'll be sure to re-read tomorrow when I'm not so fucked up.
I hope everyone on this forum is as informative as you are ;)
 
BA is determined relative to IV doses, which are always 100%. First, they give an IV dose to determine peak concentrations, AUC, and all that jazz.

Then, they give the dose another way (oral, IM, inhaled, rectal, etc) and measure the peak concentrations and AUC.

They plug that into a formula, and voila! BA determined
 
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