Can anyone explain why oxycodone has a higher oral bioavailability than intranasal, and amphetamine has a higher intranasal bioavailability than oral (lots of other examples)? This has always been extremely confusing to me. What's the difference between the membranes in your nose and those in your stomach/intestine that accounts for this?

bioavailability means the percentage of the drug that is absorbed from administering it a particular way as opposed to other ways. some ways of using a drug help more of it absorb than other ways. use google next time please, and have a great day!;)

not positive about this, but i think it has something to do with the molecular structure and transport proteins.

We have a winner.

We have a winner.

That's not a winner at all! (no offense to kwerjack)
What exactly is it? Can anyone give me a good explanation?

well im not wrong, but i just didnt explain it thoroughly.

some drugs get absorbed and cross the BBB easier in the stomach and digestive track because they have different molecular structures which fit into transport proteins, while other drugs with different molecular structures dont, and some of it gets lost.

same goes with snorting, if a drug isnt fat/water soluble, your not gonna get high, or if it doesnt match with the TP's in the nose well, it has a low bioavailibility.

well im not wrong, but i just didnt explain it thoroughly.

some drugs get absorbed and cross the BBB easier in the stomach and digestive track because they have different molecular structures which fit into transport proteins, while other drugs with different molecular structures dont, and some of it gets lost.

same goes with snorting, if a drug isnt fat soluble, your not gonna get high, or if it doesnt match with the TP's in the nose well, it has a low bioavailibility.
Water soluble dude. Take cocaine for instance.

Water soluble dude. Take cocaine for instance.

Lipid soluble will work, too. http://www.panthrax.host.sk/snort_benzos.html