Bioavailability (BA)

[poodle448]

I was just reading today on bioavailability (finally) and I'm very confused. I understand what it means, but would it mean we take much more of a drug than we need to? For example, DXM. The bioavailability of DXM is 11%. I did the math and 11% of a bottle of Robitussin (345mg) would be 37.95; Would this mean that it only really takes 37.95mg from the whole 345 to feel the effects?

I really hope somebody understands what I'm getting at here.8(

 

[pasha]

Homeless -> Other Drugs

 

[poodle448]

Homeless -> Other Drugs

I don't know that I agree that it's other drugs. I'm not talking about a drug. I'm talking about science behind all drugs.

 

[Downloader08]

Bioavailability is the 'availability' of a drug when it is administered in a certain way. When you orally take DXM not all of it is absorbed, or some is rapidly broken down by enzymes in various tissues and organs.
While I haven't checked out the BA of DXM, assuming BA is 11% orally then yes, 37.95mg is doing all the work. However in order for that amount to get into your system to do it's job, you must consume 345mg. So in this case there's a lot of 'wastage'.
Different routes of administration have different degrees of bioavailability depending on the molecule in question, IV is the easiest way to get 100% as all the drug is introduced into the blood stream at once.
That being said, it's not necessarily a good idea to IV DXM haha

 

[poodle448]

Bioavailability is the 'availability' of a drug when it is administered in a certain way. When you orally take DXM not all of it is absorbed, or some is rapidly broken down by enzymes in various tissues and organs.
While I haven't checked out the BA of DXM, assuming BA is 11% orally then yes, 37.95mg is doing all the work. However in order for that amount to get into your system to do it's job, you must consume 345mg. So in this case there's a lot of 'wastage'.
Different routes of administration have different degrees of bioavailability depending on the molecule in question, IV is the easiest way to get 100% as all the drug is introduced into the blood stream at once.
That being said, it's not necessarily a good idea to IV DXM haha

Thank you, this answered my question exactly! I don't plan on using an IV with DXM. I was only using DXM as an example because I knew the BA of it by heart.

On a side note... Is it possible to consume DXM powder via Insufflation?

 

[Downloader08]

I imagine it would be. Obviously it would only be a good idea if you had pure powder and even then I can't imagine the bioavailability would be that much better to warrant intranasal use. For some reason I believe that it's a pretty painful substance to snort (no sources- May have just read that somewhere).

In any case, to optimize nasal delivery of DXM you'd probably have to create some kind of vehicle (ie nasal spray) to make it worthwhile.

 

[sekio]

DXM can only be effectively delivered orally, it burns like a sonuvabitch if you attempt to snort it... (and has low water solubility to boot.)

I think DXM syrup and gels have a slightly higher BA than pure DXM when administered orally, but I have no way of proving it.

 

[Rybee]

Yes you're right OP, I think Morphine is a good example. The terminology and accuracy is obviously toned down a little bit to help demonstrate:

IV = ~100% bioavailability, thus 10mg Morphine via IV = ~10mg in your system
Rectal = ~40-70% bioavailability, thus ~10mg Morphine via Rectal = ~4mg-7mg in your system
Oral = ~20-40% bioavailability, thus ~10mg Morphine via Oral = ~ 2mg-4mg in your system

Since rectal administration has a higher bioavailability than oral administration, some folks prefer to administer it rectally because they get more bang for their buck.

If they want 10mg in their system, they can either inject ~10mg intravenously, plug ~20mg rectally, or take ~30mg orally.

I used to plug my Morphine because it made my prescription go further.

That said, you also have to take into account that the duration of action differs with each route of administration. So whilst IV might be good for short-term pain relief, Oral may be better for long-term pain relief.

As said, that's very dumbed down and there's a lot more to it (to which I wouldn't claim to fully understand) but I hope it helps reinforce what you're thinking?

 

[pasha]

I don't know that I agree that it's other drugs.

Feel free to delete your thread or ask for it to be moved. Bioavailability is a term which is bond to the fundamentals of pharmacokinetics of all drugs. It's not exclusive to any certain drug and obviously, neither are the drug discussion sections.