Does anyone know the absorption rate of b12 injections?

[Flinder]

Some websites said 1% for tablets. But I can’t find any website gives any absorption rate of injections.

[Foggyme Administrator]

The absorption rate from B12 injections is 100%. This is because it’s injected directly into the body rather than absorbed through the GI tract.

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[helvella]

As I understand, 1% absorption of oral B12 is a maximum. Actually, a maximum of 10 micrograms which equates to 1% of a 1000 microgram tablet. If you don't produce Intrinsic Factor, etc., it will effectively be zero.

[Gambit62 Administrator in reply to helvella]

helvella the 1% isn't a maximum - its an average - and actually the average is just below 1% - I haven't looked recently enough at the studies to know exactly how much variation there was in the range Its also just the average for passive absorption (outside the ileum)

There is a maximum absorption capacity for absorption in the ileum (the mechanism used in healthy individuals) - can't quite remember what it is - bit I'm pretty sure it is somewhere around 10mcg - but that doesn't apply if you have an absorption problem

[Flinder in reply to Gambit62]

10 mcg = 1% of 1000 mcg?

[Gambit62 Administrator in reply to Flinder]

red herring/co-incidence. Someone without an absorption problem would absorb 19.9mcg from a 1000mcg tablet (assuming normal absorption maximum is 10mcg

would absorb (in ileum) 10mcg

passively in rest of gut 1% of 990mcg = 9.9 mcg

total 19.9mcg

As earlier - not sure that the maximum absorption in the ileum is exactly 10mcg but its somewhere in that region

[helvella in reply to Gambit62]

I am not wholly convinced of the 9.9 microgram passive absorption.

If there were the case, we are back to asking why oral supplements are not sufficient for Pernicious Anaemia?

Or do you mean that B12 that has been Intrinsic Factor bound is passively absorbed?

[fbirder in reply to helvella]

No. The story is that 1% of an oral dose is absorbed passively. Then there's the story that 1% can be absorbed sublingually.

There have been no good studies to prove this. That's why Dr Hajo Auwerda, at a PAS conference described those studies as "stupid". It is why the PAS are helping in a study to measure oral absorption in people with PA. It is the reason why so many PA sufferers are being fobbed off with ineffective tablets.

Strangely enough, the amount that can be absorbed from an oral dose of 1000 mcg by somebody with a functioning IF system is about 13 mcg. Which is, by an amazing coincidence, almost exactly 1%.

When normal people take sublingual B12 they only absorb 1% of a 1000 mcg dose. Even though you'd expect them to absorb 3%.

When normal people take oral B12 they only absorb 1% of a 1000 mcg dose. Even though you'd expect them to absorb 2%.

The only logical conclusion is that people absorb 1% of a sublingual dose via the IF process and they absorb 1% of an oral dose via the IF process. Which would mean that passive diffusion must be zero.

If passive diffusion is real then we would all be taking B12 suppositories. The rectal membrane is just as permeable as the membrane of the mouth. The B12 in a suppository would be in contact with the membrane for hours, rather than minutes, and the amount absorbed is proportional to the time the drug is present. Instead of 1% absorption it would be closer to 50% absorption. A 1000 mcg suppository once a month would be more effective than a 1000 mcg injection every two months. But we don't use suppositories, because passive diffusion ain't real.

[fbirder in reply to helvella]

"do you mean that B12 that has been Intrinsic Factor bound is passively absorbed?"

No, that really is impossible. Passive diffusion only happen to small molecules. It's why the body needs an active process to absorb B12, because it is too large for passive diffusion. The IF-B12 complex is 40 times larger than B12 alone. So there is no way that it can undergo passive diffusion.

It's also why sublingual absorption can't happen. Saliva contains haptocorrin that binds to free B12, making a very large complex.

[helvella in reply to fbirder]

Yes - I agree.

I was trying to get to understand what was being suggested. If passive absorption were to result in 9 micrograms being absorbed, even without IF, then oral supplementation would suffice. And we know it doesn't.

Or you would have to explain why for those with PA are not able to absorb by passive diffusion.

[Gambit62 Administrator in reply to helvella]

Helvella, my understanding is that passive absorption is a completely different process from that involved in the ileum so it isn't dependent on IF - that is needed for the process in the ileum. However, 1% is very much an average and whilst some patients with PA do find a benefit from sublingual or high dose oral - others find no benefit - I find a benefit but I also use much more than 1000mcg.

The PAS is looking at working in partnership with a company wanting to look into licencing a pharmaceutical grade 1000mcg tablet.

It isn't clear why some benefit from passive absorption and others don't

[fbirder in reply to Gambit62]

Except that they don't absorb 20 mcg. They absorb about 13 mcg.

[helvella in reply to Gambit62]

You are, of course, right.