When i used to work in a clinic setting they had a huge reference
On drug pharmacology for hospital use . When this book was replaced some of us got to have the older version to take
Home. It 's exact title escapes me here on vacation -- something
Like JHCP or something like that-- the B 12 excretion data
Was for the injections only and mentioned the 72 hrs.
This is probably why people who come here getting shots
Once a month complain of significant let downs days after
The monthly dose.

The effects of oral would be smaller but still will show in
The serum as artificial elevations to some extent.

Doctors know very little pharmacology about the drugs
They prescribe... And little to nothing about vitamins as
A rule. A good test is to ask what B2 is. You will get
The same blank look most Likely.(it is riboflavin).

500 is not a good result. Most of us here want 1000 pg/ml.