I have just come across a German website B12-Vitamin.org ( b12-vitamin.com/ )
It makes interesting reading and appears to be very well researched and referenced. It suggests that for normal maintenance a dose of 500micrograms daily by mouth will allow sufficient passive absorption to meet the recommended daily intake of B12, even in the absence of intrinsic factor.
it seems to me that a large dose of B12 im or sub cut will automatically lead to asymptomatic peaks and horribly symptomatic troughs in blood levels of available B12. The recommended oral regime might ensure greater normalisation of blood and wellness levels.
I would welcome your thoughts.