How do you manage B12 deficiency refractory to subcutaneous replacement?

I tend to start with IM injections of B12 when patients are severely deficient. The most common mistake in replacing severely low B12 is to not load, or to check levels too early. I have not used SQ administration before. It should absorb, but if you are having issues I would go to IM and start week...

Does the patient have subcutaneous edema?

I would administer IM unless there is a contraindication.