--you want to take that additional B12 on an empty stomach, apart from any other vitamins you are taking.

The cobalamin molecule is the largest molecule that the human body regularly uses, and it doesn't take much to interfere with its passive absorption through mucosal surfaces, which is what one is trying to accomplish by taking 1000mcg/day or more of B12 (since the daily "need" is more in the 8mcg range, one is trying to fulfill this through 1-2% passive absorption mechanisms--fortunately, B12 is inexpensive, and has no known toxicity level).