@burcidi-- I'm not a doctor and you should ask your doctor about this for the best advice.
The way I see it, too much of everything is bad. Even though vitamin B12 is water soluble, the amount of it in your bloodstream will go up if you take very high doses regularly. Plus, people with impaired kidney function may not be able to get rid of excess vitamin B12 as fast as it needs to be removed. So toxicity is definitely possible.
That being said, if you don't go over the daily recommended dose, I don't think you will experience toxicity. My wife had vitamin B12 toxicity several years ago, but it was due to vitamin B12 injections that she was getting to support her vegan diet. The only symptom she had was diarrhea.