Your best insurance to protect yourself against such cases is to only accept injecting pure B12, mixed only with pure, preservative-free, sterile saline
International Diabetes Federation
High doses might also possibly interfere with levels of other vitamins, enzymes and minerals, which is always a potential problem when taking any nutrient in very large quantities
Difficulty walking, maintaining balance, and swollen, inflamed tongue: Difficulty with physical coordination can sometimes be caused by a deficiency of Vitamin B12
CTN can occur due to several causes, including trauma, infections (such as herpes zoster), multiple sclerosis, vascular compression, or iatrogenic injury from surgical procedures or dental work