Giving vitamin B12 parenterally? Which electrolyte should you check first? Answer: Potassium. And why does it matter? Because rapid correction of severe B12 deficiency can trigger a surge in Vitamin B 12 Injectable for Horses, Dogs and Cats 1000 mcg 250 ml Sandoz Vitamin B12 Injectable Solution 1000 mcg 10 mL Vitamin B12 Vitamin B12 Cyanocobalamin Injection 1000 mcg mL 1 mL Med Plus Physician Supplies