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 VetOne Cyanocobalamin Vitamin B 12 Sterile Solution, 1,000 mcg mL, 100 mL 100 mL Vitamin B 12 Injectable for Horses, Dogs and Cats 1000 mcg 250 ml VITA JEC Vitamin B12 for Dogs, Cats & Horses, 1000 mcg mL, 100 mL Easy Refills Chewy Rx