Ice crystal formation ruptures the molecular structure of both the water and benzyl alcohol, rendering the solution unusable
Reference: Kleinman HK & Sosne G (2012)
Moreover, it is generally suggested to give B12 in the morning or no later than 2pm to avoid potential sleep issues
If you follow a strict vegan or vegetarian diet, getting enough B12 from food alone can be a real challenge
These dosages are typically given to treat deficiency resulting from pernicious anemia, gastrointestinal disorders (such as Crohns disease), malabsorption syndromes, gastric surgeries and long-term use of medications (such as proton pump inhibitors)
Since B12 is not created by the human body, it can be supplemented via this method if your diet is insufficient