None of the B12 gets lost in the digestive process
observed that better outcomes (mortality, infection/complication rate, functional outcome score) were associated with early refeeding, a combination of parenteral and enteral nutrition, and immune enhancing formulas supplemented with a combination of probiotics, glutamine, arginine, fats (saturated and poly unsaturated, omega-3 fatty acids), protein, vitamins and minerals [114,115,116,117]
Front Neurol 9:802 Hussein AM, Eldosoky M, El-Shafey M et al (2019) Effects of GLP-1 receptor activation on a pentylenetetrazole-kindling rat model [J]
How long this lasts depends on how well the patient responds and the severity of the deficiency
doi:10.1542/peds.96.1.155