The math itself is not complicated
Autoimmune neuropathies
Dugger and Dickson 2017).The group of neurodegenerative diseases includes a significant number of conditions, and Alzheimer's disease (AD), Parkinson's disease (PD), Multiple Sclerosis (MS), Amyotrophic Lateral Sclerosis (ALS) and Spinal Muscular Atrophy (SMA) are the main ones (Checkoway et al

For patients seeking weight loss who request B12 injections, GPs should: Assess for genuine deficiency through appropriate blood tests rather than empirical treatment Provide education about the lack of evidence supporting B12 for weight loss in non-deficient individuals Explore underlying concerns about weight and energy levels, addressing these through appropriate channels Signpost to evidence-based resources such as NHS weight management services according to local pathways Patients should contact their GP if they experience unexplained fatigue, neurological symptoms (numbness, tingling, balance problems), or signs of anaemia (pallor, breathlessness, palpitations), as these may indicate B12 deficiency requiring investigation
You would then use a 30G x 1/2 inch needle for sub-cut But anyhow sub - cut is a perfectly acceptable method of administering B12