In the case of injections, up to 70% of the active substance can be absorbed by the body
If the result is higher than 100, the injection will not fit in a one-milliliter syringe
Injections are favored for severe deficiency, malabsorption (e.g., postGI surgery, chronic diarrhea), very low B12 levels with neurologic signs, poor adherence, or when rapid repletion is needed
Common adverse effects include: Injection site reactions pain, redness, swelling, or bruising at the intramuscular injection site Gastrointestinal disturbances nausea, diarrhoea, or abdominal discomfort Headache and dizziness particularly following initial doses Skin reactions including rash, pruritus, or acne-like eruptions Flushing temporary redness of the skin Chromaturia red-coloured urine (harmless but can cause concern if unexpected) Less common but more serious reactions include: Hypersensitivity reactions ranging from mild urticaria to anaphylaxis (rare but potentially life-threatening) Hypokalaemia particularly during initial treatment when rapid cell production occurs [5] [16] Temporary changes in blood counts during correction of deficiency Interference with laboratory tests primarily with high-dose IV hydroxocobalamin used for cyanide poisoning, not typically with standard 1mg IM replacement doses Cautions and contraindications: Hypersensitivity to cobalt or vitamin B12 Cyanocobalamin should be avoided in Leber's hereditary optic neuropathy [2] [17] Chloramphenicol may reduce the haematological response to B12 therapy Patients receiving B12 injections outside clinical necessity face unnecessary risks without proven benefit
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