Initial treatment of vitamin B12 deficiency anaemia in adults typically involves intramuscular injections of hydroxocobalamin 1 mg, administered three times a week for 2 weeks, especially in cases of suspected or confirmed deficiency caused by malabsorption or autoimmune gastritis NICE NG239.
Following initial correction, lifelong intramuscular vitamin B12 replacement is recommended for those with autoimmune gastritis, total gastrectomy, or terminal ileal resection, with a typical dose of 1 mg intramuscularly every 2–3 months for life NICE NG239.
Alternatively, high-dose oral vitamin B12 (at least 1 mg daily) can be considered for maintenance therapy, especially in cases not related to malabsorption, with clinical judgement exercised based on individual circumstances NICE CKS,NICE CKS,NICE CKS.
The duration of initial therapy is generally around 2 weeks for parenteral treatment, with ongoing maintenance depending on the underlying cause and response, often lifelong in cases of malabsorption or autoimmune conditions NICE NG239.