Cyanocobalamin (Vitamin B12) : Anemia

Availability : Injection 1mg/ml (Pharmaniaga)
Indication & Dosages (FUKKM)

• Prophylaxis of anaemia associated with Vitamin B12 deficiency
• 250-1000 mcg IM everymonth
• Uncomplicated pernicious anaemia or Vitamin B12 malabsorption 
• Initial 100 mcg daily for 5-10 days followed by 100-200 mcg monthly until complete remission is achieved.
• Maintenance: up to 1000 mcg monthly. CHILD 30-50 mcg daily for 2 or more
  weeks (to a total dose of 1- 5mg). OR AS PRESCRIBED. 

Alternative dosing (BMJ)

• Patients with megaloblastic anaemia and pancytopenia require hospital admission
• An acute regimen of 1000 micrograms cyanocobalamin parenterally is given daily for between 1 and 2 week
• then 1000 micrograms parenterally once a week for up to 1 month, until significant reticulocytosis is seen in the marrow. 
• Folic acid supplementation may help reverse the haematological abnormalities 
• Acute and maintenance treatment of patients with mild to moderate symptoms of vitamin B12 deficiency (haematological: mild anaemia; neurological: dysaesthesia/paraesthesias, polyneuropathy, depression) is with once-daily oral cyanocobalamin or once-monthly parenteral cyanocobalamin
• In patients treated with oral cyanocobalamin, a response should be seen within 2 months. 
• If serum vitamin B12 does not rise significantly after 2 months of daily oral cyanocobalamin, clinicians should switch to intramuscular vitamin B12 or consider other causes 

Comparison with Oral route

• Parenteral therapy using the IM or SC route is by far the most reliable and most familiar treatment for vitamin B12 deficiency
• oral vitamin B12 in the form of cyanocobalamin in high doses could be absorbed even in patients with pernicious anaemia or significant terminal ileum resection
• Oral cyanocobalamin has been shown in meta-analysis to be as effective, if not more effective, in patients with vitamin B12 deficiency.
• Although absorption occurs at dosages <1000 micrograms/day, there appears to be variable absorption and less than maximal clinical and laboratory response.
• Absorption can be maximised by administering on an empty stomach

References:

1. MIMS Gateway
2. http://bestpractice.bmj.com/best-practice/monograph/822/treatment/step-by-step.html