Cyanocobalamin

How it works

It is converted in the body to the active coenzymes methylcobalamin and adenosylcobalamin, which are required for DNA synthesis and normal red cell and neuronal function.

Prescribing in practice

• In deficiency with neurological involvement or pernicious anaemia, parenteral hydroxocobalamin is generally preferred, as oral cyanocobalamin relies on adequate absorption.
• Identify and address the underlying cause of deficiency rather than treating the blood result alone.
• Correcting B12 deficiency can unmask or precipitate hypokalaemia as haematopoiesis recovers.

Monitoring

Monitor the haematological response and serum potassium during initial correction of significant deficiency.

Counselling the patient

• Lifelong treatment may be needed if the cause of deficiency is permanent, such as pernicious anaemia.
• Tell your team if you follow a vegan diet or have had gastrointestinal surgery, as these affect B12.
• Take oral preparations as directed and report return of symptoms such as fatigue or tingling.

Evidence & guidelines

Use of vitamin B12 replacement in deficiency is long-established standard practice; consult current prescribing references on choice of preparation and route.