Trip Answers

Question answered:03/03/08

GP Notebook has a section on vitamin b12 deficiency [1], with regard to aetiology it reports nutritional deficiency, malabsorption, transcobalamin II deficiency and increased requirements as the 4 main causes

 

A 2005 Cochrane systematic review compared oral and intramuscular vitamin B12 [2], concluding:

 

“The evidence derived from these limited studies suggests that 2000 mcg doses of oral vitamin B12 daily and 1000 mcg doses initially daily and thereafter weekly and then monthly may be as effective as intramuscular administration in obtaining short term haematological and neurological responses in vitamin B12 deficient patients.”

 

In the full-text of the review, they report:

 

“Vitamin B12 replacement has been traditionally administered intramuscularly. However several case control and case series studies have since suggested equal efficacy and safety of the oral route (Chalmers 1958; Ross 1954; Spies 1949). The mechanism for this oral route is most probably that free vitamin B12 can be absorbed both passively (without binding to IF) as well as actively (following binding to IF) in the terminal ileum. Passive diffusion accounts for 1.2% of total absorption with a bioavailability unaffected in patients with pernicious anaemia or gastro-duodenal surgical resection (Berlin 1968; Berlin 1978). High doses of oral vitamin B12 (e.g. 1,000 micrograms daily) may be able to produce adequate absorption of vitamin B12 even in the presence of IF deficiency and therefore be an alternative to the intramuscular route in many patients.”

 

A Canadian guideline [3] reported:

 

“Oral replacement of vitamin B12 is the treatment of choice in most cases, including pernicious anemia. Patients with significant neurological symptoms, however, should receive initial intramuscular injections of 1000 ìg vitamin B12, followed by oral doses of 1000-2000 ìg/day. The duration of therapy depends on the cause of deficiency. In the case of pernicious anemia, treatment is life-long. Early treatment of vitamin B12 deficiency is particularly important because neurologic symptoms may be irreversible.”

 

In the CKS guideline on macrocytic anaemia [4] they offer the following guidance:

 

“Treatment of established vitamin B12 deficiency anaemia

 

Pernicious anaemia, or history of total gastrectomy or ileal resection
 - Initial treatment: if there has been no neurological involvement, hydroxocobalamin 1 mg intramuscularly every 2–4 days for six doses. If there has been neurological involvement, hydroxocobalamin intramuscularly 1 mg on alternate days until no further improvement.
 - Maintenance treatment: if there has been no neurological involvement, hydroxocobalamin 1 mg intramuscularly every 2–3 months for life. If there has been neurological involvement, hydroxocobalamin 1 mg every 2 months for life.

 

Poor diet (rare)
 - Initial treatment: as above.
 - Maintenance treatment is not usually necessary if diet improved. Vegans should be advised to take oral vitamin B12 supplements following acute treatment, although a twice-yearly injection is an alternative.”

 

It later reports:

 

“Oral vitamin B12 (cyanocobalamin) is included. It is suitable only for the very small minority of people with proven dietary deficiency of vitamin B12 (most vitamin B12 deficiency is due to malabsorption). It is available on an NHS prescription only for this indication, and the prescription must be endorsed 'SLS'.”

 

You may also be interested in the CKS comments on the IF and parietal cell antibodies tests:

 

“Autoantibody screen:
 - Intrinsic factor (IF) antibodies are virtually diagnostic of pernicious anaemia (PA). However, absence of IF antibodies does not exclude the diagnosis, as they are present in only 50% of people with PA (i.e. it has high specificity but low sensitivity).
 - Gastric parietal-cell antibodies are present in 85% of people with PA, but are also found in 3–10% of people who do not have PA (i.e. it has high sensitivity but low specificity).”

 

References

1) http://www.gpnotebook.co.uk/simplepage.cfm?ID=1711669255
2) http://www.cochrane.org/reviews/en/ab004655.html
3) http://www.health.gov.bc.ca/gpac/pdf/b12.pdf
4) http://cks.library.nhs.uk/anaemia_macrocytic/view_whole_guidance

 

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