What’s in a name?
- Vitamin B12:
- Refers to a specific group of cobalt-containing corrinoids, also referred to as cobalamins.
- Terms cobalamin and vitamin B12 are generally used interchangeably.
- Adenosylcobalamin – active coenzyme form
- Methylcobalamin – active coenzyme form
- Hydroxocobalamin – Food cobalamin; also a synthetic form of vitamin B12.
- Cyanocobalamin – stable synthetic pharmaceutical that has to be converted to adenosylcobalamin or methylcobalamin to become metabolically active.
What are the possible routes for delivering vitamin B12?
|Parenteral vitamin B12||Avoids potential problems with compliance or absorption.||Requires visit to medical office.||Generally preferred for initial therapy in patients with significant neurologic symptoms.|
|Oral vitamin B12||May be as effective as parenteral vitamin B12 in patients with normal absorption; less painful and usually lower cost than injection.||May not be appropriate if absorption or compliance problematic.||High-dose tablets of 1,000 mcg expected to deliver about 5-40 mcg of vitamin B12 assuming oral dose absorption rate of 0.5%-4%.|
|Intranasal vitamin B12||Easy to use.||N/A||Initial dose: 1 spray (500 mcg) in 1 nostril once weekly;|
administer ≥ 1 hour before or ≥ 1 hour after ingestion of hot foods or liquids.
Treatment protocols for patients without neurological involvement vary. Some examples include:
- Initial therapy with vitamin B12:
- 1,000 mcg intramuscularly 3 times weekly for 2 weeks
- 1,000 mcg/day orally
- 1,000 mcg intramuscularly per day or every other day for 1 week, followed by weekly injections up to 8 weeks, followed by every 3-4 weeks
- Maintenance therapy with vitamin B12:
- For irreversible cases (such as pernicious anemia, or after gastric surgery), continue treatment for life typically with vitamin B12 1,000-2,000 mcg/day orally or monthly parenteral cyanocobalamin 1,000 mcg (or hydroxocobalamin 1,000 mcg every 3 months).
Which of the following are potential risks of vitamin B12 replacement?
Expected response to therapy:
- Neurologic improvement within 1 week
- Normalization of mean cell volume within 8 weeks
This patient was treated with vitamin B12 1,000 mcg intramuscularly 3 times weekly for 2 weeks followed by monthly injections of 1,000 mcg. As shown below, his complete blood count showed rapid improvement: