Metformin (for longer than 12 months)
- No need to routinely check B12 levels for those with diabetes on metformin but consider checking if potentially symptomatic or other risk factors for deficiency e.g. PPI or colchicine treatment, vegetarian / vegan diet, previous low B12 levels and / or conditions associated with malabsorption e.g. post gastrectomy surgery, inflammatory bowel disease (MHRA guidance June 2022).
- Usually improves with dietary improvement of B12 intake
- It has been suggested that an increased intake of calcium reverses the vitamin B12 malabsorption induced by metformin. Bauman WA et al, Diabetes Care 2000 (23) 1227-31
- Only assess B12 levels if objective evidence of deficiency is present including peripheral neuropathy or macrocytic anaemia. A FBC is included in the annual diabetes GP Order Comms (ICE) test request set, giving an additional safety net
- If low levels check IFAB and should be treated with a short course of OTC oral cyanocobalamin (50micrograms orally for 4 weeks). Response should be assessed clinically and continued if benefit is shown
- No need for prophylactic B12 administration.
Proton pump inhibitors and H2 antagonists
- OTC oral replacement (25-100 micrograms orally) may be appropriate if objective evidence of deficiency is found
Anticonvulsants
- If no objective features of B12 deficiency – no need for replacement
- OTC oral replacement (25-100 micrograms orally) may be appropriate if objective evidence of deficiency is found
Oral contraceptives and hormone replacement therapy
- Pregnancy and COCP cause altered B12 binding to plasma protein, so borderline / low levels are commonly seen, which may not indicate true deficiency
- Only assess B12 levels if objective symptoms develop and this is the only indication for treatment
- OTC oral replacement (25-100 micrograms orally) may be appropriate if objective evidence of deficiency is found
Colchicine
- Low levels can easily be increased with dietary supplementation
Antibiotics
- Low levels can easily be increased with dietary supplementation
Pregnancy
- Pregnancy and COCP cause altered B12 binding to plasma protein, so borderline/low levels are commonly seen, which may not indicate true deficiency
- B12 is not routinely measured during pregnancy, therefore only test if symptoms develop (as per protocol above for non-pregnant patients)
- If pregnant or breastfeeding it is recommended that cyanocobalamin is prescribed rather than over-the-counter
Vegetarian and vegan diets
- Vegetarians and vegans are at increased risk of B12 deficiency, especially during pregnancy and when breastfeeding. If relevant symptoms develop consider testing B12 levels, and oral supplementation may be required as per above protocol. If felt appropriate oral supplementation could be over the counter (NB: please provide the patient with instructions for what dose of cyanocobalamin to take as OTC supplements vary widely). However, if pregnant or breastfeeding it is recommended that cyanocobalamin is prescribed.
- Please see the Vegan Society advice.
C.M & A.K. 01-08-25
