Hydroxocobalamin 💊
Related Subjects:
|Hydroxocobalamin - Cyanocobalamin (B12)
|Anaemia: Assessment
💊 Hydroxocobalamin is the injectable vitamin B12 used in the UK for pernicious anaemia and other B12 deficiency. A high-dose IV formulation (Cyanokit) is the antidote of choice for cyanide poisoning. Oral B12 in the UK is cyanocobalamin; oral hydroxocobalamin is not available.
📖 About
- Preferred to cyanocobalamin for injection because it is retained longer in the body, so maintenance doses are needed only every 2–3 months.
- Always check the BNF for full prescribing information.
⚙️ Mode of Action
- Converted to the active coenzymes methylcobalamin (methionine synthase → DNA synthesis, folate recycling) and adenosylcobalamin (methylmalonyl-CoA mutase → myelin integrity).
- Cyanide antidote: the cobalt ion binds cyanide to form cyanocobalamin, which is excreted in urine.
🎯 Indications
- Pernicious anaemia and other B12 deficiency due to malabsorption (gastrectomy, ileal disease or resection).
- B12 deficiency with neurological involvement (subacute combined degeneration).
- Tobacco amblyopia and Leber's optic atrophy.
- Cyanide poisoning (Cyanokit) - e.g. smoke inhalation with lactate >8–10 mmol/L, coma, or cardiovascular instability.
💊 Dose (adult, IM)
| Indication | Loading | Maintenance |
|---|
| Pernicious anaemia/B12 deficiency, no neurological involvement | 1 mg three times a week for 2 weeks | 1 mg every 3 months |
| B12 deficiency with neurological involvement | 1 mg on alternate days until no further improvement | 1 mg every 2 months |
| Prophylaxis (e.g. after total gastrectomy) | - | 1 mg every 2–3 months |
| Cyanide poisoning (Cyanokit) | 5 g IV over 15 minutes | Second 5 g over 15 minutes–2 hours if needed (max total 10 g) |
🧪 Monitoring
- Check reticulocyte response (peaks around day 5–7) and FBC at about 10 days, then periodically.
- Potassium in the first days of treatment for severe megaloblastic anaemia (hypokalaemia during rapid haemopoiesis).
- Check folate - treat folate deficiency only after B12 has been started (folic acid alone may precipitate subacute combined degeneration).
- Anti-intrinsic factor antibodies support the diagnosis of pernicious anaemia; consider coeliac disease and malabsorption.
🔄 Interactions
- Chloramphenicol may blunt the haematological response.
- Cyanokit is incompatible with many drugs in the same line (e.g. diazepam, dobutamine, sodium thiosulfate) - use a separate line.
⚠️ Cautions
- Do not give B12 before the diagnosis is confirmed unless there is neurological urgency (it masks the diagnosis) - take bloods first.
- Cyanokit: turns skin and urine red for days to weeks and interferes with colorimetric lab tests (creatinine, bilirubin, LFTs, haemoglobin) and haemodialysis alarms - take bloods before giving; may raise BP.
🚫 Contraindications
💥 Side Effects
- IM: injection-site pain, itch, rash, nausea, headache, dizziness; rarely anaphylaxis.
- Hypokalaemia early in treatment of severe anaemia.
- Cyanokit: red skin/urine, hypertension, rash, allergic reactions.
📚 References
