Cyanide Antidote (Vitamin B12 Precursor at High Dose) Pregnancy: Animal studies showed teratogenic effects; no adequate human data. Given no more than two injections, the potentially life-threatening indication and lack of alternative, hydroxocobalamin may be given to a pregnant woman. Discontinue breast-feeding after treatment.

Hydroxocobalamin (High-Dose — Cyanide Antidote)

Brand names: Cyanokit 5 g

Used in: Anaemia

High-dose hydroxocobalamin is a form of vitamin B12 used in the critical care and emergency setting as an antidote for known or suspected cyanide poisoning, including smoke-inhalation injury.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 5 g (initial dose, 2 x 100 mL)

Route: Intravenous infusion

Frequency: Initial dose over 15 minutes; depending on severity and clinical response a second 5 g dose may be given (infusion rate for the second dose ranges from 15 minutes for extremely unstable patients up to 2 hours)

Max: Maximum total recommended dose 10 g

Cyanide antidote (Cyanokit). Treatment decisions are made on clinical history/signs of cyanide intoxication. Does not substitute oxygen therapy and must not delay airway, oxygenation, hydration, cardiovascular support and seizure management.

Paediatric dose

Dose: 70 mg/kg

Route: Intravenous infusion

Frequency: Initial dose over 15 minutes; a subsequent dose of 70 mg/kg may be given depending on severity and response

Max: Each dose not exceeding 5 g; maximum total recommended dose 140 mg/kg not exceeding 10 g

Infants to adolescents (0 to 18 years old). Example initial doses: 0.35 g (5 kg), 0.70 g (10 kg), 1.40 g (20 kg), 2.10 g (30 kg), 2.80 g (40 kg), 3.50 g (50 kg), 4.20 g (60 kg).

Dose adjustments

Renal

No dose adjustment required in renal or hepatic impairment (administered as emergency therapy in an acute, life-threatening situation).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Infants to adolescents (0 to 18 years old). Example initial doses: 0.35 g (5 kg), 0.70 g (10 kg), 1.40 g (20 kg), 2.10 g (30 kg), 2.80 g (40 kg), 3.50 g (50 kg), 4.20 g (60 kg).

Verify in a children's formulary

Contraindications

None stated in the UK SPC (§4.3). US labelling additionally lists known hypersensitivity to hydroxocobalamin, vitamin B12 preparations, cobalt or benzyl alcohol, and administration to patients with hereditary optic nerve atrophy (Leber's disease).

Side effects

Reversible red colouration of the skin and mucous membranes (up to about 15 days)
Chromaturia — dark red colouration of the urine (may last up to 35 days)
Allergic reactions including angioneurotic oedema, urticaria and pruritus
Transient increase in blood pressure; hot flush
Acute renal failure with acute tubular necrosis and urine calcium oxalate crystals; headache, injection site reaction, GI upset

Clinical monograph

How it works

It binds cyanide ions to form cyanocobalamin, which is non-toxic and renally excreted, thereby removing cyanide from cytochrome oxidase and restoring cellular aerobic respiration.

Prescribing in practice

Give promptly in suspected cyanide poisoning without waiting for confirmatory levels, as treatment is time-critical and the antidote has a relatively favourable safety profile.
It characteristically causes a deep red discoloration of the skin, mucous membranes and urine, and can interfere with several colorimetric laboratory assays.
Hypertension and hypersensitivity reactions can occur; reconstitute and administer according to the SPC.

Monitoring

Monitor blood pressure, oxygenation and clinical response, and interpret affected laboratory results with awareness of the red discoloration interference.

Counselling the patient

Team: reddish discoloration of skin and urine is expected and can persist for days.
Team: some laboratory colorimetric tests may be unreliable after administration.

Evidence & guidelines

High-dose hydroxocobalamin is an established first-line cyanide antidote used in smoke-inhalation and other cyanide-exposure scenarios.

Reference: MHRA SPC Cyanokit; TOXBASE NPIS; UK National Poisons Information Service; Borron et al. Ann Emerg Med 2007 (Cyanokit efficacy); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators