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Cyanide antidote Pregnancy: Animal studies showed teratogenic effects following daily exposure throughout organogenesis; there are no adequate data in pregnant women. Given that no more than two injections are administered, the condition is potentially life-threatening and there is no alternative treatment, hydroxocobalamin may be given to a pregnant woman. Breast-feeding is not a contraindication, but discontinuation of breast-feeding is recommended after treatment (§4.6).

Hydroxocobalamin (Cyanokit)

Brand names: Cyanokit

Used in: Anaemia

Hydroxocobalamin (Cyanokit formulation) is a form of vitamin B12 used at high dose as an antidote for known or suspected cyanide poisoning, including smoke inhalation; lower-dose hydroxocobalamin is also used to treat vitamin B12 deficiency.

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 (2 × 100 mL)
Route: Intravenous infusion over 15 minutes
Frequency: Single initial dose; depending on the severity of the poisoning and the clinical response a second dose of 5 g may be administered
Max: Maximum total recommended dose 10 g
eMC §4.2 (Cyanokit 5 g powder for solution for infusion, for known or suspected cyanide poisoning). The initial dose is administered as an intravenous infusion over 15 minutes; the rate of intravenous infusion for the second dose ranges from 15 minutes (for extremely unstable patients) to 2 hours based on patient condition. Treatment must include immediate attention to airway patency, adequacy of oxygenation and hydration, cardiovascular support and management of seizures; Cyanokit does not substitute for oxygen therapy. Causes a reversible red colouration of skin and mucous membranes (up to 15 days) and dark red chromaturia (up to 35 days), and red discolouration of plasma may interfere with laboratory measurements.

Paediatric dose

Dose: 70 mg/kg
Route: Intravenous infusion over 15 minutes
Frequency: Single initial dose; a subsequent dose of 70 mg/kg may be administered depending on the severity of the poisoning and the clinical response
Max: Each dose not exceeding 5 g; maximum total recommended dose 140 mg/kg not exceeding 10 g
eMC §4.2 — stated for infants to adolescents (0 to 18 years old). SPC worked examples: 5 kg = 0.35 g (14 mL), 10 kg = 0.70 g (28 mL), 20 kg = 1.40 g (56 mL), 30 kg = 2.10 g (84 mL), 40 kg = 2.80 g (112 mL), 50 kg = 3.50 g (140 mL), 60 kg = 4.20 g (168 mL). Limited data in children 0–18 years showed no difference in safety profile versus adults. Verify against a children's formulary before administration.

Dose adjustments

Renal

Although safety and efficacy have not been studied in renal or hepatic impairment, Cyanokit is administered as emergency therapy in an acute, life-threatening situation only and no dose adjustment is required in these patients (§4.2).

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

eMC §4.2 — stated for infants to adolescents (0 to 18 years old). SPC worked examples: 5 kg = 0.35 g (14 mL), 10 kg = 0.70 g (28 mL), 20 kg = 1.40 g (56 mL), 30 kg = 2.10 g (84 mL), 40 kg = 2.80 g (112 mL), 50 kg = 3.50 g (140 mL), 60 kg = 4.20 g (168 mL). Limited data in children 0–18 years showed no difference in safety profile versus adults. Verify against a children's formulary before administration.

Verify in a children's formulary

Contraindications

  • None (SPC §4.3 states "None")
  • Note: known hypersensitivity to hydroxocobalamin or vitamin B12 must be taken into benefit-risk consideration before administration (§4.4)

Side effects

  • Reversible red colouration of the skin and mucous membranes (most patients, up to 15 days) and chromaturia — dark red urine, up to 35 days
  • Allergic reactions including angioneurotic oedema, skin eruption, urticaria and pruritus
  • Transient increase in blood pressure (usually resolving within several hours); hot flush
  • Acute renal failure with acute tubular necrosis, renal impairment, urine calcium oxalate crystals
  • Headache, dizziness, nausea, vomiting, abdominal discomfort; injection site reaction; pustular rashes affecting mainly the face and neck

Clinical monograph

How it works

Hydroxocobalamin binds cyanide to form cyanocobalamin, a stable, relatively non-toxic compound that is renally excreted, thereby releasing cytochrome oxidase and restoring aerobic metabolism.

Prescribing in practice

  • In suspected cyanide toxicity it should be given without delay as a time-critical antidote alongside supportive care, and is given by the intravenous route in the emergency setting.
  • Causes a characteristic deep red discolouration of skin, urine, and serum that can interfere with co-oximetry and several laboratory colorimetric assays for a period after administration.
  • Hypersensitivity reactions and transient rises in blood pressure may occur; refer to the SPC for the antidote product.

Monitoring

Monitor blood pressure, clinical response, oxygenation, and be aware that red discolouration can confound certain laboratory and oximetry results.

Counselling the patient

  • Your skin and urine may turn red for a few days after the antidote, which is expected and harmless.
  • Tell laboratory staff you have received this medicine as it can affect some blood test readings.

Evidence & guidelines

Hydroxocobalamin is an established antidote for cyanide poisoning and smoke-inhalation-associated cyanide toxicity, supported by toxicology guidance and resuscitation and poisons information sources.

Reference: TOXBASE; NPIS; Cyanokit SPC; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

Pathways
📚 MRCEM Revision

Featured in these MRCEM clinical pathways

Hydroxocobalamin (Cyanokit) is a core drug in the following exam-focused workups on our sister siteReviseMRCEM.

MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.