Cyanide Antidote (Vitamin B12 Precursor at High Dose) Pregnancy: Use if life-threatening cyanide poisoning — maternal and fetal benefit outweighs theoretical risk of high-dose vitamin B12 exposure

Hydroxocobalamin (High-Dose — Cyanide Antidote)

Brand names: Cyanokit 5 g

Adult dose

Dose: Initial: 5 g IV over 15 minutes; second dose 5 g over 15-120 minutes if inadequate response; third dose 5 g if life-threatening — maximum 15 g total

Route: Intravenous infusion

Frequency: Single 5 g dose; repeat if needed (up to 3 doses)

Max: 15 g total

Smoke inhalation with suspected cyanide poisoning; confirmed cyanide poisoning; given empirically in fire casualties with altered consciousness — does not require confirmed diagnosis; compatible with other resuscitation measures

Paediatric dose

Dose: 70 mg/kg IV over 15 minutes; repeat if needed mg/kg

Route: Intravenous

Frequency: Single dose, repeat if inadequate response

Max: 10.5 g total (3 × 70 mg/kg)

Paediatric fire casualties with altered consciousness — same empirical use principle as adults

Dose adjustments

Renal

No dose adjustment required

Hepatic

No dose adjustment required

Paediatric weight-based calculator

Patient weight (kg)

Paediatric fire casualties with altered consciousness — same empirical use principle as adults

Clinical pearls

Mechanism at high dose (5 g): each hydroxocobalamin molecule binds one cyanide ion to form cyanocobalamin (non-toxic) — at therapeutic doses, overwhelms cyanide via 1:1 molar stoichiometry; rapid onset within minutes; particularly effective in smoke inhalation victims where CO and HCN co-poisoning is common
MHRA guidance: Cyanokit is first-line cyanide antidote — superseded older agents (dicobalt edetate, which causes severe cobalt toxicity if given without cyanide poisoning); hydroxocobalamin is safe to give empirically without confirmed diagnosis — no cobalt toxicity risk
Laboratory interference: hydroxocobalamin's red colour interferes with colourimetric laboratory tests for hours — co-oximetry (SpCO), bilirubin, creatinine, glucose, and other tests may give false results; use clinical judgment; point-of-care lactate (electrochemical assay) is less affected
Skin/urine discolouration counselling: universal red discolouration of skin, mucous membranes, and urine alarming to patients and staff — brief patient/family explanation prevents unnecessary concern; clears over 24-48h; does not require any intervention
Combined CO + CN poisoning in fires: both toxins impair cellular oxygen utilisation; treat CO with 100% O2/hyperbaric O2 and cyanide with hydroxocobalamin — combined empirical treatment in any unconscious fire victim is standard practice

Contraindications

Allergy to hydroxocobalamin or cyanocobalamin (rare)

Side effects

Red/pink discolouration of skin, urine, mucous membranes (universal — lasts 2-5 days; warn patient and staff)
Hypertension (during infusion — manageable)
Nausea
Headache
Interference with clinical laboratory tests (colourimetric assays)
Photosensitivity (brief, post-infusion)

Interactions

Sodium thiosulphate — compatible and complementary cyanide antidote; do NOT co-administer through same IV line (precipitation)
Diazepam and dobutamine — chemical incompatibility — separate IV lines required

Monitoring

Arterial blood gas (lactate >10 mmol/L suggests significant CN poisoning)
Pulse oximetry (note: SpO2 unreliable post-hydroxocobalamin due to interference)
Carboxyhaemoglobin (co-oximetry — may be affected)
Blood pressure during infusion
Clinical response (consciousness, haemodynamic status)

Reference: BNFc; BNF 90; MHRA SPC Cyanokit; TOXBASE NPIS; UK National Poisons Information Service; Borron et al. Ann Emerg Med 2007 (Cyanokit efficacy). Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators