What is the recommended dose of hydroxycobalamin (Vitamin B12a) for treating cyanide toxicity?

Hydroxocobalamin Dosing for Cyanide Toxicity

For adults with suspected cyanide poisoning, administer 5 g of hydroxocobalamin IV, increasing to 10 g for cardiac arrest; for children, give 70 mg/kg IV (maximum 5 g). 1

Adult Dosing

• Standard dose: 5 g IV for suspected cyanide poisoning with severe manifestations (cardiac or respiratory arrest, shock, coma) 1
• Cardiac arrest dose: 10 g IV when the patient is in cardiac arrest from cyanide toxicity 1
• The 5 g dose effectively binds cyanide up to blood concentrations of approximately 40 μmol/L; higher concentrations require additional dosing 2
• A second 5 g dose can be administered if initial response is inadequate or if blood cyanide levels exceed 40 μmol/L 2

Administration Details for Adults

• Infuse over 15 minutes for the initial 5 g dose 1
• Maximum total dose can reach 15 g in severe cases 3
• Consider plasma lactate levels to guide treatment: lactate ≥8 mmol/L in pure cyanide poisoning or ≥10 mmol/L in fire victims without severe burns suggests significant cyanide toxicity 1, 4

Pediatric Dosing

• 70 mg/kg IV (maximum 5 g) for children with moderate to severe cyanide poisoning 1
• Administer for moderate poisoning signs: GCS ≤13, confusion, stridor, hoarse voice, polypnea, dyspnea, or soot in airways 1
• Also indicated for severe poisoning signs: GCS ≤8, seizures, coma, mydriasis, severe hemodynamic instability, collapse, or respiratory depression 1

Adjunctive Therapy

• Add sodium thiosulfate 12.5 g IV for adults (250 mg/kg for children) following hydroxocobalamin to enhance cyanide elimination 1, 5, 4
• Sodium thiosulfate acts more slowly but provides sustained detoxification; it should not be used as monotherapy in life-threatening poisoning 1, 6
• Administer 100% oxygen concurrently, as it accelerates carboxyhemoglobin elimination and counteracts cyanide's mitochondrial effects 1, 5, 4

Clinical Context and Rationale

The American Heart Association designates hydroxocobalamin as the primary recommended antidote because it does not cause hypotension or impair oxygen-carrying capacity—critical advantages when carbon monoxide co-poisoning is present in smoke inhalation victims 1. This contrasts with methemoglobin-forming agents (sodium nitrite), which reduce oxygen delivery and have shown increased mortality in animal models of combined CO/cyanide poisoning 4.

Important Caveats

• Nephrotoxicity risk: Hydroxocobalamin can cause oxalate nephropathy; monitor renal function 1
• Expected side effects: Transient red discoloration of skin, mucous membranes, and urine (chromaturia) occurs universally but is benign 7, 3
• Blood pressure effects: Hydroxocobalamin alone may cause transient hypertension (13.6% systolic, 25.9% diastolic increase) with decreased heart rate 7
• Do not delay treatment for laboratory confirmation; clinical suspicion (fire exposure, altered mental status, metabolic acidosis, elevated lactate) warrants empiric administration 1, 3

When to Suspect Severe Cyanide Poisoning

Administer hydroxocobalamin when patients present with:

• Smoke inhalation plus cardiovascular collapse, shock, or coma 1
• Cardiac or respiratory arrest in fire victims 1
• Metabolic acidosis with lactate ≥8-10 mmol/L 1, 4
• Depressed mental status, seizures, or neurological deterioration 1

The combination of hydroxocobalamin followed by sodium thiosulfate provides both immediate cyanide binding and sustained elimination, optimizing outcomes in massive poisoning cases 4, 6.