What are the recommended hydroxocobalamin dosing regimens for acute cyanide poisoning and for vitamin B12 deficiency in adults and children?

Hydroxocobalamin Recommended Dosing

For vitamin B12 deficiency with neurological involvement, administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement occurs, then 1 mg intramuscularly every 2 months for life; for B12 deficiency without neurological involvement, give 1 mg intramuscularly three times weekly for 2 weeks, followed by maintenance of 1 mg intramuscularly every 2-3 months lifelong. 1

For acute cyanide poisoning in adults, administer 5 g intravenously (increasing to 10 g for cardiac arrest), and for children, give 70 mg/kg intravenously with a maximum dose of 5 g. 1, 2

Vitamin B12 Deficiency Dosing

With Neurological Involvement

• Administer hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further clinical improvement 1
• After initial intensive treatment, transition to maintenance therapy with 1 mg intramuscularly every 2 months for life 1
• Seek urgent specialist advice from neurology and hematology when neurological symptoms are present (unexplained sensory/motor symptoms, gait disturbances) 1

Without Neurological Involvement

• Administer hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks 1, 3
• Follow with maintenance treatment of 1 mg intramuscularly every 2-3 months for life 1, 3

Critical Caveat

• Never administer folic acid before treating B12 deficiency, as this can mask B12 deficiency and precipitate subacute combined degeneration of the spinal cord 1

Acute Cyanide Poisoning Dosing

Adult Dosing

• Standard dose: 5 g intravenously for suspected cyanide poisoning with severe manifestations (altered mental status, shock, respiratory distress) 1, 2, 4
• Cardiac arrest dose: 10 g intravenously when the patient is in cardiac arrest from cyanide toxicity 1, 2
• Infuse the initial 5 g dose over 15 minutes 2

Pediatric Dosing

• Administer 70 mg/kg intravenously (maximum 5 g) for children with moderate to severe cyanide poisoning 1, 2, 4
• Moderate signs include: Glasgow Coma Scale score ≤13, confusion, stridor, hoarse voice, polypnea, dyspnea, soot in airways 1
• Severe signs include: Glasgow Coma Scale score ≤8, seizures, coma, mydriasis, severe hemodynamic disorders, collapse, respiratory depression 1

Clinical Indicators for Treatment

• Plasma lactate ≥8 mmol/L in pure cyanide poisoning or ≥10 mmol/L in fire victims without severe burns suggests significant cyanide toxicity warranting treatment 1, 2, 4
• Smoke inhalation with cardiovascular collapse, shock, or coma 2, 4
• Cardiac or respiratory arrest in fire victims 2, 4
• Depressed mental status, seizures, or neurological deterioration 2

Adjunctive Therapy

• Add sodium thiosulfate 12.5 g intravenously for adults (250 mg/kg for children) following hydroxocobalamin to enhance cyanide elimination 2
• Administer 100% oxygen concurrently to accelerate carboxyhemoglobin elimination and counteract cyanide's mitochondrial effects 2, 4

Important Safety Considerations

• Do not delay treatment for laboratory confirmation; clinical suspicion warrants empiric administration 2, 4
• Hydroxocobalamin can cause oxalate nephropathy; monitor renal function 2
• Expected side effects include chromaturia and erythroderma, which are benign 5, 6
• The American Heart Association recommends hydroxocobalamin as the primary antidote because it does not cause hypotension or impair oxygen-carrying capacity, unlike methemoglobin-forming agents 2, 4

Common Pitfall

• Significant delays in hydroxocobalamin administration are associated with worse outcomes; median time to administration in one study was 208 minutes, with longer delays in patients who died 7
• The package insert states hydroxocobalamin should be given "without delay" when cyanide poisoning is suspected 7