sodium nitrite + sodium thiosulfate: clinical use

Prescribing considerations

• Reserve for acute cyanide poisoning judged life-threatening; if the diagnosis is uncertain, weigh the antidote's potentially life-threatening toxicity against likely benefit.
• Do not delay airway management, oxygenation, decontamination, cardiovascular support or seizure control.
• Use particular caution with smoke inhalation, possible carbon monoxide poisoning, anaemia, blood loss, or impaired cardiac or respiratory reserve.
• Consider alternative approaches in known or suspected G6PD deficiency because sodium nitrite may precipitate haemolysis.
• Account for the sodium, potassium, boric acid and possible trace sulfite content of the thiosulfate component.
• Prevent selection errors: NHS England has highlighted fatal risk from unintended sodium nitrite administration.

Contraindications and cautions

• Hypersensitivity to sodium nitrite, sodium thiosulfate or an excipient.

Monitoring

• Continuous clinical assessment of airway, ventilation, oxygenation and circulation
• Blood pressure during administration and afterwards
• Methaemoglobin concentration and clinical evidence of impaired oxygen delivery
• Haemoglobin and oxygen-carrying reserve, particularly with anaemia or blood loss
• Haematocrit and evidence of haemolysis when G6PD deficiency is known or suspected
• Neurological status, cardiac rhythm and recurrence or progression of cyanide-toxicity features

Clinical pharmacology

Sodium nitrite oxidises haemoglobin to methaemoglobin, which preferentially binds cyanide and helps restore cytochrome oxidase activity. Sodium thiosulfate acts as a sulfur donor for enzymatic conversion of cyanide to relatively non-toxic thiocyanate; some thiosulfate is eliminated unchanged by the kidneys.

Formulation and product differences

• The co-pack contains separate sodium nitrite 30 mg/mL and sodium thiosulfate 250 mg/mL solutions for injection.
• Both are clear, colourless, single-use vial presentations.
• The thiosulfate solution contains potassium chloride and boric acid and may contain trace sodium sulfite.
• Hydroxocobalamin must not be administered simultaneously through the same intravenous line.