Sodium Nitrite

How it works

It oxidises haemoglobin to methaemoglobin, which preferentially binds free cyanide as cyanmethaemoglobin, drawing cyanide away from cytochrome oxidase and restoring cellular aerobic respiration.

Prescribing in practice

• It deliberately induces methaemoglobinaemia, so it can cause dangerous hypoxia and hypotension and must be given cautiously, particularly where smoke inhalation may coexist with carbon monoxide poisoning.
• Administer by slow intravenous injection with close haemodynamic monitoring because of its vasodilator and hypotensive effects.
• Treatment of serious cyanide poisoning should follow specialist toxicology or poisons-centre advice, and an alternative antidote may be preferred in some situations.

Monitoring

Monitor blood pressure continuously and check methaemoglobin levels to avoid excessive methaemoglobinaemia during and after treatment.

Counselling the patient

• Explain to the team that this antidote works by creating a controlled level of methaemoglobin to trap cyanide.
• Highlight the need to watch closely for a fall in blood pressure during administration.
• Note that it is typically used alongside a second agent such as sodium thiosulfate.

Evidence & guidelines

Sodium nitrite combined with sodium thiosulfate is a long-established regimen for acute cyanide poisoning, with use guided by UK poisons information (TOXBASE) advice.