Pharmacology · Specific antidotes
Sodium nitrite !
A cyanide antidote that turns some haemoglobin into methaemoglobin, which pulls cyanide off mitochondria. It is followed by sodium thiosulfate.
Updated 2026-11-01
Mechanism of action
Cyanide binds cytochrome a₃ of cytochrome c oxidase and stops cells using oxygen, causing lactic acidosis and rapid collapse. Sodium nitrite oxidises part of the haemoglobin to methaemoglobin, which binds cyanide more strongly than cytochrome oxidase does, forming non-toxic cyanomethaemoglobin; aerobic respiration can resume. Vasodilation may add to the effect. Sodium thiosulfate is then given to convert the cyanide to thiocyanate.
- Cyanide blocks cytochrome c oxidase
- Nitrite turns some haemoglobin into methaemoglobin
- Methaemoglobin captures cyanide: cyanomethaemoglobin
- Mitochondria use oxygen again; thiosulfate follows
Pharmacokinetics
- Elimination
- Mainly by the kidneys; adverse effects increase in kidney impairment
Indications
- Serious or life-threatening acute cyanide poisoning, in sequence with sodium thiosulfate (not available in Colombia at the time of the national guide) Cyanide poisoning →
Adverse effects
Common
- Headache, dizziness and blurred vision
- Nausea and vomiting
- Tachycardia, palpitations and syncope
- Cyanosis from methaemoglobin
Contraindications
- No absolute contraindications; other options are preferred when oxygen reserve is low: smoke inhalation (carbon monoxide), anaemia, heart or lung disease
- Congenital methaemoglobin reductase deficiency and G6PD deficiency (higher risk)
- Uncertain diagnosis of cyanide poisoning in a patient who is not in extremis
Key interactions
- Other drugs that lower blood pressure
- Additive hypotension
What is monitored
- Blood pressure, continuously
- Methaemoglobin and oxyhaemoglobin by co-oximetry
- Lactate and acid-base status
Administration and safety
- Slow intravenous injection over several minutes
- Sodium thiosulfate is given immediately afterwards
- Airway, oxygen and circulatory support are never delayed to give it
- Children receive reduced, weight-based amounts
Nursing care
- Give oxygen and protect staff from contaminated clothing or gas
- Measure blood pressure frequently during and after the injection
- Expect cyanosis from methaemoglobin; pulse oximetry is unreliable
- In fire victims, suspect carbon monoxide as well as cyanide
Pregnancy and breastfeeding
Cyanide poisoning is a medical emergency for mother and fetus, so life-saving treatment is not withheld in pregnancy.
Test yourself
Think of the answer, then tap the question to see it.
How does sodium nitrite counter cyanide?
It forms methaemoglobin, which binds cyanide as cyanomethaemoglobin and frees cytochrome oxidase.
Why is sodium nitrite risky in smoke inhalation victims?
Carbon monoxide already reduces oxygen carriage; adding methaemoglobin can worsen hypoxia.
What is the main adverse effect to monitor during the injection?
Hypotension, along with excessive methaemoglobinaemia.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - SODIUM NITRITE injection, solution (DailyMed (U.S. National Library of Medicine), 2026); Guía para el Manejo de Emergencias Toxicológicas (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); eEML - Electronic Essential Medicines List (World Health Organization, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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