Sodium Nitrate is an Antidote for Cyanide Poisoning
Among the options listed, sodium nitrate is the correct antidote for cyanide poisoning. The 2025 American Heart Association guidelines explicitly recommend sodium nitrite (the active form) as a Class 1 recommendation when hydroxocobalamin is unavailable 1.
Mechanism and Clinical Use
Sodium nitrite works by oxidizing hemoglobin to methemoglobin, which then binds cyanide to form cyanmethemoglobin, effectively sequestering the toxin away from mitochondrial cytochrome oxidase 1. This allows cellular respiration to resume.
The preferred first-line antidote is hydroxocobalamin (vitamin B12a), which directly scavenges cyanide on an equimolar basis to form nontoxic cyanocobalamin 1. However, when hydroxocobalamin is unavailable, sodium nitrite serves as an appropriate alternative with Class 1 evidence supporting its use 2.
Treatment Algorithm
- First choice: Hydroxocobalamin 5g IV for adults (70 mg/kg for children) 2
- Alternative when hydroxocobalamin unavailable: Sodium nitrite 300 mg IV for adults (6 mg/kg for children) 2
- Adjunctive therapy: Sodium thiosulfate 12.5g IV for adults (250 mg/kg for children) can be added to either agent 2
- Supportive care: 100% oxygen should be administered regardless of oxygen saturation 2
Critical Dosing Considerations
Sodium nitrite dosing must be precise in children and anemic patients to avoid excessive methemoglobin formation 2. The prescribing information contains specific weight-based and hemoglobin-adjusted dosing tables that must be consulted.
Important caveat: Sodium nitrite can worsen cellular hypoxia in patients with concomitant carbon monoxide poisoning (common in structure fires) because it reduces oxygen-carrying capacity 1. This is why hydroxocobalamin is strongly preferred in smoke inhalation victims 2.
Why the Other Options Are Incorrect
Atropine: While atropine has been studied in animal models and may enhance sodium nitrite absorption by reversing cyanide-induced bradycardia 3, 4, it is not itself a cyanide antidote. It treats muscarinic effects in organophosphate poisoning, not cyanide toxicity.
Ammonia: Has no role in cyanide poisoning treatment and is not mentioned in any guidelines.
Viagra (sildenafil): A PDE5 inhibitor used for erectile dysfunction and pulmonary hypertension 5. It has no antidotal properties for cyanide and is actually contraindicated with nitrates due to severe hypotension risk 5.
Ortho-oxyhemoglobin: This is not a recognized antidote or therapeutic agent for cyanide poisoning.
Clinical Recognition
Cyanide poisoning presents with rapid cardiovascular collapse, severe metabolic acidosis with elevated lactate, altered mental status, seizures, and potential cardiac arrest 2, 1. Diagnosis is clinical—confirmatory testing is not rapidly available 1. High suspicion is warranted in structure fire victims, industrial exposures (jewelry cleaning, electroplating), and ingestions of cyanogenic compounds 2, 1.
The mortality rate remains high even with appropriate antidote administration, particularly in patients already in cardiac arrest (87% mortality in one series) 1, emphasizing the importance of early recognition and immediate treatment.