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Antidotes & Toxicology Pregnancy: Use if benefit outweighs risk — cyanide poisoning is lethal; hydroxocobalamin preferred in pregnancy

Sodium Nitrite

Brand names: Sodium Nitrite Injection

Adult dose

Dose: 300 mg (10 mL of 3% solution)
Route: IV
Frequency: Single dose
Max: 300 mg
Infuse over 5–20 minutes. Always follow immediately with sodium thiosulfate 12.5 g IV. Repeat at half dose if symptoms persist

Paediatric dose

Dose: 6 mg/kg (0.2 mL/kg of 3% solution) mg/kg
Route: IV
Frequency: Single dose
Max: 300 mg
Seek specialist opinion; always follow with sodium thiosulfate; adjust dose based on haemoglobin if available

Dose adjustments

Renal

No dose adjustment; monitor for thiocyanate accumulation from thiosulfate component

Hepatic

No specific adjustment

Paediatric weight-based calculator

Seek specialist opinion; always follow with sodium thiosulfate; adjust dose based on haemoglobin if available

Clinical pearls

  • Mechanism: nitrite oxidises haemoglobin to methaemoglobin, which has higher affinity for cyanide than cytochrome oxidase — cyanmethaemoglobin complex diverts cyanide away from mitochondria
  • ALWAYS follow with sodium thiosulfate — thiosulfate provides sulfur donor for rhodanese enzyme, converting cyanide to thiocyanate (renally excreted); together they form a two-step antidote kit
  • PREFER hydroxocobalamin (Cyanokit) in most ED scenarios — does not cause methaemoglobinaemia, compatible with CO poisoning, safer for smoke inhalation victims; sodium nitrite/thiosulfate is an alternative when hydroxocobalamin is unavailable
  • MHRA: licensed in UK as cyanide antidote; always consult NPIS (0344 892 0111) before use — cyanide poisoning is rare
  • Methaemoglobin target: 20–30% — measured by co-oximetry (standard SpO2 is unreliable)
  • Sources of cyanide poisoning: smoke inhalation (HCN from burning plastics), industrial exposure (electroplating, chemical plants), sodium nitroprusside infusion toxicity, apricot kernel/bitter almond ingestion

Contraindications

  • Concurrent carbon monoxide poisoning (methaemoglobinaemia + carboxyhaemoglobinaemia = fatal hypoxia)
  • Smoke inhalation without confirmed cyanide exposure — use hydroxocobalamin instead
  • G6PD deficiency (relative — risk of haemolysis)

Side effects

  • Hypotension (vasodilation — major risk; have IV fluids ready)
  • Methaemoglobinaemia (therapeutic mechanism but overdose is dangerous)
  • Tachycardia
  • Headache and flushing
  • Nausea
  • Methaemoglobin level above 30% is dangerous

Interactions

  • Hydroxocobalamin (do NOT co-administer — both bind cyanide; give sequentially if needed)
  • Carbon monoxide (fatal synergy with methaemoglobinaemia)

Monitoring

  • Blood pressure (hypotension risk during infusion)
  • Methaemoglobin levels via co-oximetry
  • Lactate (cyanide toxicity marker)
  • Blood cyanide concentration if available
  • Clinical response (consciousness, haemodynamics)

Reference: BNFc; BNF 90; NPIS Toxbase; Poisoning Emergency Book; WHO Model Formulary. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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