Sodium Nitrite Overdose: Clinical Presentation and Treatment
Immediate Recognition is Critical
Sodium nitrite overdose causes life-threatening methemoglobinemia and must be treated immediately with intravenous methylene blue as the primary antidote. 1, 2
Clinical Presentation
Patients with sodium nitrite poisoning present with a characteristic constellation of findings that distinguish this from other toxidromes:
Cardinal Signs
- Cyanosis with persistent oxygen saturation around 85% despite supplemental oxygen - this is the hallmark finding that should immediately trigger suspicion 3
- Dark brown or "chocolate-colored" blood on venipuncture - a pathognomonic sign of severe methemoglobinemia 3
- Profound hypotension that develops rapidly and may be refractory to standard resuscitation 1, 3
Additional Clinical Features
- Altered mental status ranging from confusion to coma 1
- Dysrhythmias progressing to bradycardic arrest 3
- Headache, dizziness, and dyspnea in less severe cases 1
- Metabolic acidosis 1
Critical Diagnostic Pitfall
Standard pulse oximetry and calculated oxygen saturation based on PO2 are completely unreliable in methemoglobinemia - they will show falsely reassuring readings despite profound tissue hypoxia 1. Co-oximetry is required for accurate methemoglobin measurement 1.
Treatment Protocol
First-Line Antidote: Methylene Blue
Administer intravenous methylene blue immediately upon recognition - do not delay for laboratory confirmation of methemoglobin levels. 2, 4
Dosing
- Adults and children: 1-2 mg/kg IV (typically 0.1-0.2 mL/kg of 1% solution) given over 5 minutes 2
- Repeat dosing: May require higher or more frequent doses than standard methemoglobinemia protocols 2
- One survivor received treatment after ingesting 60 grams, with methemoglobin levels reaching 73% 2
Monitoring During Treatment
- Measure methemoglobin levels via co-oximetry (not standard pulse oximetry) 1
- Target methemoglobin levels below 30% 1
- Monitor blood pressure continuously - hypotension is common and severe 1, 3
- Continue monitoring for 24-48 hours as symptoms can recur 1
Alternative Antidote: Ascorbic Acid
- Used successfully when methylene blue unavailable, particularly in resource-limited settings 5
- Less rapid onset than methylene blue but effective 5
Supportive Care
Cardiovascular Support
- Aggressive IV fluid resuscitation 3
- Push-dose vasopressors (epinephrine) for refractory hypotension 3
- Prepare for rapid decompensation to cardiac arrest 3
Airway Management
- Early intubation for altered mental status or respiratory compromise 3
- Provide 100% oxygen despite unreliable pulse oximetry readings 1
Blood Products
- Packed red blood cells for severe cases 3
- Exchange transfusion reported for life-threatening methemoglobinemia refractory to methylene blue 1
Critical Time-Sensitive Considerations
The two patients who survived large ingestions both received methylene blue early in their clinical course, while all three fatalities had delayed or no methylene blue administration. 2 This underscores that methylene blue is a time-sensitive antidote where minutes matter.
Prehospital Management
- Contact Poison Control Center immediately upon suspicion 3, 6
- Prenotify receiving emergency department to prepare methylene blue 3
- Some EMS systems are developing prehospital methylene blue protocols given the high mortality 6
Important Contraindications and Warnings
Do NOT Confuse with Sodium Nitrite as Cyanide Antidote
Sodium nitrite is itself used as a cyanide antidote (along with sodium thiosulfate), but this creates a critical distinction: 7, 1
- For cyanide poisoning: Hydroxocobalamin is strongly preferred over sodium nitrite/sodium thiosulfate 7
- For sodium nitrite overdose: You are treating the methemoglobinemia caused BY sodium nitrite, not giving more 1
Methylene Blue Contraindications
Epidemiology and Prevention Context
Intentional sodium nitrite ingestion is an emerging suicide method with increasing incidence since 2017 4. The substance is:
- Readily available online in large quantities 2, 4
- Promoted on suicide forums with specific dosing instructions 2, 4
- Often mistaken for table salt due to similar appearance 5, 4
Estimated lethal dose ranges from 15-113 grams, though survival has occurred after 60-gram ingestion with prompt methylene blue treatment 2.