Pharmacology. Sodium nitrite injectable solution and amyl nitrite crushable ampules for inhalation are components of the cyanide antidote package. The value of nitrites as an antidote to cyanide poisoning is twofold: They oxidize hemoglobin to methemoglobin, which binds free cyanide, and they may enhance endothelial cyanide detoxification by producing vasodilation. Inhalation of an ampule of amyl nitrite produces a methemoglobin level of about 5%. Intravenous administration of a single dose of sodium nitrite is anticipated to produce a methemoglobin level of about 20–30%.

Indications

1. 
   

   Symptomatic cyanide poisoning (See Cyanide). Nitrites are not usually used for empiric treatment unless cyanide is suspected very strongly, and they are not recommended for smoke inhalation victims.

   
   
2. 
   

   Nitrites are possibly effective for hydrogen sulfide poisoning if given within 30 minutes of exposure (See Hydrogen Sulfide).

Contraindications

1. 
   

   Significant preexisting methemoglobinemia (>40%).

   
   
2. 
   

   Severe hypotension is a relative contraindication because it may be worsened by nitrites.

   
   
3. 
   

   Administration to patients with concurrent carbon monoxide poisoning is a relative contraindication; generation of methemoglobin may further compromise oxygen transport to the tissues. Hydroxocobalamin (See Hydroxocobalamin) has supplanted nitrites for smoke inhalation victims (patients often have mixed carbon monoxide and cyanide poisoning) in countries where it is available.

Adverse effects

1. 
   

   Headache, facial flushing, dizziness, nausea, vomiting, tachycardia, and sweating may occur. These side effects may be masked by the symptoms of cyanide poisoning.

   
   
2. 
   

   Rapid intravenous administration may result in hypotension.

   
   
3. 
   

   Excessive and potentially fatal methemoglobinemia may result.

   
   
4. 
   

   Use in pregnancy. No assigned FDA category. These agents may compromise blood flow and oxygen delivery to the fetus and may induce fetal methemoglobinemia. Fetal hemoglobin is more sensitive to the oxidant effects of nitrites. However, this does not preclude their acute, short-term use for a seriously symptomatic patient (See Introduction in Section III).

Drug or laboratory interactions

1. 
   

   Hypotension may be exacerbated by the concurrent presence of alcohol or other vasodilators or any antihypertensive agent.

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