Cyanide release from sodium nitroprusside in the dog

Area of Science:

• Pharmacology
• Toxicology
• Veterinary Medicine

Background:

• Sodium nitroprusside is a potent vasodilator used clinically.
• Its metabolism can release cyanide, a toxic byproduct.
• Understanding nitroprusside's toxicity and potential antidotes is crucial.

Purpose of the Study:

• To investigate the dose-dependent toxicity of sodium nitroprusside in dogs.
• To evaluate the protective effect of methemoglobin against nitroprusside-induced cyanide toxicity.
• To characterize the pharmacokinetics of cyanide release and detoxification.

Main Methods:

• Administered low and high doses of sodium nitroprusside to dogs over one hour.
• Tested nitroprusside administration with and without prior methemoglobin treatment.
• Measured arterial pressure, metabolic parameters, and blood/tissue cyanide levels.

Main Results:

• High-dose nitroprusside ( > 1.0 mg/kg) caused significant metabolic alterations and decreased oxygen extraction.
• Methemoglobin pretreatment completely prevented nitroprusside toxicity, even at high doses.
• Cyanide was rapidly released from nitroprusside, forming cyanmethemoglobin; detoxification occurred but was insufficient at high doses without methemoglobin.

Conclusions:

• Sodium nitroprusside causes acute cyanide toxicity in dogs at doses > 1.0-1.5 mg/kg.
• Cyanide release from nitroprusside is rapid and substantial.
• Methemoglobin effectively protects against nitroprusside-induced cyanide toxicity in dogs.