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In a patient with presumed cyanide poisoning, the adult dose of sodium thiosulfate is 12.5 g (50 mL of 25% solution) administered intravenously either as a bolus injection or infused over 10 to 30 minutes, depending on the severity of the situation.9 The dose of sodium thiosulfate can be repeated at half the initial dose if manifestations of cyanide toxicity reappear or at 2 hours as prophylaxis.9
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In situations where the formation of methemoglobin by a nitrite would not be harmful, intravenously inject 300 mg sodium nitrite (10 mL of 3% solution) at a rate of 2.5 to 5 mL/min prior to administration of sodium thiosulfate. The same needle and vein can be used. The dose of sodium nitrite can be repeated at half the initial dose if manifestations of cyanide toxicity reappear or at 2 hours as prophylaxis.9
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Amyl nitrite can be used prior to IV administration of sodium nitrite, but only as a temporizing measure until IV sodium nitrite can be administered. Break one amyl nitrite ampule and hold it in front of the patient's mouth for 15 seconds on and 15 seconds off.9 Inhalation of amyl nitrite should be discontinued prior to administration of sodium nitrite.
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In situations where the additional formation of methemoglobin would be harmful, as in patients in whom carboxyhemoglobin or methemoglobin may be present from smoke inhalation from a fire, the nitrite can be withheld and only the sodium thiosulfate administered. Since hydroxocobalamin is now available in the United States, combined therapy of hydroxocobalamin with sodium thiosulfate, which is synergistic, would be ideal. The initial dose of hydroxocobalamin in adults is 5 g (2 × 2.5 g vials) IV over 15 minutes with a second dose administered if warranted.10 Care must be taken not to administer the hydroxocobalamin and sodium thiosulfate through the same IV line since a physical incompatibility occurs, inactivating the hydroxocobalamin.
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The dose of sodium thiosulfate in children is 7 g/m2 up to the adult dose9 or 0.5 g/kg (2 mL/kg of 25% solution) up to the adult dose of 12.5 g (50 mL of 25% solution).22 The dose can be repeated at half the initial dose if manifestations of cyanide toxicity reappear or at 2 hours as prophylaxis.9
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In situations where the formation of methemoglobin by a nitrite would not be harmful, intravenously inject 3% sodium nitrite solution at 6 to 8 mL/m2 (approximately 0.2 mL/kg), not to exceed 10 mL or 300 mg, prior to administration of sodium thiosulfate.9 The same needle and vein can be used. A 0.2-mL/kg dose of 3% sodium nitrite solution is approximately 6 mg/kg sodium nitrite. Based on an in vitro calculation, this dose would be safe for a child with a hemoglobin of 7 g/dL in the absence of other factors that could compromise hemoglobin oxygen saturation, such as carboxyhemoglobin, methemoglobin, or sulfhemoglobinemia.3 The dose of sodium nitrite can be repeated at half the initial dose if manifestations of cyanide toxicity reappear or at 2 hours after the first dose as prophylaxis.9
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Amyl nitrite can be used prior to IV administration of sodium nitrite, but only as a temporizing measure until IV sodium nitrite can be administered. Break one amyl nitrite ampule and hold it in front of the patient's mouth for 15 seconds on and 15 seconds off. Amyl nitrite inhalation should be discontinued prior to administration of sodium nitrite. The healthcare provider must not inhale the amyl nitrite.
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In situations where additional formation of methemoglobin would be harmful, as in patients with smoke inhalation from a fire, the nitrite can be withheld and only the sodium thiosulfate administered. Since hydroxocobalamin is now available in the United States, combined therapy of hydroxocobalamin with sodium thiosulfate, which is synergistic, would be ideal. Although there is no approved US pediatric dose, 70 mg/kg of hydroxocobalamin has been used outside of the United States.10 Care must be taken not to administer the hydroxocobalamin and sodium thiosulfate through the same IV line since a physical incompatibility occurs, inactivating the hydroxocobalamin.
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Nitroprusside-Induced Cyanide Toxicity
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Canine experiments reveal that when the nitroprusside infusion rate is greater than 0.5 mg/kg/h, cyanide concentrations in the blood begin to rise. Coadministration of sodium thiosulfate with sodium nitroprusside in a 5:1 molar ratio (because nitroprusside contains five cyanide ions) prevents the rise in cyanide concentration.22 The usual dosage of sodium nitroprusside is 3 μg/kg/min (range 0.25–10 μg/kg/min).18 Each mole of nitroprusside has a molecular weight of 298 Da including the sodium dehydrate and contains five cyanide ions. A 70-kg person administered 3 μg/kg/min would receive 12.6 mg/h of nitroprusside. This would require 52.4 mg of sodium thiosulfate per hour to detoxify the five cyanide ions liberated from nitroprusside. Prolonged infusion or doses in excess of the body's detoxifying capability may lead to thiocyanate or cyanide toxicity. Some authors recommend adding 0.5 g sodium thiosulfate to each 50 mg of nitroprusside.19 This dose of sodium thiosulfate usually is sufficient to prevent cyanide toxicity from nitroprusside; however, thiocyanate may accumulate, especially in patients with renal insufficiency. Although thiocyanate is relatively nontoxic compared to cyanide it may produce dose-dependent tinnitus, miosis, hyperreflexia, and hypothyroidism, especially at serum concentrations greater than 60 μg/mL,18 and thiocyanate is hemodialyzable. Nitroprusside-induced cyanide toxicity should be treated like cyanide toxicity from any other cause: stop the nitroprusside dosage and administer sodium thiosulfate, sodium nitrite, or hydroxocobalamin (if available) according to the doses and precautions listed.