Identifying Patients with Cyanide Poisoning

Cyanide poisoning may result from inhalation, ingestion, or dermal exposure to various cyanide-containing compounds, including smoke from closed-space fires. Sources of cyanide poisoning include hydrogen cyanide and its salts, cyanogenic plants, aliphatic nitriles, and prolonged exposure to sodium nitroprusside.

The presence and extent of cyanide poisoning are often initially unknown. There is no widely available, rapid, confirmatory cyanide blood test. Treatment decisions must be made on the basis of clinical history and signs and symptoms of cyanide intoxication.

In some settings, panic symptoms including tachypnea and vomiting may mimic early cyanide poisoning signs. The presence of altered mental status (e.g., confusion and disorientation) and/or mydriasis is suggestive of true cyanide poisoning although these signs can occur with other toxic exposures as well.

Smoke Inhalation

Not all smoke inhalation victims will have cyanide poisoning and may present with burns, trauma, and exposure to other toxic substances making a diagnosis of cyanide poisoning particularly difficult. Prior to administration of NITHIODOTE, smoke-inhalation victims should be assessed for the following:

• Exposure to fire or smoke in an enclosed area
• Presence of soot around the mouth, nose, or oropharynx
• Altered mental status

Although hypotension is highly suggestive of cyanide poisoning, it is only present in a small percentage of cyanide-poisoned smoke inhalation victims. Also indicative of cyanide poisoning is a plasma lactate concentration greater than or equal to 10 mmol/L (a value higher than that typically listed in the table of signs and symptoms of isolated cyanide poisoning because carbon monoxide associated with smoke inhalation also contributes to lactic acidemia). If cyanide poisoning is suspected, treatment should not be delayed in order to obtain a plasma lactate concentration.

Use with Other Cyanide Antidotes

The safety of administering other cyanide antidotes simultaneously with NITHIODOTE has not been established. If a decision is made to administer another cyanide antidote with NITHIODOTE, these drugs should not be administered concurrently in the same intravenous (IV) line. [see Dosage and Administration (2.2)]

Methemoglobin level: Administrations of sodium nitrite solely to achieve an arbitrary level of methemoglobinemia may be unnecessary and potentially hazardous. The therapeutic effects of sodium nitrite do not appear to be mediated by methemoglobin formation alone [see Clinical Pharmacology (12)] and clinical responses to sodium nitrite administration have been reported in association with methemoglobin levels of less than 10%. Administration of sodium nitrite beyond the initial dose should be guided primarily by clinical response to treatment (i.e., a second dose should be considered only if there is inadequate clinical response to the first dose). It is generally recommended that methemoglobin concentrations be closely monitored and kept below 30%. Monitor serum methemoglobin levels during treatment using co-oximetry, and discontinue administration of sodium nitrite when methemoglobin levels exceed 30%. Intravenous methylene blue and exchange transfusion have been reported in the literature as treatments for life-threatening methemoglobinemia.