By Dr. Ken Lavelle, MD, NREMT-P
In the past two articles we discussed cyanide poisoning and the difficulties of treating potential cyanide exposure from victims of smoke inhalation. The burning of plastics, fabrics and other synthetic materials creates cyanide, and fire victims often are exposed to cyanide as well as carbon monoxide and other gasses. There are existing treatments for cyanide poisoning, namely the Cyanide Antidote Kit, but this kit cannot be safely used in smoke inhalation victims because the kit itself causes a decrease in the oxygen carrying capacity of the blood. In someone with carbon monoxide exposure this could be fatal. We need another option.
Because there is no specific test or sign of cyanide poisoning, we need a treatment that is safe to give to a victim even if they do not in fact have exposure to cyanide. We need it to be easy to give and transport so it can be given by paramedics in the field. And preferably, we need it to be cheap. Well, 2 out of 3 isn't bad.
To find this treatment, we look across the ocean. The Paris Fire Brigade has been treating victims of smoke inhalation for several years with a substance called hydroxocobalamin. This substance has recently been made available in the United States. It has also been used in Sweden, Japan, Spain and Hong Kong.
Hydroxocobalamin (vitamin B12a) is a natural form of the vitamin B12 that contains a hemoglobin-like molecule with cobalt. It binds to cyanide with such an affinity that it can pull the cyanide out of the mitochondria of the cell to form cyanocobalamin. The mitochondria can then return to its normal function. Cyanocobalamin is then excreted in the urine.
Hydroxocobalamin has a very safe profile. It has been given to numerous volunteers that had no cyanide exposure without any significant adverse effects. It was found to mildly increase blood pressure, not necessarily a bad thing in cyanide exposed patients. It also turns the skin of recipients reddish-orange, which clears in a few days.
In Paris, a study was published based on the results of its use. You can read a PDF report from the study here. Over a 7 year period, it was given to 69 patients. 37 of these were comatose and 15 in cardiac arrest. Fifty of these patients survived, 41 with no long term adverse outcome. Two of the patients in cardiac arrest survived. This is rather significant, especially in light of the fact that in the 63 patients tested for cyanide, 42 had elevated levels. The number of patients treated was low, so we have to be careful about saying this is the standard of care, but the fact that the agent is so safe makes the risk benefit ratio lean towards its use.
Hydroxocobalamin was approved by the FDA for use in the US in 2006 as CyanoKit for known or suspected cyanide poisoned patients. It is supplied in 2 vials, each with 2.5 grams of Hydroxocobalamin. The dose is 5 grams to be given IV over 15 minutes. It can be used in conjunction with Sodium Thiosulfate, which we have discussed previously. The shelf life of the drug is about 30 months, however the cost is significant — approximately $700. Unfortunately, this is common for new drugs that are still "on patent." This high cost will limit its deployment to every ambulance, even if approved by each state for use by paramedics.
It is unlikely to be needed in a patient who is awake and alert and not in acute distress. However, it can be considered for victims from a fire building that are comatose, in severe cardiovascular compromise or in cardiac arrest. If approved in your region, it could be deployed on a supervisor vehicle to limit the cost of stocking it on every ambulance. It will likely become cheaper in the future just as amiodarone did, and its stock and use may become more widespread.
In summary, hydroxocobalamin is a new, safe agent for use in known or suspected victims of cyanide exposure. The cost and approval status may limit its use in your EMS system, but watch for changes in both areas that may permit its use to be implemented.