By Dr. Ken Lavelle, MD, NREMT-P
Cyanide is deadly. It can be encountered in either terrorism or a building fire, but the signs and symptoms are vague. What can we do about it? We need a treatment that is cheap (so it can be on all first line EMS units), safe (so it can be given by a paramedic and not hurt the victim even if they have not been exposed) and easy to give.
Unfortunately, even today, this ideal treatment does not exist.
In the hospital, a common treatment is the Cyanide Antidote Kit. It is also known as the Lilly Kit, Pasadena Kit or the Taylor Kit. These are in short supply — often there is only one or two available to each emergency department. The kit contains three drugs. First, there is Amyl Nitrite for inhalation. Next, there is Sodium Nitrate for IV administration. Finally, there is Sodium Thiosulfate.
One of the treatments for cyanide poisoning is to turn some of the hemoglobin in the body into a form that will attach to cyanide. This will pull the cyanide out of the mitochondria of the cells and allow the resumption of normal energy production. The downside of creating this form of hemoglobin, called methemoglobin, is that it cannot carry oxygen. Normally we want to create about 30 percent methemoglobin.
In patients that have been exposed to cyanide only, this would be fine — the body can survive with only 70 percent of hemoglobin functioning to carry oxygen. However, if the victim has been exposed to carbon monoxide from a house fire, they will have even less functional hemoglobin as carboxyhemoglobin, which is created from exposure to CO, cannot carry oxygen either. The creation of methemoglobin in this situation would likely be fatal.
Amyl Nitrite and Sodium Nitrate create methemoglobinemia, and can be given if there is no exposure to carbon monoxide. If there has, they should not be used. They are not in the typical formulary for EMS providers, and the most common cyanide exposure for EMS is likely to be a house fire when they should not be used anyway.
In addition, there are security concerns as Amyl Nitrate, which is supplied in ampoules for inhalation before an IV can be started, has been reported to be used for aphrodisiac purposes. It tends to disappear from stocks as a result. Finally, the cost of the kit is more than $300, costly for large services with many ambulances.
The third drug in the kit, Sodium Thiosulfate, helps the body detoxify the cyanide. The body can be routinely exposed to small amounts of cyanide and needs to be able to handle this small amount on an everyday basis. There is an enzyme that converts cyanide to a form that can be eliminated from the body.
However, if there is too much cyanide, then this enzyme is overwhelmed. The enzyme uses thiosulfate to convert the cyanide. If we provide more thiosulfate, then this enzyme can detoxify more cyanide.
As EMS cannot really use the first two drugs in the Cyanide Antidote Kit for a smoke inhalation victim for reasons mentioned before, it has been proposed that perhaps the third drug, Sodium Thiosulfate, can be given alone. It is fairly cheap and safe to give.
If given too quickly in a patient with kidney problems, it may cause tinnitus, blurry vision, delirium or seizures -- but compared to death from cyanide poisoning, this can be handled and the benefit exceeds the risk. Research has shown that providing thiosulfate accelerates the conversion of cyanide to a safer form three to four times as quick.
The only drawback to thiosulfate is that is it slow. It is unlikely to help a patient already in cardiac arrest, but it is reasonable to try it even in these cases. It should be given early, before this occurs.
Sodium Thiosulfate is administered IV, 12.5 grams (50mL) over one to two minutes. For children, it should be weight based, given 1.65 mL/kg (of 25 percent solution) over 10 minutes. The cost is about $25 per bottle.
The low cost is one of the benefits. There is a new treatment out that was approved two years ago, the Cyanokit, but it is very expensive – more than $800. While it is very promising, the cost will prevent it being stocked on most EMS units, at least until the price decreases. I’ll discuss the Cyanokit in a future article.
As always, follow local protocol, but look into whether this Sodium Thiosulfate is permitted in your region and discuss with your medical director about adding it to your armamentarium, especially for treating victims from house fires. It may not be ideal, but until other treatments become more affordable, it may be the best chance we have for patients potentially exposed to cyanide.