Dear readers, it is time for the return of the debunker, here to dispel the common myths and misconceptions surrounding snakebite medicine and educate the masses. The topic of our discussion today is antivenom and the goal is to correct many of the rumors that impact patient care. Feel free to ask questions and I will get to them when I can. Without further adieu, let us begin. The questions of the day are as follows:
IS ANTIVENOM ACTUALLY MORE DANGEROUS THAN THE SNAKEBITE ITSELF? WHAT SHOULD I DO IF I AM BITTEN BY A VENOMOUS SNAKE AND AM ALLERGIC TO THE ANTIVENOM?
These are very common questions for those of us who treat snakebite patients, so I would like to take a few minutes to provide some facts about antivenom therapy – especially in light of some of the recent threads we have had on this site.
First of all, for anyone who is too lazy to read the entire post I will give you the following key points upfront:
1. The most important thing to remember is that there are no absolute contraindications to antivenom therapy in a patient with a life-threatening envenomation. Translation: I don’t care how badly you have reacted to antivenom in the past if you are going to die of a snakebite without antivenom in the present. You are going to need the antivenom either way.
2. Antivenom is a safe and effective product that is absolutely life and limb saving in patients with snake envenomations. Antivenom is made from venom, but there is no actual venom in antivenom and it can’t poison you or cause any of the effects of a snakebite. Venom can persist in the body for weeks until it is destroyed by the antivenom, and as long as it remains untreated it is continuing to destroy your soft tissue, blood clotting, and other important parts of your body that you really don’t want it messing with. You can think of the enzymes in viper venom like a bunch of little pac-men set loose in your blood stream that will continue to devour important pieces of your body until they run into the antivenom and get killed.
3. There are two types of adverse reactions you can get from antivenom therapy – early adverse reactions (EARs) and late adverse reactions (also known as serum sickness). Most patients do not get either of these reactions and most of the reactions that occur are mild and can be managed with little more than antihistamines and the occasional short course of oral prednisone. A reaction to the antivenom treatment does not cancel out the benefit of the antivenom or prevent it from doing its job. This is very important!
4. The most dangerous side effect of antivenom is anaphylactic shock, which is a serious and life-threatening allergic reaction. This occurs in only a very small percentage of cases with modern antivenoms, usually less than 2% of patients with the current high-quality antivenoms we have available. The anaphylactic shock produced by antivenoms is the same anaphylactic shock you can get with a peanut allergy and a peanut butter sandwich, and we treat it the same way – epinephrine, antihistamines, and steroids. Anaphylaxis treatment is one of the bread-and-butter skills of emergency medicine and everyone in the profession knows how to treat this, so it’s not like you are going to develop some sort of rare and incredibly complex deadly side effect.
5. With late adverse reactions aka “serum sickness” patients may experience generalized flu-like symptoms (joint pain, muscle pain, fever, malaise) and a rash anywhere from 5 – 21 days after the antivenom was given. This is believed to occur due to an immune response as their body is eliminating the bulk of the antivenom – venom complexes that have precipitated out of the bloodstream and it usually resolves within a week without any treatment. It can also be treated with a short course of steroids if the patient is very uncomfortable, which clears it up very quickly in most cases.
So there you have it folks. The common misconception that antivenom is very dangerous and will cause all sorts of serious problems if injected into a patient who does not need it (or needed a different antivenom) is totally untrue. Worst of all, this factually incorrect belief is widely held by many non-specialist physicians and can lead to under-dosing antivenom in the emergency department or in some cases no antivenom at all for a patient who legitimately needs it. This attitude probably results from the high incidence of serious EARs – sometimes in the realm of 25% – 50% – that occurred in response to the early generations of antivenom produced in the 1900’s – 1950’s. Older antivenoms were not subjected to the rigorous process of purification and fractionation seen in the newer high-quality serums produced by reputable companies today, and consequently reaction rates have been reduced to less than <5% of patients with some of the better antivenoms on the market. Additionally, most of those reactions are mild (itching, hives, cough, etc) that can be managed by nothing more than antihistamines and occasionally steroids.
Last but not least, let’s talk about what happens if you come in with a snakebite and a known allergy to antivenom which is another question I have been asked a lot. When treating an envenomation I always ask whether a patient has ever experienced a prior snakebite, received antivenom therapy, reacted badly to immunizations, etc. However, the truth is that while this is useful information for me to assess the relative likelihood of inducing a severe reaction, it really doesn’t do very much at all to change the primary treatment if the patient is at risk of losing either life or limb due to the snakebite. Anytime you are going to give antivenom you should be prepared for the rare possibility of anaphylaxis and have the tools and medications to treat it ready at the bedside in case they are needed. These tools and medications are cheap and widely available in every ambulance and ER in the country. The right antivenom can work miracles and bring patients back seemingly up until the final moments before death. If you need antivenom for a severe snake envenomation and have a history of severe allergy to antivenom I am going to give you the antivenom and aggressively treat the reaction with epinephrine, antihistamines, and steroids.
As noted earlier, a reaction to the antivenom treatment does not cancel out the benefit of the antivenom or prevent it from doing its job. This is very important! In Africa we often treat patients by pushing the entire dose intravenously in a single bolus over 5 minutes rather than hanging the antivenom in a drip that is infused over a longer period of time. Many of my snakebite patients are carried into the clinics in the middle of the night on the brink of death with severe internal bleeding and rapidly deteriorating vital signs. If I push an intravenous bolus of antivenom and induce a severe reaction the antivenom is still onboard and can begin working to neutralize the venom immediately. I then immediately treat the reaction and that’s that. It gives me enough time to get the entire dose of life-saving antivenom onboard while they still have a pulse. It’s a trade-off that has worked very well in my experience – in all of these cases the anaphylaxis responded to aggressive treatment and the patient walked out of the hospital a week or so later. In the United States where antivenom is typically given by IV infusion, the infusion is stopped temporarily, the reaction is treated, and then the infusion is resumed. The end result is the same either way – get the antivenom into the patient and treat a reaction if it occurs.
Bottom line is that antivenom is a safe, effective, lifesaving medication that suffers from a bad reputation due to the frequent reactions old products used to cause over 100 years ago and the widespread misinformation about snakebite medicine that persists to this day. Those of us who use it regularly can personally attest to the incredible ability it has to bring back patients who seem unlikely to survive, and we hope that this post will help to dispel some of the pervasive myths that prevent people from receiving the critical treatment they need. Thanks for reading!
I will leave you with a quote from the late great James Ashe of Bio-Ken:
“Antivenom is like the Texan’s gun…He doesn’t need it often, but when he does he needs it real bad.”
