Shelf Life of Antivenom

A reader asks: "What's the shelf life of antivenom and does it have to be refrigerated? Can I take it hiking?" This is a common and important question. To answer the first question, for the newest North American antivenom product, CroFab™ [Crotalidae Polyvalent Immune Fab (Ovine)], used for treatment of pit viper (e.g., rattlesnake) bites, the antivenom is provided in vials that contain the antivenom, which is mostly composed of fragile proteins, in lyophilized ("freeze-dried") form. The freeze-dried product has a shelf life of 2 to 3 years when stored protected from light and in a cool place (at a temperature of 2 to 8 degrees C, or 36 to 48 degrees F). To administer the antivenom to a human, the health care provider mixes ("reconstitutes") it with liquid, so that it can be injected into a vein of the recipient. Once it is reconstituted, it must be used within a few hours or it loses its effectiveness.

The second question is more important. Should you carry it with you when hiking, presumably for administration in the field in the event of a snake bite? That question is sometimes asked by medical professionals. The answer to them is that it depends on the snakes that might be encountered, which antivenom they propose to carry, the situation in which it will be deployed, how far they will be from advanced medical care, and their qualifications as health care providers. The traditional answer has always been "No": that is, administering antivenom in the field is considered too dangerous, because there has always been a high risk for a serious (potentially fatal) allergic reaction to antivenom, which is composed of animal (usually horse) serum. The newer antivenom products, like CroFab™, while more pure than the previous products, still carry with them the risk for an allergic reaction when given to a person. So, a doctor must balance the benefit of the antivenom against the risk for the allergic, or other adverse, reaction. The only circumstances of which I am aware when antivenin has been carried to be administered in the field have been where the expedition was traveling into extremely venomous snake country quite far from help or the ability to rapidly evacuate a victim, trained doctors were present to administer the antivenom and to treat any adverse reaction, proper medical equipment was carried, and persons experienced in identification of indigenous medical snakes and snake bite treatment were present. Even then, it is done with trepidation, because the mantra is always, "First, do no harm," and a bad allergic reaction to antivenom could easily be much worse than the effects of a snake's venom.

So, for a layperson, the answer remains, "No - do not take antivenom with you on a hike." However, always have a plan for what you will do in the event that you or someone with you becomes bitten by a venomous snake. This generally means a plan for rapid transport to a hospital where antivenom can be given, if necessary, by trained medical professionals.