Acute Allergic Reactions Associated With CroFab

In the April 2008 issue of Annals of Emergency Medicine appears an article entitled "Acute Hypersensitivity Reactions Associated with Administration of Crotalidae Polyvalent Immune Fab Antivenom," by Robert Cannon, Anne-Michelle Ruha, and John Kashani. These doctors performed a chart review of all patients that had been admitted with the diagnosis of rattlesnake bite to Phoenix Children's Hospital and Banner Good Samaritan Medical Center in Phoenix, Arizona between July 2000 and June 2004.

The chart review yielded 93 patients who were treated with crotalidae polyvalent immune Fab (ovine [sheep]) antivenom (commercially known as CroFab; FabAV, Protherics, Inc., Brentwood, TN). This antivenom is made of "small" antibody fragments in a manner designed to make the antivenom more effective in humans at neutralizing snake venom, while resulting in fewer allergic (adverse) reactions. These 93 patients included 72 males and 21 females. Their mean age was 34.5 years (range 16 months to 91 years), and the mean dose of antivenom administered was 12 vials (range 4 to 32 vials). The incidence of acute hypersensitivity (allergic) reactions was 5 of 93, or 5.4%. In four of the cases, the reaction was mild and easily treated, such that the full course of antivenom could be administered. One patient developed a reaction that necessitated discontinuation of antivenom administration.

These data are even better than the previously reported data with respect to incidence of allergic reactions. Before CroFab came on the scene in 2001, doctors used Antivenin (Crotalidae) Polyvalent from Wyeth Laboratories, which is made from a different process, and was notorious for causing frequent serious allergic reactions. I can recall spending long hours working in the intensive care unit administering this older product to severely envenomed victims, essentially having to infuse a few drops of the antivenin alternated with intravenous epinephrine to counteract the allergic manifestations. It would take many hours to administer the requisite doses of antivenom, and many patients suffered both immediate and delayed allergic reactions. With CroFab, it has become much easier to manage snakebite victims.

As the authors explain, FabAV is produced by immunizing individual flocks of sheep with one of 4 poisonous snake venoms: Eastern Diamondback rattlesnake, Western Diamondback rattlesnake, Mojave rattlesnake, and cottonmouth. Because the sheep are immunized, they develop antibodies, which circulate in their bloodstreams. The serum from their blood is digested with papain, which breaks down the antibodies into fragments, from which the Fab fragments are isolated. Other fragments and extraneous proteins are discarded. The four different types of Fab fragments (one type from each flock of sheep) are combined to create a highly purified product that lacks the immunogenic larger antibody fragments and proteins fround in Antivenin (Crotalidae) Polyvalent. Thus, the final product is much less prone to induce an adverse allergic reaction.

Using the newer antivenom product, fewer patients should have allergic reactions necessitating therapies such as infusion of epinephrine, which will make their care easier and less dangerous.

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Tags: snakebite,CroFab, antivenom, wilderness medicine, outdoor medicine, healthline

Labels: antivenom, CroFab, snake bite, snakebite, venomous snakes

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Myths to Debunk

There are many myths related to outdoor medicine. These need to be “debunked,” so that people do not fall prey to outdated and useless techniques. Here are some of the most common myths (in italix):

1. Mechanical suction, electric shock, and immersion in ice water are effective first aid (“field”) therapies for snakebite. In truth, these are not only not helpful, they may be quite harmful. Antivenom therapy is the only therapy that has been proven effective, with the possible exception of pressure immobilization for certain elapid (e.g., coral) snake bites.
2. Urinating on a jellyfish sting is an effective method to reduce pain. This is of very limited value. Some persons will cite that it was helpful in their particular case, but at least as many persons will state that it did not diminish the pain. The most effective therapy is decontamination with a specific topical compound, such as vinegar or ammonia. The decontaminant chosen depends upon the species of stinging jellyfish.
3. Applying a cold pack to a jellyfish sting is the most effective method to reduce the pain. Current information indicates that application of warmth (e.g., immersion in non-scalding hot water) may be much more beneficial.
4. Rabies shots are injected into the abdomen and are horribly painful. Not true- post exposure rabies vaccination may include a painful component as rabies immune globulin is injected into the bite site, but the subsequent vaccine, which is administered as part of the post exposure treatment, is given as a series of very tolerable injections into the arm or thigh.
5. In any circumstance of frostbite, rapid rewarming is essential. Actually, this should only be done if the body part can be relatively guaranteed to remain thawed. Otherwise, re-freezing the tissue causes significantly more damage than does the initial episode of freezing.
6. The Heimlich maneuver should be used for any victim of submersion (near-drowning) to remove water from the lungs and improve the chance for survival. The Heimlich maneuver has never been proven to be of use in humans in this situation, and may in fact increase the risk for vomiting and harmful inhalation of gastric contents. There is no evidence that it removes water from the lungs.
7. Drinking large amounts of liquids is harmful during exercise because it promotes stomach cramps. Quite the opposite – so long as the ingested amounts are prudent and don’t promote nausea from a full stomach, it is essential to replace fluids and electrolytes constantly during periods of high exertion, particularly in the heat, to avoid dehydration.
8. A person struck by lightning is “electrically charged” and may not be safely touched. This is not true. It is perfectly safe to touch such a person, and in fact the sooner that breathing can be supported, the more likely that the victim will survive with maximal neurological recovery.
9. In cold water, it is better to remain in the water where one feels warm that to pull oneself onto a rescue vessel or platform and be exposed to wind chill. Absolutely not true – one may lose heat 25 times as fast in the water as in air, so no matter how uncomfortable you feel, if it is possible to get out of the water, do so.
10. Sharks and bears are attracted to menstrual blood, so it is important for women to avoid diving and hiking during menstruation. This is a false concept, and has never been proven to be true, either epidemiologically or scientifically.

photo by Jenny Hargrove

Tags: myths,wilderness medicine, outdoor medicine, healthline

Labels: :Heimlich maneuver, bear, drowning, hypothermia, jellyfish, lightning, myths, shark, snakebite, wilderness medicine

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Snakes of Medical Importance in India

With this post, I am going to begin to make regular use of the journal Wilderness & Environmental Medicine, published by the Wilderness Medical Society, in order to bring you cutting edge information. I will condense and translate from articles of interest, so that the knowledge presented can be disseminated beyond the health care providers who are subscribers to the journal. In subsequent posts, I will offer summaries from other important medical journals, such as High Altitude Medicine & Biology, the New England Journal of Medicine, and so forth.

In Wilderness & Environmental Medicine, 18, 2-9 (2007) appears an article entitled Snakes of Medical Importance in India: Is the Concept of the "Big 4" Still Relevant and Useful? by Drs. Ian Simpson and Robert Norris. In this article, they point out that snakebites continue to be a major medical concern in India, but little rigorous epidemiology to support exactly which snakes are the culprits for the majority of envenomations. This is a significant issue, as it has been estimated by the World Health Organization that there may be as many as 50,000 snakebite deaths per year in India.

Traditionally, the snakes of medical importance have been listed as the Indian cobra Naja naja, the common krait Bungarus caeruleus, the Russell's viper Daboia russelii, and the saw-scaled viper Echis carinatus. However, the observation that the hump-nosed pit viper Hypnale hypnale is commonly misidentified as the saw-scaled viper leads the authors to conclude that the hump-nosed pit viper is of medical significance and perhaps should be included in current efforts to develop and refine antivenoms used to treat victims of venomous snakebites. This is particularly important given the fact that the antivenom currently used in India to treat snakebite victims does not appear to be particularly effective against the bite of the hump-nosed pit viper.

The authors further note that hospitals can be a rich source of epidemiological data in order to identify other species of snakes that may be causing severe injuries and death. In North America, we teach snake bite victims to capture and transport venomous snakes with extreme caution, if at all, in order to avoid additional bites. It would appear that in India, it may be more important for biting snakes to be captured and identified, in order for clinicians and snakebite experts to better understand the clinical syndromes associated with the bites of specific snakes, and to better prepare life and limb saving antivenom products.

photo of hump-nosed viper courtesy of Ian Simpson and the Wilderness Medical Society

Tags: snake bite, snakebite, venomous snakebite, antivenom, India, viper, wilderness medicine, outdoor medicine, healthline

Labels: snake bite, snakebite, venomous snakes, viper

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