Anaphylactoid (or true anaphylaxis) reactions are exceedingly rare complications of envenomations, but do happen. Risk factors include previous envenomations. Anaphylaxis in first-time envenomations are reported only 3 or 4 times in the medical literature, but may be under-recognized as it's postulated that dermal or GI exposure (i.e. through chronic handling by long-term keepers) may cause the IgE-mediated allergic reaction that we call anaphylaxis. Complicating the picture is that severe envenomations can cause a distributive shock that resembles but is quite distinct from anaphylaxis.
You are much more likely to get anaphylaxis from anti-venom than from the bite itself. Even then, the medical community does not recommend prophylactic administration of epinephrine prior to anti-venom administration. this last point is an active topic of debate, however.
Epi-pens have their place for true anaphylaxis reactions, but probably do more harm than good in the overwhelming majority of envenomations. Signs of anaphlyaxis that mimic signs of envenomation include anxiety, nausea/vomiting, sweating, metallic taste, hypotension. Signs suggestive of anaphylaxis rather than snake bite include hives, generalized itchiness or flushing, generalized swelling (rather than localized to the bite), difficulty breathing (due to airway constriction as well as upper airway swelling). Death from anapylaxis is usually due to airway problems. Death from snakebites (crotalid) is usually due to an overwhelming consumptive coagulopathy and sometimes distributive shock, neither of which improves without neutralization of the venom (although intravenous epi would transiently help the shock). Epi-pen use in the absence of anaphylaxis could potentially exacerbate snake-bites by causing tachycardia (pushing the venom around) and worsening anxiety, as well as the other side effects of the drug.

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• James Bear - Texasbear, Mon Feb 11 14:27:00 2008
• RE: James Bear - Declan123, Mon Feb 11 14:58:31 2008
• RE: James Bear - TexasBear, Mon Feb 11 15:17:33 2008
• RE: James Bear - Declan123, Mon Feb 11 17:25:59 2008
• RE: James Bear - TexasBear, Tue Feb 12 10:01:57 2008
• RE: James Bear - TexasBear, Tue Feb 12 10:04:17 2008
• RE: James Bear - TexasBear, Tue Feb 12 10:05:27 2008
• you guys learn anything from this? - budman 1st, Tue Feb 12 10:45:28 2008
• RE: you guys learn anything from this? - evil-elvis, Tue Feb 12 12:56:41 2008
• RE: you guys learn anything from this? - TJP, Tue Feb 12 13:02:17 2008
• RE: you guys learn anything from this? - armstronmd, Thu Feb 14 14:12:18 2008
• RE: you guys learn anything from this? - Senior, Fri Feb 15 07:43:49 2008
• yes - budman 1st, Mon Feb 18 15:02:47 2008
• RE: yes - Upscale, Tue Feb 19 22:07:37 2008
• RE: yes - Deuce, Wed Feb 20 17:55:20 2008