Anaphylactoid reaction to rattlesnake envenomation.

The clinical manifestations of an anaphylactoid reaction are identical to true anaphylaxis; however, a previous exposure to the offending agent is not needed to manifest these symptoms. We present a case of an anaphylactoid reaction in a 62-y-o female following a first-time envenomation by a rattlesnake. The patient required s.c. epinephrine and i.v. diphenhydramine, methylprednisolone, and ranitidine. She had not been envenomated by a rattlesnake previously or received any horse-derived antivenins in the past.