Rattlesnake antivenin

When determining the dosage of antivenin, the victim’s size should be considered because the median lethal dose of venom is based on the milligrams of venom injected and the victim’s weight in kg. Therefore, smaller animals may require larger doses of antivenin. The average antivenin dose for pit viper envenomations is one vial. The labeled dose for Antivenin (Fort Dodge) is 1-5 vials (10-50 ml), IV. If a victim has a severe envenomation (the patient has marked tissue necrosis, is obtund, or is in severe shock), administer 2-5 vials of antivenin IV. Give the entire initial dose of antivenin within one hour. Occasionally, patients bitten by large rattlesnakes may need as many as 10 vials of antivenin. A single vial of antivenin given early is equivalent to several vials given later. This author recommends administering antivenin as soon as a pit viper bite is diagnosed because multiple injections given later are costly. About 85% of dogs and cats bitten by pit vipers have abnormal lab values indicative of moderate or severe envenomations. Although the 15% with only mild envenomations may be overtreated, the advantage to the other 85% is great enough to justify early antivenin use in all pit viper bite victims. Severe allergic reactions occur at a rate of <1%. Michael Peterson, DVM, MSVeterinary Medicine 93:10