Consultation with a medical toxicologist or other physician with expertise and prior experience treating venomous snake bites is strongly encouraged before initiating antivenom therapy for bites by Crotalinae snakes found in North America (rattlesnakes, water moccasins [cottonmouths], and copperheads). Emergency consultation with a medical toxicologist in the United States is available at 1-800-222-1222. | |||
Antivenom | |||
Crotalidae immune equine F(ab')2 (Fab2AV, Anavip) | Polyvalent Crotalinae ovine immune Fab (FabAV, CroFab) | ||
Initial dose* |
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Maintenance doses? | No: Patient should be observed for an additional 18 hours after control achieved | Yes: 2 vials every 6 hours for 3 doses | |
As-needed doses for recurrent venom effects | 4 vials | 2 vials | |
Timeline for reassessment of platelets and fibrinogen |
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Indications for antivenom treatment of Crotalinae envenomation include swelling that extends beyond the bite site or is progressing; face or neck bites with any swelling; hemotoxicity (thrombocytopenia, hypofibrinogenemia, or prolonged prothrombin time [PT]); or other systemic toxicity such as bleeding, shock, myokymia (rippling muscle movement of the face and extremities), and/or, rarely, weakness/paralysis after bites by Mohave or Southern Pacific rattlesnakes. Coagulation testing should include complete blood count with a focus on the platelet count, PT, international normalized ratio (INR), and plasma fibrinogen at patient presentation. At 4 hours or longer after the bite, some experts also obtain fibrin degradation testing, either D-dimer or fibrin split products, to identify patients whose initial studies do not show significant abnormalities but who remain at risk for delayed hemotoxicity. Antivenom therapy does not affect the results of fibrin degradation tests. For more details, refer to UpToDate content on use of antivenom to manage North American Crotalinae snakebite.
Antivenom administration is associated with potentially severe allergic reactions; it should only occur in a continuously monitored emergency or intensive care unit setting. During administration, the physician should ensure the immediate availability of epinephrine ([concentration 1 mg/mL] 0.3 to 0.5 mg intramuscularly in the anterolateral thigh, [concentration 0.1 mg/mL] prepared for continuous intravenous infusion), diphenhydramine or similar antihistamine, intravenous corticosteroids, and inhaled albuterol.For both antivenoms, do not use if otherwise discolored or turbid.
Once either FabAV or Fab2AV is reconstituted, combine contents of all vials and further dilute to a total of 250 mL sterile normal saline. Infuse within 4 hours of preparation; administer the antivenom as an intravenous infusion at an initial rate of 25 to 50 mL/hour for the first 10 minutes. If tolerated, increase the rate to finish the infusion over 1 hour. If signs of adverse effects (eg, urticaria, lip or tongue swelling, difficulty breathing, or hypotension) develop, immediately stop the infusion. Refer to UpToDate content on treatment of acute reactions caused by North American Crotalinae snake antivenom for further recommendations.
¶ Control of envenomation is achieved when all of the following are present:Do you want to add Medilib to your home screen?