Crotaline envenomation

(Redirected from Rattlesnake)


  • The Crotalinae subfamily of Viperidae classifies the new world vipers, or pit vipers. The snakes have a pitlike depression behind the nostril that contains a heat-sensing organ used to find prey.
  • Includes rattlesnakes and copperheads
  • Venom causes local tissue injury, coagulopathy,and thrombocytopenia
  • Up to 25% of bites are dry bites

Common Crotaline (Pit Viper) snake names

  • Rattlesnake
  • Cottonmouth
  • Copperhead
  • Sidewinder
  • Water moccasin
  • Massasauga


  • Venom form a Crotaline mainly damages local tissue via metalloproteinases and hyaluronidase which cause swelling edema and damage to capillaries.
  • Clinical effects consist of:

Clinical Features

  • Fang marks, localized pain, progressive edema extending from bite site
  • Nausea/vomiting
  • Oral numbness/tingling
  • Dizziness
  • Muscle fasciculations
  • Coagulopathy
    • Ecchymoses may appear within minutes to hours

Differential Diagnosis

Envenomations, bites and stings


  • Local injury (pain, progressive swelling, compartment syndrome, lymphangitic spread with pain in the axillae for upper extremity bites or pain in the inguinal region for lower extremity)
    • Track progressive edema of the bitten extremity Q2H until progression stops
    • Mark on the patient a point in the mid-foot, mid-calf, and mid-thigh (lower extremity bite) vs mid-hand, mid-forearm, and mid-humerus (upper extremity bites) to ensure consistency between measurements.
  • Hematologic abnormality (thrombocytopenia, prolonged PT, hypofibrinogenemia) - DIC-like syndrome
  • Systemic effects (hypotension resulting from third spacing)


  • CBC
  • Coags
  • Fibrinogen
  • Chemistry


Local Care

  • Do:
    • Remove all jewelry
    • Mark the leading edge of erythema/edema
  • Do not:
    • Attempt to suck out the venom
    • Place the affected part in cold water
    • Use a tourniquet or wrap
    • Antivenom is first line treatment for compartment syndrome; fasciotomy is last resort if elevated pressures persist.

Antivenom administration

  • See below

Supportive care

  • IVF and vasopressors if needed for hypotension
  • Blood products rarely needed
  • Consider early intubation for head and neck envenomations. High risk for edema and airway compromise.

Crotalidae Polyvalent Immune Fab (FabAV) Antivenin (Crofab)


The following are criteria for administration after Crotalidae bite[1]

  • Progression of swelling
  • Abnormal results on lab tests (platelet < 100,000 or fibrinogen < 100)
  • Systemic manifestations (unstable vitals or altered mental status)

Initial Administration

  • Initial dose: 6 vials[2]
  • Typically diluted into 250 cc or 1 L of normal saline and infused over an hour
  • Same dose for both adults and pediatrics (may have to adjust the dilution of CroFab for small children so that they are not volume overloaded)

Maintenance therapy

  • May repeat dose (2 vials) at 6, 12, and 18 hours later if symptoms not controlled[3]
    • Maintance therapy may be indicated after initial dosing based on local protocols even if control is achieved.[4]

Envenomation control measurement

  • Observe for progression of envenomation during and after antivenom infusion
  • Measure limb circumference at several sites above and below bite
  • Mark advancing border of edema q30min
  • Repeat labs q4hr or after each course of antivenom (whichever is more frequent)

Side Effects

  • Acute allergic reactions occur in <10% pts
    • If occurs stop infusion and give epinephrine/antihistamines if needed
  • Recurrent thrombocytopenia has been described up to 2 weeks after transfusion with FabAV and is likely a result of isolated renal clearance of FabAV and persistent presence of actual venom in serum.[5]
    • Warrants close monitoring of platelets by primary physician or return visit after discharge
  • Serum sickness is unlikely but precautions should be given to patents upon discharge

Crotalinae equine immune F(ab')2 antivenom (Anavip)[6]

  • Approved in 2015 for use in N. American pit viper envenomations.
  • Similar treatment indications
  • Given as 10 vials IV
    • Repeated Q1H as needed for initial control until local signs of envenomation are not progressing, systemic symptoms are resolved, and coagulation and other laboratory parameters have normalized or are trending toward normal.
  • 4 Vials IV maintenance dosing PRN for recurrence of symptoms.
  • Longer half life thought to reduce need for readministration and may reduce risk of recurrent subacute coagulopathy and bleeding vs Crofab [7]


  • Observe all snakebite patients for at least 6hr before determining patient disposition
    • Bites that initially appear innocuous and labs normal at presentation can be deceptive
  • Discharge if symptom-free after 6hr
  • Admit all patients receiving antivenom to the ICU

See Also


  1. Crofab treatment agorithmn
  2. Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
  3. Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
  4. Crofab treatment agorithmn
  5. Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.
  6. FDA Insert -ANAVIP
  7. Bush SP, Ruha AM, Seifert SA, et al. Comparison of F(ab')2 versus Fab antivenom for pit viper envenomation: a prospective, blinded, multicenter, randomized clinical trial. Clin Toxicol (Phila). 2015;53(1):37-45. doi:10.3109/15563650.2014.974263