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Crotalidae Immune F(ab')2 (Equine)

Generic name: antivenin (crotalidae) polyvalent systemic

Brand names: Antivenin Polyvalent, CroFab, Anavip

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Solution Reconstituted, Intravenous:

Anavip: (1 ea) [contains cresol]


Mechanism of Action

Contains venom-specific F(ab’)2 fragments of immunoglobulin G (IgG) that bind and neutralize venom toxins, facilitating redistribution away from target tissues and elimination from the body.



Vdss: 3.3 L

Half-Life Elimination

~5.5 days

Use: Labeled Indications

Rattlesnake envenomation: Management of adult and pediatric patients with North American rattlesnake envenomation


There are no contraindications listed within the manufacturer's labeling.

Dosage and Administration

Dosing: Adult

Rattlesnake envenomation: IV: Note: Initiate therapy as soon as possible after a rattlesnake bite in patients exhibiting any signs of envenomation.

Initial: Ten vials; may repeat every hour as needed until local signs of envenomation are not progressing, systemic symptoms are resolved and coagulation parameters have normalized or are trending toward normal. There is no known maximum dose.

Maintenance: Four vials as needed; may administer for any re-emerging symptoms, including coagulopathies

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Note: Initiate therapy as soon as possible after a rattlesnake bite in patients exhibiting any signs of envenomation.

Rattlesnake envenomation: Infants, Children, and Adolescents: IV:

Initial: Ten vials; may repeat every hour as needed until local signs of envenomation are not progressing, systemic symptoms are resolved, and coagulation parameters have normalized or are trending toward normal.

Maintenance: Four vials as needed; may administer for any reemerging symptoms, including coagulopathies


Reconstitute the contents of each vial with 10 mL of sterile normal saline; gently swirl to mix. The solution should be clear to yellow/green and opalescent. Do not use if otherwise discolored or turbid. Dilute dose (eg, 10 vials) to a total volume of 250 mL with sterile normal saline.


IV: Infuse intravenously over 60 minutes. Infuse at a rate of 25 to 50 mL/hour for the first 10 minutes, carefully monitoring for any allergic reactions. If no reactions occur, increase the infusion rate to 250 mL/hour until completion. Discontinue the infusion if any allergic reaction occurs and institute appropriate emergency treatment. Reassess the risk to benefit ratio before continuing the infusion.


Store at room temperature (up to 25 ºC [77ºF]). Brief temperature excursions are permitted up to 40ºC (104ºF). Do not freeze. Discard partially used vials.

Drug Interactions

There are no known significant interactions.

Adverse Reactions

Frequency not always defined.

Cardiovascular: Peripheral edema (8%)

Central nervous system: Headache (6%), chills (4%), anxiety (2%), insomnia (2%)

Dermatologic: Pruritus (43%), skin rash (12%), skin blister (5%), erythema (4%)

Endocrine & metabolic: Dehydration (2%)

Gastrointestinal: Nausea (23%), vomiting (6%)

Hematologic & oncologic: Thrombocytopenia (1%)

Hypersensitivity: Hypersensitivity

Neuromuscular & skeletal: Arthralgia (11%), myalgia (7%), limb pain (6%)

Respiratory: Dyspnea (1%)

Miscellaneous: Fever (5%)


Concerns related to adverse effects:

  • Acute hypersensitivity reactions: Derived from equine (horse) immune globulin F(ab’)2 fragments; anaphylaxis and anaphylactoid reactions are possible, especially in patients with known allergies to horse protein. Patients who have had previous treatment with Crotalidae immune F(ab’)2 or other equine-derived antivenom/antitoxin may be at a higher risk for hypersensitivity reactions. In patients who develop an anaphylactic reaction, discontinue the infusion and administer emergency care. Immediate treatment (eg, epinephrine 1 mg/mL, corticosteroids, diphenhydramine) should be available.
  • Delayed serum sickness: Delayed serum sickness may occur, usually within 2 weeks; monitor patients with follow-up visits for signs and symptoms (eg, arthralgia, fever, myalgia, pruritus, rash, urticaria).

Dosage form related issues:

  • Cresol: Product may contain small amounts of cresol resulting from the manufacturing process; local reactions and generalized myalgias may occur.
  • Disease transmission: Product derived from equine (horse) plasma; may potentially contain infectious agents (eg, viruses) which could transmit disease.

Monitoring Parameters

Vital signs; CBC, platelet count, prothrombin time, aPTT, fibrinogen levels, fibrin split products, clot retraction, bleeding and coagulation times, BUN, electrolytes, bilirubin (prior to administration and at regular intervals to gauge response to therapy and anticipate additional dosage requirement); size of bite area (repeat every 15 to 30 minutes); intake and output; signs and symptoms of anaphylaxis/allergy. Following the initial control of signs and symptoms, CBC, platelet counts, and clotting studies are evaluated at 6- to 8-hour intervals until patient is stable (Lavonas 2011). The manufacturer recommends monitoring patients in a health care setting for at least 18 hours following initial control of signs and symptoms.


Pregnancy Risk Factor


Pregnancy Considerations

Animal reproduction studies have not been conducted. In general, the health and prognosis of the mother should be taken into consideration when using medications as antidotes; they should be administered to pregnant women if there is a clear indication for use and should not be withheld because of fears of teratogenicity (Bailey 2003). Experience with the use of antivenom in pregnancy is limited; however, treatment with antivenom should be considered in snake envenomations in which it is usually required as definitive management or in envenomations refractory to supportive care (Brown 2013).

Patient Education

  • Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)
  • Patient may experience nausea, vomiting, itching, or painful extremities. Have patient report immediately to prescriber signs of bleeding (vomiting blood or vomit that looks like coffee grounds; coughing up blood; blood in the urine; black, red, or tarry stools; bleeding from the gums; abnormal vaginal bleeding; bruises without a reason or that get bigger; or any severe or persistent bleeding), mood changes, severe headache, vision changes, severe dizziness, passing out, muscle pain, joint pain, or swelling of arms or legs (HCAHPS).
  • Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

Source: Wolters Kluwer Health. Last updated October 16, 2019.