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Crofab Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 02/21/2017

CroFab [crotalidae polyvalent immune fab) (ovine)] is an antivenin product used as an anti-venom to bites from certain snakes (e.g., rattlesnakes, cottonmouths/water moccasins, copperheads). Common side effects of CroFab include:

  • hives,
  • rash,
  • itching, and
  • nausea.

Less common side effects of CroFab include:

Administration of antivenin should be initiated as soon as possible after crotalid snakebite in patients who develop signs of progressive envenomation (e.g., worsening local injury, coagulation abnormality, or systemic signs of envenomation). The recommended initial dose of CroFab is 4 to 6 vials. CroFab may interact with other drugs. Tell your doctor all medications and supplements you use. During pregnancy, CroFab should be used only if prescribed. It is unknown if this drug passes into breast milk. Consult your doctor before breastfeeding.

Our CroFab [crotalidae polyvalent immune fab) (ovine)] Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Crofab FDA Prescribing Information: Side Effects
(Adverse Reactions)


Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trails of another drug and may not reflect the rates observed in clinical practice.

  • The most common adverse events reported in the clinical studies were urticaria and rash. Adverse events involving the skin and appendages (primarily rash, urticaria, and pruritus) were reported in 14 of the 42 patients (Table 1).
  • Of the 25 patients who experienced adverse reactions, 3 patients experienced severe or serious adverse reactions.
    • The 1 patient who experienced a serious adverse event had a recurrent coagulopathy due to envenomation, which required re-hospitalization and additional antivenin administration. This patient eventually made a complete recovery.
    • The other 2 had severe adverse reactions that consisted of 1 patient who developed severe hives following treatment and 1 patient who developed a severe rash and pruritus several days following treatment. Both patients recovered following treatment with antihistamines and prednisone.
  • One patient discontinued CroFab® therapy due to an allergic reaction.

Table 1 : Incidence of Clinical Adverse Events in Studies of CroFab® by Body System

Adverse Events n=42*
Number of Events
Body as a Whole
Back pain 2
Chest pain 1
Cellulitis 1
Wound infection 1
Chills 1
Allergic reaction† 1
Serum sickness 1
Skin and Appendages
Urticaria 7
Rash 5
Pruritus 3
Subcutaneous nodule 1
Cardiovascular System
Hypotension 1
Respiratory System
Asthma 1
Cough 1
Increased sputum 1
Digestive System
Nausea 3
Anorexia 1
Coagulation disorder 3
Ecchymosis 1
Myalgia 1
Nervous System
Circumoral paresthesia 1
General paresthesia 1
Nervousness 1
* Of the 42 patients receiving CroFab® in the clinical studies, 25 experienced an adverse event. A total of 40 adverse events was experienced by these 25 patients.
† Allergic reaction consisted of urticaria, dyspnea and wheezing in 1 patient.

In the 42 patients treated with CroFab® for minimal or moderate crotalid envenomations, there were 7 events classified as early serum reactions and 5 events classified as late serum reactions, and none were serious (Table 2). In the clinical studies, serum reactions consisted mainly of urticaria and rash, and all patients recovered without sequelae.

Table 2 : Incidence of Early and Late Serum Reactions (Reactions Associated with CroFab® Infusion)

Number of Events
Early Serum Reactions
Urticaria 5
Cough 1
Allergic reaction** 1
Late Serum Reactions
Rash 2
Pruritus 1
Urticaria 1
Serum sickness† 1
* 6 of 42 patients experienced an adverse event associated with an early serum reaction and 4 experienced an adverse event associated with a late serum reaction. Two additional patients were considered to have a late serum reaction by the investigator, although no associated adverse event was reported.
** Allergic reaction consisted of urticaria, dyspnea and wheezing in 1 patient.
† Serum sickness consisted of severe rash and pruritus in 1 patient.

Post-marketing Experience

The following adverse reactions have been identified during the post approval use of CroFab®. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to product exposure:

  • Acute allergic reactions including anaphylaxis or anaphylactoid type reactions during or shortly following CroFab® infusion, manifested by one or more of the following: anxiety, bronchospasm, chills, edema, fever, hypotension, pruritis, rash, urticaria, voice alteration, and/or wheezing
  • Delayed allergic reaction manifested by fever, pruritis and/or rash
  • Delayed or recurrent coagulopathy or thrombocytopenia
  • Failure to achieve initial control
  • Recurrent swelling refractory to treatment
  • Thrombocytopenia refractory to treatment
  • Prolonged hospitalization
  • Bleeding
  • Nausea
  • Tremor
  • Worsening eye sight
  • Treatment failure resulting in death

A retrospective study of data collected by the Rocky Mountain Poison and Drug Center for post-marketing use of CroFab® was conducted (13.2).

  • There were a total of 36 immediate adverse drug reactions reported in 6.1% (15/247) of patients in the post-marketing retrospective study, including one patient in the severely envenomated group (3.6%, n = 28) and 13 patients in the mild/moderate severity group (7.2%, n = 181) (not significantly different rates).
    • There were 11 immediate serious adverse events related to CroFab® administration reported in four patients. The events included two episodes each of hypotension and tongue swelling, and one episode each of chest discomfort, angioedema, bronchospasm, wheezing, tracheal edema, dyspnea, and lip swelling.
    • There were 22 immediate non-serious adverse events related to CroFab® administration reported in 12 patients. The events included four episodes each of rash and pruritis, three episodes of urticaria, and one episode each of tachycardia, tachypnea, erythema, swelling, hyperhidrosis, dizziness, headache, musculoskeletal chest pain, chills, feeling cold, and nervousness.
  • Delayed hypersensitivity reactions were reported for two patients. In one patient the symptoms occurred 6 days post-dosing, were not serious, and described as hives, itching and epigastric pressure. In the second patient symptoms were not described in the medical records and were therefore not captured in this study.
  • Recurrent coagulopathy developed in 5 severely envenomated patients and in 6 mild/moderate envenomated patients. In addition, 7 mild/moderate patients experienced delayed-onset coagulopathy. One severely envenomated patient with recurrent coagulopathy experienced medically significant bleeding.
Additional Published Clinical Studies Experience

From a literature review of nine publications on CroFab® containing patient exposure data, 15 of 313 (4.8%) patients receiving CroFab® experienced acute hypersensitivity reactions.

The most common signs and symptoms associated with these reactions were rash (10 patients) and wheezing (3 patients). Most reactions were mild, resolved after antihistamine therapy, and did not require discontinuation of antivenom therapy. No patient developed a life-threatening hypersensitivity reaction, required intubation, suffered lasting ill-effect, or died as a result of CroFab® administration.

Follow up data (minimum of six days after treatment) were available in 94 of the 313 patients and delayed hypersensitivity reactions were reported in 10 cases. The most common signs and symptoms of delayed hypersensitivity were rash (9 patients) and fever (3 patients). Most were mild and treated with antihistamines and steroids.

Read the entire FDA prescribing information for Crofab (Crotalidae Polyvalent Immune Fab Ovine)

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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