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Crofab Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

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

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)


  • The majority of adverse reactions to CroFab (crotalidae polyvalent immune fab ovine) reported in clinical studies were mild or moderate in severity.
  • 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 6).
  • 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 (crotalidae polyvalent immune fab ovine) therapy due to an allergic reaction.

Table 6. Incidence of Clinical Adverse Events in Studies of CroFab (crotalidae polyvalent immune fab ovine) 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 (crotalidae polyvalent immune fab ovine) 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 (crotalidae polyvalent immune fab ovine) 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 7). In the clinical studies, serum reactions consisted mainly of urticaria and rash, and all patients recovered without sequelae.

Table 7. Incidence of Early and Late Serum Reactions (Reactions Associated with CroFab (crotalidae polyvalent immune fab ovine) 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.

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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