Crofab Side Effects Center

Last updated on RxList: 10/25/2021
Crofab Side Effects Center

What Is Crofab?

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).

What Are Side Effects of Crofab?

Common side effects of CroFab include:

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

Less common side effects of CroFab include:

Dosage for Crofab

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.

What Drugs, Substances, or Supplements Interact with Crofab?

CroFab may interact with other drugs. Tell your doctor all medications and supplements you use.

Crofab During Pregnancy or Breastfeeding

During pregnancy, CroFab should be used only if prescribed. It is unknown if this drug passes into breast milk. Consult your doctor before breastfeeding.

Additional Information

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.


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Crofab Consumer Information

Get emergency medical help if you have signs of an allergic reaction: hives, itching, redness; wheezing, trouble breathing; feeling light-headed; swelling of your face, lips, tongue, or throat.

Some side effects may occur during the injection. Tell your caregiver right away if you feel feverish or nauseated, or if you have low back pain or trouble breathing.

Call your doctor at once if you have:

  • easy bruising, unusual bleeding (nosebleeds, bleeding gums, bleeding from an injury);
  • purple or red pinpoint spots under your skin;
  • fever, swollen glands, rash or itching, joint pain, or general ill feeling;
  • heavy menstrual bleeding; or
  • itching, rash, or skin redness several days after you were treated with Crotalidae antivenin.

Common side effects may include:

  • itching;
  • rash;
  • nausea; or
  • back pain.

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.

Read the entire detailed patient monograph for Crofab (Crotalidae Polyvalent Immune Fab Ovine)


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Crofab Professional Information


Adverse reactions that occurred in ≥5% of subjects were urticaria, rash, nausea, pruritus and back pain.

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 trials of another drug and may not reflect the rates observed in clinical practice.

  • The most common adverse reactions reported in the clinical studies were urticaria, rash and nausea. Adverse reactions involving the skin and appendages (primarily rash, urticaria, and pruritus) were reported in 12 of the 42 patients (Table 1).
  • Of the 19 patients who experienced adverse reactions, 3 patients experienced severe or serious adverse reactions.
    • The 1 patient who experienced a serious adverse reaction 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 urticaria 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 Reactions in Studies of CROFAB by Body System

Advers e Reaction n=42*
Number of Events
Body as a Whole
Back pain 2
Allergic reaction 1
Serum sickness 1
Serum sickness
Urticaria 7
Rash 3
Pruritus 2
Subcutaneous nodule 1
Respiratory System
Cough 1
Digestive System
Nausea 3
Anorexia 1
Coagulation disorder 1
Ecchymosis 1
Myalgia 1
Nervous System
Nervousness 1
*Of the 42 patients receiving CROFAB in the clinical studies, 19 experienced an adverse reaction. A total of 26 adverse reactions was experienced by these 19 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 As s ociated with CROFAB Infus ion)

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 reaction associated with an early serum reaction and 4 experienced an adverse reaction associated with a late serum reaction. Two additional patients were considered to have a late serum reaction by the investigator, although no associated adverse reaction was reported.
**Allergic reaction consisted of urticaria, dyspnea and wheezing in 1 patient.
Serum sickness consisted of severe rash and pruritus in 1 patient.

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.

Postmarketing Experience

The following additional 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:

  • 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
  • Tremor
  • Treatment failure resulting in death

A retrospective study of data collected by the Rocky Mountain Poison and Drug Center for postmarketing use of CROFAB was conducted (see Clinical Studies, Postmarketing Studies).

  • 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.

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

© Crofab Patient Information is supplied by Cerner Multum, Inc. and Crofab Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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