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Crofab (Intravenous)

Generic name: antivenin (crotalidae) polyvalent immune fab (an-tye-VEN-in (kroe-TAL-i-dee) pol-ee-VAY-lent i-MUNE fab)
Drug class: Antitoxins and antivenins

Medically reviewed by Last updated on Dec 20, 2022.

Uses for Crofab

Pit viper antivenin injection is used to treat the bites of certain venomous snakes called pit vipers (crotalids), which are native to North America. This particular pit viper antivenin is made from the blood of sheep and is used to treat the bites of the following types of pit viper: the Western Diamondback, Eastern Diamondback, and Mojave rattlesnakes, and the Copperhead snake, Cottonmouth, or Water Moccasin.

This medicine is to be given only by or under the direct supervision of your doctor.

Before using Crofab

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of pit viper antivenin injection in children. Safety and efficacy have been established.


Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of pit viper antivenin injection in the elderly.

Breast Feeding

There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Allergy to papaya or to the enzyme papain—Should not be used in patients with this condition, unless management for an allergic reaction is readily available.
  • Allergy to chymopapain, bromelain (pineapple enzyme), dust mite, or latex or
  • Cancer or
  • Collagen disease or
  • Congestive heart failure or
  • Diarrhea or
  • Fever or
  • Liver problems or
  • Poor nutrition status (malnourishment) or
  • Thyroid problems or
  • Vitamin K deficiency—Use with caution. May make these conditions worse.
  • Snake bite, previous—Use with caution. During previous treatment, your body may have developed antibodies (proteins produced by the immune system that help the body fight infection and are involved in allergic reactions), which may cause a serious allergic reaction with the current treatment.

Proper use of Crofab

A nurse or other trained health professional will give you this medicine in a medical facility. It is given through a needle placed into one of your veins. The medicine must be given slowly, so the needle will have to remain in place for at least 60 minutes.

Your doctor will need to watch you for at least one hour after your injection to make sure the medicine is working properly and does not cause unwanted side effects.

Precautions while using Crofab

It is very important that your doctor check your or your child's progress closely while receiving this medicine to make sure this medicine is working properly. Blood tests may be needed to check for unwanted effects.

Check with your doctor right away if you have any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, headache, dizziness, or weakness, pain, swelling, or discomfort in a joint, pinpoint red spots on your skin, unusual nosebleeds, or unusual vaginal bleeding that is heavier than normal. These may be signs of bleeding problems.

This medicine may cause serious allergic reactions, including anaphylaxis, which can be life-threatening and requires immediate medical attention. Tell your doctor right away if you have a rash, itching, hoarseness, trouble breathing, trouble swallowing, or any swelling of your hands, face, or mouth after receiving this medicine.

Side Effects of Crofab

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur:

Less common

  • Bruising
  • cough
  • difficulty in moving
  • difficulty swallowing
  • dizziness
  • fast heartbeat
  • feeling of discomfort
  • fever
  • hives, itching, skin rash
  • joint pain or swelling
  • large, flat, blue or purplish patches in the skin
  • muscle cramps, pain, or stiffness
  • problems with bleeding or clotting
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • swollen lymph glands
  • tightness in the chest
  • unusual tiredness or weakness


  • Blurred vision
  • chest pain or discomfort
  • confusion
  • difficulty breathing
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • fast, pounding, or irregular heartbeat or pulse
  • large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or genitals
  • noisy breathing
  • rapid, shallow breathing
  • sweating

Incidence not known

  • Black, tarry stools
  • bleeding gums
  • blood in the urine or stools
  • itching, swelling, redness, tenderness, or hard lump at the injection site
  • pinpoint red spots on the skin
  • tremor
  • unusual bleeding or bruising

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

  • Back pain
  • loss of appetite
  • nausea
  • nervousness
  • small lumps under the skin
  • weight loss


  • Bone pain
  • feeling cold
  • headache

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.