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Generic name: antivenin (Crotalidae) polyvalent (AN tye VEN in (kroe TAL i dee) POL ee VAY lent)
Brand names: Anavip, CroFab
Drug class: Antitoxins and antivenins

Medically reviewed by on Jul 4, 2022. Written by Cerner Multum.

What is CroFab?

Crotalidae antivenin is an anti-venom used to treat a person who has been bitten by a venomous snake such as a rattlesnake or Water Moccasin.

CroFab may also be used for purposes not listed in this medication guide.


If possible before you receive CroFab, tell your doctor if you are allergic to any foods, animals, or other allergens.

In an emergency situation it may not be possible before you are treated to tell your caregivers about your health conditions or if you are pregnant or breast feeding. Make sure any doctor caring for you afterward knows that you have received this medication.

Before taking this medicine

If possible before you receive Crotalidae antivenin, tell your doctor if you allergic to any foods, animals, or other allergens. Before treating you with this medicine, your caregivers should know if you are allergic to papaya, papain, pineapples, sheep, horses, dust mites, or latex.

Also tell your doctor if you have:

Crotalidae antivenin is made from the blood or plasma of healthy horses or sheep. Animal blood or plasma may contain viruses and other infectious agents. Blood and plasma are tested and treated to reduce the risk of it containing infectious agents, but there is still a small possibility it could transmit disease. Talk with your doctor about the risks and benefits of using this medication.

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant.

It is not known whether Crotalidae antivenin passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

In an emergency situation it may not be possible to tell your caregivers if you are pregnant or breast-feeding. Make sure any doctor caring for your pregnancy or your baby knows you have received this medicine.

How is CroFab given?

Treatment with Crotalidae antivenin should be started as soon as possible after the first appearance of symptoms of a snake bite (fang marks in the skin with swelling or redness and pain, blurred vision, sweating, increased salivation, vomiting, uncontrolled bleeding, trouble breathing, weakness, loss of muscle control, or numbness in the face or body).

Crotalidae antivenin is injected into a vein through an IV. A healthcare provider will give you this injection. Crotalidae antivenin must be given slowly, and the IV infusion can take at least 60 minutes to complete.

CroFab is most effective if given within 6 hours after the snakebite occurred.

You will be watched closely for up to 60 minutes after receiving Crotalidae antivenin, to make sure this medicine is helping your condition.

You may need to receive additional doses if your condition does not improve after the first dose. Once your symptoms are under control, you may be given more doses every 6 hours for up to 18 hours or longer. Your doctor will determine how long to treat you with Crotalidae antivenin.

Venom from a snake bite can increase your risk of bleeding, which can be severe or life-threatening. Contact your doctor or seek emergency medical attention if you have any bleeding that will not stop.

Your doctor will need to check your progress for up to 2 weeks or longer after you are treated with Crotalidae antivenin. You may need to be re-treated with this medicine, or with other drugs that can help your blood to clot.

What happens if I miss a dose?

Because you will receive Crotalidae antivenin in a clinical setting, you are not likely to miss a dose.

What happens if I overdose?

Since CroFab is given by a healthcare professional in a medical setting, an overdose is unlikely to occur.

What should I avoid after receiving CroFab?

After a snakebite, you should avoid activities that may increase your risk of bleeding or injury. Use extra care to prevent bleeding while shaving or brushing your teeth.

CroFab side effects

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.

CroFab may cause serious side effects. 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 of CroFab 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.

What other drugs will affect CroFab?

Other drugs may interact with antivenin (Crotalidae) polyvalent, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

More about CroFab (antivenin (crotalidae) polyvalent)

Patient resources

Other brands

Anavip, Antivenin Polyvalent

Professional resources

Related treatment guides

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

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