Some commonly used names are: antivenin(crotalidae)polyvalent; antvenin crotalid serum.Available as a generic name product in the U.S. and Canada.

• Immunizing agent, passive

Pit viper antivenin belongs to a group of medicines known as immunizing agents. It is used to treat the bites of certain poisonous snakes called pit vipers (crotalids), which are native to Central, North, and South America. Pit vipers include rattlesnakes, such as the Eastern and the Western diamond rattlesnakes; copperheads and cottonmouth moccasins, including those of Korea and Japan; the fer-de-lance and similar species; the tropical rattler (Cascabel) and similar species; the Cantil; and the bushmaster of Central and South America.

Pit viper antivenin is to be used only by or under the supervision of a doctor. It is available in the following dosage form:

Parenteral
• Injection (U.S. and Canada)

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 pit viper antivenin, the following should be considered:

Allergies—Tell your doctor if you have ever been bitten by a poisonous snake before and if you have ever had an unusual or allergic reaction to pit viper antivenin, to horses, or to any products of horse origin, such as horse serum. Also tell your health care professional if you are allergic to any other substances, such as preservatives. Before giving you this medicine, your doctor will do a skin test to see whether you are at risk of having a serious reaction to pit viper antivenin or to horse serum (contained in this medicine).

Diet—Make certain your health care professional knows if you are on any special diet, such as a low-sodium or low-sugar diet.

Pregnancy—Studies on effects in pregnancy have not been done in either humans or animals. However, poisoning by pit vipers may result in miscarriages.

Breast-feeding—It is not known whether pit viper antivenin passes into the breast milk. However, pit viper antivenin has not been reported to cause problems in nursing babies.

Children—Studies show that children tolerate pit viper antivenin better than do adults. However, children usually have more severe reactions to snakebite poisoning because of the greater amount of poison per body weight. Therefore, children may need larger doses of pit viper antivenin than do adults.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults. Although there is no specific information comparing use of pit viper antivenin in the elderly with use in other age groups, this medicine is not expected to cause different side effects or problems in older people than it does in younger adults.

Dosing—

The dose of pit viper antivenin will be different for different patients. The dose you receive will depend on your body's reaction to the skin test, your reaction to the treatment itself, and the severity of the poisoning. However, the dose does not depend on your body weight.

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 immediately if any of the following side effects occur:

• More common
  • Difficulty in breathing or swallowing;  hives;  itching, especially of feet or hands;  reddening of skin, especially around ears;  swelling of eyes, face, or inside of nose;  unusual tiredness or weakness (sudden and severe) 
  
  

For up to 24 days after you have received pit viper antivenin, you may develop symptoms of a side effect called serum sickness. The severity of the symptoms and the length of the sickness depend on the amount of pit viper antivenin you were given and how long the treatment lasted. During the 24 days after treatment with pit viper antivenin, check with your doctor if you notice any of the following side effects:

• Fever;  joint pain;  rash and itching;  swollen lymph glands 

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