Antivenin (Crotalidae Polyvalent Immune Fab)

When an individual is bitten by a poisonous snake, such as a rattlesnake or a water moccasin, a strong anti-venom treatment, such as Antivenin, is required.


Antivenin is used to treat snakebite victims, where the bite transmits a natural toxin to the victim. As an anti-venom serum, this drug alleviates the effects of the venom and can return the victim back to a healthy state. As with any poisoning, timing is essential and the bite victim should be given immediate medical attention to ensure an effective treatment. Antivenin should be administered by healthcare professionals via an IV injection.

Conditioms treated

  • Snake bites

Type of Medicine

  • Anti-venom

Side Effects

Antivenin may cause some adverse side effects in rare cases. While not every patient who receives this anti-venom will interact negatively, the presentation of these side effects should be immediately reported to the patient's doctor. Among the most common adverse reactions, patients have developed inhibited mobility. In some cases, the inability to move was accompanied by a swelling or bloating of the face, arms, hands, lower legs, and feet. If the patient experiences this, he or she should return to their doctor immediately for treatment.

Additionally, common side effects may include a reddening or flushing of the skin. Similarly, the patient can also cause an itching rash. If this occurs, the patient should refrain from scratching until medical attention can be sought.

Muscle and joint pain or stiffness may also be experienced by some patients, while taking Antivenin. Nausea, vomiting, unexplained and unusual weight changes, very warm skin, and tingling hands and feet may also be a part of the anti-venom's effects on the patient.

Less commonly reported, but other possible side effects, include black or tarry stools, bleeding gums, and blood in urine or stools. Additionally, dizziness, confusion, chills, and a decreased ability to urinate may also present an adverse reaction to the treatment. Some patients experienced a fever with fainting spells and a general feeling of lightheadedness. A dry mouth, quickened heart rate, and rapid breathing are other possible side effects. Also rare but possible are small red spots on the skin, along with noticeably sunken eyes and excessive thirst.

Patients should also be aware of an overall feeling of weakness, general fatigue, and the appearance of wrinkled skin. The presence of these side effects or any others should be reported to the patient's doctor as soon as possible.

Other side effects have been reported, but have been so minimal that treatment for them was not necessary. In such cases, patients also reported that the symptoms went away, as their bodies adjusted to the anti-venom medication. Patients who are especially concerned about the side effects should discuss the matter with their healthcare provider. The patient's doctor may have treatments or may suggest lifestyle changes that can minimize or eliminate the side effects. While Antivenin treatment may be the best option, that doesn't mean the patient must endure adverse reactions without relief. Communication is key to a positive recovery experience.


Antivenin dosage is the same for adults and children. The initial dose should consist of four to six vials administered intravenously within a 60-minute time frame. The rate of infusion should be set to 25 to 50 mL/hour for the first 10 minutes. If the patient doesn't show any signs of an allergic reaction, dosage can be increased to 250 mL per hour.

Antivenin should be continued at this rate for 60 minutes every six hours for a maximum of up to 18 hours. By this time, Antivenin should have established a measure of control over the poison in the patient's system.

A maintenance dose of two vials should then be administered to the patient every six hours for up to 18 hours, making a total of three doses. Depending on the patient's response to the course of treatment, his doctor may prescribe an additional two vials.


As with any drug treatment, it's important that the patient informs the doctor about any and all medications they're currently taking. In addition to prescription drugs, this includes over the counter drugs, vitamins and herbal supplements, and recreational drugs that could be in the patient's system. This will help the doctor determine how the patient will react to the Antivenin drug therapy.

In cases of snake bites, the patient may not always be conscious or lucid enough to supply this information. Where this is the case, the patient should be encouraged to give this information to his attending healthcare provider as soon as he's well enough to do so. This will still assist the doctor in establishing the best course of treatment for the patient.

Severe interactions specific to Antivenin have been documented where the patient was receiving beta-adrenergic blockers, such as cardioselective agents. In such circumstances, a condition of anaphylaxis was produced. The treatment of Anaphylaxis can be especially problematic under these conditions, because beta-adrenergic blockers can make anaphylaxis resistant to treatment.

Other drugs known to interact with Antivenin:

  • acebutolol
  • atenolol
  • atenolol / chlorthalidone
  • bendroflumethiazide / nadolol
  • betaxolol
  • betaxolol ophthalmic
  • bisoprolol
  • bisoprolol / hydrochlorothiazide
  • brimonidine / timolol ophthalmic
  • carteolol
  • carteolol ophthalmic
  • carvedilol
  • dorzolamide / timolol ophthalmic
  • esmolol
  • hydrochlorothiazide / metoprolol
  • hydrochlorothiazide / propranolol
  • hydrochlorothiazide / timolol
  • labetalol
  • levobetaxolol ophthalmic
  • levobunolol ophthalmic
  • metipranolol ophthalmic
  • metoprolol
  • nadolol
  • nebivolol
  • nebivolol / valsartan
  • penbutolol
  • pindolol
  • propranolol
  • sotalol
  • timolol
  • timolol ophthalmic


In addition to sharing any drug information with his doctor, the patient should also share whether or not they are allergic to any animals. Antivenin is derived from equine/horse immune globulin F(ab')2, so animal allergy information is especially important to divulge. Anaphylaxis and anaphylactoid reactions have been caused by administering the treatment to patients with allergies.

Additionally, patients who have previously been treated for snake bites with Crotalidae immune F(ab')2 or another equine-derived antivenom/antitoxin may be at a greater risk of heightened sensitivity to Antivenin. They may experience a hypersensitivity reaction that will lead to anaphylaxis. If so, the doctor is advised to stop administering the drug immediately and begin emergency treatment for anaphylaxis. Care for an anaphylactic reaction includes epinephrine 1 mg/mL, corticosteroids, or diphenhydramine.

The patient may also experience delayed serum sickness, following the completion of Antivenin treatment. The possibility of delayed serum sickness exists anytime from the time the final dose is administered to up to two weeks. Routine follow up visits should help the doctor monitor the patient for signs of delayed serum sickness until the recovery period has run its course. Symptoms of delayed serum sickness include:

  • fever
  • arthralgia
  • myalgia
  • urticaria
  • rash
  • pruritus

The manufacturing of the serum can result in Antivenin containing small amounts of Cresol. Allergic reactions, including muscle pain, can result.

Doctors should also be aware that Antivenin is produced from horse plasma. As such, the serum may contain infectious agents and viruses. The possibility of transmitting a disease to the patient is minimal, but it is present.

There is no cause to suspect Antivenin poses a risk to pregnant women. However, doctors are urged to evaluate the mother's overall health and prognosis, when determining to prescribe the anti-venom drug therapy. The primary concern is in treating the poisoning produced by the snake bite. While great care should be taken in monitoring the baby's response, the mother's return to health should be the focus of treatment.

An allergic reaction may occur when using Antivenin. Symptoms include itching and red hives, trouble breathing, swelling (face, lips, tongue, and/or throat), and lightheadedness. If the patient experiences any of these symptoms, Antivenin treatment should be immediately stopped and emergency care implemented.

The attending doctor should also be informed of medical conditions currently experienced by the patient. In particular, cancer, congestive heart failure and an overactive thyroid could present complications, when Antivenin is administered. The doctor should also be aware of certain blood problems. Issues with excessive bleeding or with blood clotting, such as hemophilia, should be reported immediately, so the physician can closely monitor the patient's condition.


Antivenin can be stored at room temperature, but the temperature should not exceed 25 ºC (77ºF). For brief periods, the serum may be exposed to temperatures as high as 40ºC (104ºF), but only rarely and only when absolutely necessary. Care should be taken to not allow the drug to freeze. Partially used vials are unusable for future doses and should be immediately discarded.

Antivenin can be reconstituted by swirling one vial of the solution with 10 mL of sterile saline. Once properly mixed, the serum should appear yellow/green in color and should be opalescent. The solution cannot be reused, if it's discolored, or if it appears cloudy or opaque.

People are rarely prepared for a snake bite and, to be fair, such an occurrence is rare enough that most people may never suffer from venom poisoning. When it does happen, getting the victim to a treatment facility is vital. The administering of an Antivenin course of drug therapy can help rid the victim's body of toxins, but treatment must be started in a timely manner. In addition to informing the doctor of the source of the bite, the patient, or the patient's loved ones, should supply as much information as possible. By giving the physician the patient's drug history and a list of allergies, an adverse reaction may be avoided.

Last Reviewed:
December 24, 2017
Last Updated:
April 02, 2018
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