Antivenin (Latrodectus Mactans)

Antivenin latrodectus mactans is a drug that is used to treat the bite of the black widow spider.

Overview

Antivenin latrodectus mactans is an antivenin drug that is used in the treatment of serious symptoms in patients who have been bitten by the black widow spider. The drug is an immunizing agent.

In the US, the medication is known under the brand name antivenin - spider. Black widow spider antivenin comes in injectable or powder for solution form. This drug should only be used by, or under the close supervision of, a doctor. Antivenin latrodectus mactans is administered intravenously.

Black widow spiders belong to the genus, Theridiidae. These highly aggressive spiders are found in most temperate regions around the world, including the south and western United States, southern Asia and Europe, Africa, Australia, and much of South America. Black widow spiders commonly invade homes, seeking out warm, dark spaces. Bites generally occur when someone accidentally touches the spider while reaching into a dark cupboard or crawl space.

The black widow is the most poisonous spider in North America, with venom that is reportedly 15 times more potent than that of a rattlesnake. The spider's venom is called alpha-latrotoxin and works by manipulating the body's nerve cells. The poison fuses itself with a nerve cell and forms pores in the membrane, allowing neurotransmitters to flood the cells, triggering uncontrollable muscle spasms. As the quantity of poison injected by the spider is very small, a healthy adult can usually process the toxins within a few hours and excrete them, and very few people actually die from a black widow spider bite.

Conditions treated

Type of medicine

  • Antivenin
  • Intravenous injection (vial)
  • Immunizing agent

Side effects

In addition to its desired effects, this medication can cause unwanted side effects in some people. Not all the side effects outlined below will occur, but you may need medical attention if you are affected. In the event that you do suffer any of the side effects mentioned, you should seek medical attention immediately.

Some patients who have been given this medication can suffer a serious allergic reaction called anaphylaxis. This condition is potentially fatal and should be treated as a medical emergency. Anaphylaxis causes irregular or very fast breathing, struggling for breath, wheezing, and loss of consciousness.

If you notice any of the following side effects, you should consult your doctor immediately:

  • problems with swallowing
  • cough
  • rapid heartbeat
  • dizzy spells
  • a general feeling of discomfort
  • fever
  • hives or a skin rash
  • joint inflammation
  • itchiness or reddening of the skin, particularly around the ears
  • muscle cramps or feeling 'achy'
  • swelling around the face, lips, tongue, eyes or the inside of the nose
  • breathing difficulties
  • swollen lymph glands
  • tightening across the chest
  • a sudden onset of fatigue or weakness

You may experience other strange or unusual effects not listed above when you have been treated with this medication. If you have any concerns, contact your doctor for advice.

Dosage

The correct dosage of this medication will vary between patients, depending on the extent of envenomation (i.e. number and depth of bites). The patient's age and body weight should also be taken into account when calculating the correct dose of this medication.

Antivenin latrodectus mactans should be given by slow IV infusion or intramuscular injection. In cases where the black widow spider envenomation is severe, the patient is under 12 years of age, or the patient is in shock, it is preferred to use the IV infusion method of administration.

One vial of antivenin is usually sufficient for both adults and children.

IM administration

A vial of powder should be diluted in 2.5ml of sterile diluent or 2.5ml of sterile water for injection. Shake the vial with the diluent needle still in situ in the rubber stopper, until the contents have dissolved completely. The preferred injection site is in the anterolateral thigh, so that a tourniquet can be applied if a serious allergic reaction occurs.

IV administration

A vial of powder should be diluted in 2.5ml of sterile diluent or 2.5ml of sterile water for injection. Shake the vial with the diluent needle still in situ in the rubber stopper, until the contents have dissolved completely. Dilute the reconstituted antivenin in 10ml to 50ml of sterile water and infuse the dose over 15 minutes.

Major drug interactions

Some medications should not be used together, as this may change how the drugs work and could also increase the risk of serious side-effects. However, in some cases, it may be appropriate to use two or more different medications, even though an interaction may occur. In this case, your doctor may opt to change the dose of one of your prescriptions. Alternatively, your doctor may suggest some precautions that you can take to negate the effect of any interactions.

There are no listings of any drugs that cause serious interactions with antivenin latrodectus mactans.

Warnings

The presence of any other medication conditions can sometimes affect the efficacy of antivenin latrodectus mactans. Be sure to tell your doctor if you have any other medication problems, before you receive this medication.

Patients with a history of allergy to horse serum should not be treated with this medication unless absolutely necessary. Some patients who are sensitive to horse serum can be at risk of developing anaphylaxis. Prior to intravenous administration a skin test should be carried out, interpreted, and the therapy modified if necessary.

Antivenin latrodectus mactans should be used with caution in patients with a history of asthma, as this medication may make the condition worse.

If you have received a dose of this medication and begin to feel feverish or uncomfortable, or if you develop a rash or itchy skin, you should tell your doctor immediately. In addition, you should seek medical advice if you begin to experience muscle aches, swollen lymph glands, or inflammation of the joints within eight to 12 days of receiving this drug.

There is no evidence that infants are at risk from this medication through breastfeeding. However, you should discuss this with your doctor and weigh the potential benefits against the risks of taking this medication if you are breastfeeding. This drug has not shown to be dangerous to unborn babies.

In some people, antivenin latrodectus mactans can cause anaphylaxis. This is a potentially fatal condition for which patients should always receive immediate medical attention. Symptoms of anaphylactic shock usually include accelerated and irregular breathing, struggling for breath, wheezing, and loss of consciousness. The patient may appear pale, the heartbeat may become extremely irregular or elevated, and large, flat swellings may appear around the eyelids or the eyes. If any of these side effects appear, you should summon emergency medical assistance straight away.

Storage

Refer to your doctor or pharmacist for specific use and storage instructions for this medication. If you live in an area where black widow spiders are common, it may be advisable to keep a small supply of antivenin latrodectus mactans in your home for use in an emergency.

Always keep this medication safely stored away from children or pets. If a pet does consume the drug, seek veterinary advice without delay.

Do not use any medicine that has passed its use-by date. Do not flush unused medication down the toilet or tip it down the drain. Do not discard unused medication in your trash can where it could be found and eaten by children or pets.

Summary

Antivenin latrodectus mactans is an antivenin drug that is used in the treatment of serious symptoms in patients who have been bitten by the black widow spider. The drug is an immunizing agent.

The most serious side effect of antivenin is anaphylaxis, and patients should receive a skin test for this before the drug is administered. This condition is potentially fatal and should be treated as a medical emergency. Anaphylaxis causes irregular or very fast breathing, struggling for breath, wheezing, and loss of consciousness.

Antivenin latrodectus mactans is highly effective in the treatment of black widow spider bites. However, there are other spiders that can resemble the black widow in appearance. To avoid confusion, it is important that the medical team attending the casualty are certain that the culprit was indeed a black widow. The black widow spider usually has a distinctive red cross-shape on its abdomen. The female of the species is larger than the male and her bite is usually more potent.

Black widow spiders are very aggressive when cornered. Do not try to catch or kill the spider as you could risk being bitten. If possible try to take a photograph of the spider or at least make an accurate description of it when reporting the incident to the emergency services. This will enable the emergency room to have the correct antivenin prepared before the casualty arrives, allowing immediate treatment and a much quicker resolution of the symptoms.

Resources
Last Reviewed:
December 22, 2017
Last Updated:
April 27, 2018