Drug Information for Wyeth Antivenin (Micrurus fulvius) (Equine Origin) North American Coral Snake Antivenin (Wyeth Pharmaceuticals Company): INDICATION

  • Antivenin (Micrurus fulvius) (equine origin) is indicated only for the treatment of envenomation caused by bites of those coral snakes specified in the following paragraph.

  • Coral Snakes and Bites

  • Two genera of coral snakes are found in the United States—Micrurus (including the eastern and Texas varieties) and Micruroides (the Sonoran or Arizona variety), found only in southeastern Arizona and southwestern New Mexico.

    There are two subspecies of Micrurus fulvius native to the United States: 1) M.f. fulvius, found in the area from eastern North Carolina through the tip of Florida and in the Gulf coastal plain to the Mississippi River; 2) M.f. tenere, the Texas coral snake, found west of the Mississippi River in Louisiana, Arkansas, and Texas. These subspecies can be differentiated by experts but are very similar in appearance. The adult coral snake (M. fulvius) may vary between 20 to 44 inches in length, has a black snout, and yellow, black, and red bands encircling the body. The red and black rings are wider than the INTERPOSED yellow rings. However, melanistic (all black), albino (all white), and partially pigmented forms may be rarely seen. In contrast to the pit vipers (rattlesnakes, copperheads, cottonmouths), coral snakes have round pupils and lack facial pits. They are secretive and rarely bite unless disturbed or HANDLED. The fangs are short, erect, and fixed to the maxilla. Venom flows through the fang from a duct at its base. Pit vipers usually strike and then rapidly withdraw the head after insertion of the fangs. However, coral snakes, with their less efficient biting mechanism, may strike, hold on, and “chew”, presumably so a sufficient amount of venom can be introduced to immobilize the prey. This “chewing” action may result in more than one “bite”, and the victim MAY recall the colorful snake “hanging on” for a “minute” or so. Permitted to bite under laboratory conditions, M.f. fulvius have yielded 1 to 28 mg of venom.1,2 Fix and Minton,2 after measuring the venom yields of 14 M.f. fulvius and the length of the individual snakes, found a positive linear relationship; six snakes measuring between 29 and 44 inches in length yielded 14 to 28 mg of dried venom, whereas eight measuring 21 to 28 inches in length yielded 2 to 10 mg. The adult human LD100 of M.f. fulvius venom has been estimated to be 4 to 5 mg of dried venom. Coral snake venom is chiefly paralytic (neurotoxic) in action, and usually only minimal-to-moderate tissue reaction and pain occur at the site of bite. Most coral snakebites are inflicted upon the upper extremities, especially the hands and fingers. The limited size of the biting apparatus makes it difficult for the coral snake to penetrate clothing or to successfully grasp any part of the body except the hands and feet. Hence, in areas where coral snakes are found, adherence to the simple practices of NEVER picking up colorful snakes, NEVER putting the hands where they cannot be seen (reaching behind rocks, logs, flowers, etc.), and always wearing leather shoes would substantially reduce the chances of a bite.

    There are few published reports describing envenomation caused by coral snakebites.1,3-7 It has been estimated that only 20±5 coral snakebites occur in the United States each year.3 Although those persons who exhibit one or more fang punctures seem most likely to develop envenomation, there is NO way to predict which victim may be envenomated by a coral snakebite. Even a reliable observation that the biting snake did or did not "hang on" should NOT be used to predict the likelihood or possible severity of envenomation. Coral snakebites, like bites by crotalids, are not always followed by envenomation. However, in contradistinction to crotalid bites, in which moderate-to-severe envenomation usually can be predicted by rapid onset of the local effects (e.g., pain, discoloration, edema), severe and even fatal envenomation from a coral snakebite can be present without any significant local tissue reaction.

    Systemic signs and symptoms of envenomation usually begin from one to seven hours after the bite but may be delayed for as long as 18 hours. If envenomation occurs, the symptoms and signs may progress rapidly and precipitously. Paralysis has been observed within 2-1/2 hours post bite and appears to be of a bulbar type, involving cranial motor nerves. Death from respiratory paralysis has occurred within four hours of the accident.

    SYSTEMIC signs and symptoms of envenomation may include euphoria, lethargy, weakness, nausea, vomiting, excessive salivation, ptosis of the eyelids, dyspnea, abnormal reflexes, convulsions, and motor weakness or paralysis, including complete respiratory paralysis. LOCAL signs and symptoms may include scratch marks or fang puncture wounds, no-to-moderate edema, erythema, pain at the bite site, and paresthesia in the bitten extremity.

    TREATMENT OF CORAL SNAKEBITE: If practical, immobilize victim immediately and completely. Carry the victim to the nearest hospital as soon as possible. If complete immobilization is not practical, splint the bitten extremity to limit spread of venom. If the biting snake was killed, bring it to the hospital also.

    ANY victim of a bite by a coral snake with ANY evidence of a break in the skin caused by the snake’s teeth or fangs should be HOSPITALIZED for observation and/or treatment. Cleanse the bite area with germicidal soap and water to remove any venom remaining on the skin. If fang puncture wounds are present, application of a tourniquet and incision and suction over the fang punctures has been recommended,1,3 even though there is no evidence to indicate that incision and suction are or are not of value in removing coral snake venom. In addition to maintaining close observation of the patient for 24 hours, which should include checking the respiratory rate every 30 minutes, make sure the following will be available and ready for immediate use should need arise:

    - a supply of Antivenin (Micrurus fulvius)

    - an oxygen supply

    - a mechanical respirator

    - facilities and equipment for a tracheostomy

    - the services of an anesthesiologist

    Appropriate horse-serum sensitivity tests should be done so that, in case administration of Antivenin is subsequently required, a decision on how to proceed will have been made. Parrish and Khan3 have recommended intravenous administration of coral snake antivenin to patients with one or more fang puncture wounds as soon as possible and before onset of symptoms and signs of envenomation.

    If symptoms or signs of envenomation occur in a patient under observation or are already present at the time the patient is first seen, give Antivenin (Micrurus fulvius) promptly by the intravenous route. With vigorous treatment and careful observation, patients with complete respiratory paralysis have recovered, indicating that the respiratory paralysis is reversible.4,5 Hemoglobinuria has been observed in experimental animals envenomated by coral snakes. Hence, continuous bladder drainage is recommended with careful attention to urinary output and blood electrolyte balance.

    Appropriate tetanus prophylaxis is indicated as for any other potentially contaminated puncture wound.

  • Drug Information Provided by National Library of Medicine (NLM).