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Before administration, read "Precautions" and "Systemic Reactions" sections below. Since the possibility of a severe immediate reaction (anaphylaxis) exists whenever a horse-serum-containing product is administered, appropriate therapeutic agents, including a tourniquet, airway, oxygen, epinephrine, an injectable pressor amine, and corticosteroid, must be available and ready for immediate use. Constant attendance and observation of the patient for untoward reactions are mandatory when Antivenin is administered. Should any systemic reaction occur, administration should be discontinued immediately and appropriate treatment initiated.

The intravenous route of administration is preferred, and probably should always be used for moderate or severe envenomation. Intravenous administration is mandatory if venom-induced shock is present. To be most effective, Antivenin should be administered within 4 hours of the bite; it is less effective when given after 8 hours and may be of questionable value after 12 hours. However, it is recommended that Antivenin therapy be given in severe poisonings, even if 24 hours have elapsed since the time of the bite. It should be kept in mind that maximum blood levels of Antivenin may not be obtained for 8 or more hours after intramuscular administration.

For intravenous-drip use, prepare a 1:1 to 1:10 dilution of reconstituted Antivenin in Sodium Chloride Injection, USP, or 5% Dextrose Injection, USP. To avoid foaming, mix by gently swirling rather than shaking. Allow the initial 5 to 10 mL to infuse over a 3- to 5-minute period, with careful observation of the patient for evidence of untoward reaction. If no symptoms or signs of an immediate systemic reaction appear, continue the infusion with delivery at the maximum safe rate for intravenous fluid administration. The dilution of Antivenin to be used, the type of electrolyte solution used for dilution, and the rate of intravenous delivery of the diluted Antivenin must take into consideration the age, weight, and cardiac status of the patient; the severity of envenomation; the total amount and type of parenteral fluids it is anticipated will be given or are needed; and the interval between bite and initiation of specific therapy.

It is important to give as soon as possible the entire initial dose of Antivenin as based on the best estimate of the severity of envenomation at the time treatment is begun. The following initial doses are recommended:^3,4,8 no envenomation-none.

minimal envenomation-20-40 mL (contents of 2 to 4 vials).

moderate envenomation-50-90 mL (contents of 5 to 9 vials).

severe envenomation-100-150 mL or more (contents of 10 to 15 or more vials).

These recommended initial-dosage volumes are in general accord with those of others.

The need for additional Antivenin must be based on the clinical response to the initial dose and continuing assessment of the severity of poisoning. If swelling continues to progress or if systemic symptoms or signs of envenomation increase in severity or if new manifestations appear, for example, fall in hematocrit or hypotension, administer an additional 10 to 50 mL (contents of 1 to 5 vials) intravenously.

Envenomation by large snakes in children or small adults requires larger doses of Antivenin. The amount administered to a child is not based on weight.

If Antivenin is given intramuscularly, it should be given into a large muscle mass, preferably the gluteal area, with care to avoid nerve trunks. Antivenin should never be injected into a finger or toe.

The effectiveness of corticosteroids in treatment of envenomation per se or venom shock is not resolved. Russell³ and others believe corticosteraids may mask the seriousness of hypovolemia in moderate or severe poisoning and have little, if any, effect on the local-tissue response to rattler venoms. Corticosteroids should not be given simultaneously with Antivenin on a routine basis or during the acute state of envenomation; however, their use may be necessary to treat immediate allergic reactions to Antivenin, and corticosteroids are the agents of choice for treating serious delayed reactions to Antivenin.

Snakes' mouths do not harbor Clostridium tetani. However, appropriate tetanus prophylaxis is indicated, since tetanus spores may be carried into the fang puncture wounds by dirt present on skin at time of bite or by nonsterile first-aid procedures.

A broad-spectrum antibiotic in adequate dosage is indicated if local tissue damage is evident.

Shock following envenomation is treated like shock resulting from hypovolemia from any cause, including administration of whole blood, plasma, albumin, or other plasma expanders, as indicated.

Aspirin or codeine is usually adequate for relieving pain. Sedation with phenobarbital or mild tranquilizers may be used if indicated, but not in the presence of respiratory failure.

The bitten extremity should not be packed in ice, and so-called "cryotherapy" is contraindicated.

Compartment syndromes may complicate pit viper envenomations, especially those caused by bites on the lower extremities. Prompt surgical consultation is indicated whenever a closed-compartment syndrome is suspected.

Defibrination and disseminated intravascular coagulation (DIC) syndromes have been associated with envenomation caused by some pit vipers native to the United States, and appropriate therapy may be indicated.

Technic for Reconstituting the Dried Antivenin

Pry off the small metal disc in the cap over the diaphragms of the vials of Antivenin and diluent. Swab the exposed surface of the rubber diaphragms of both vials with an appropriate germicide. With a sterile 10 mL syringe and needle, withdraw the diluent (Bacteriostatic Water for Injection, USP, containing phenylmercuric nitrate 1:100,000) from the vial of diluent and inject it into the vial of Antivenin. Gentle agitation will hasten complete dissolution of the lyophilized Antivenin.

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