Rattle Snake Envenomation Medication

The only proven therapy for snakebites is antivenom.^[26] The physician also must be prepared to support the victim's cardiovascular and respiratory systems.^[27]

Class Summary

This agent neutralizes toxins from snakebites. Two antivenoms are available: CroFab and Antivenin Crotalidae Polyvalent. CroFab has been available since December 2000. CroFab is manufactured by Protherics Inc, Nashville, Tennessee and distributed by Fougera, Melville, New York (800-231-0206). Antivenin Crotalidae Polyvalent, manufactured by Wyeth-Ayerst, is still available on the shelves of many hospital pharmacies but is no longer being produced. Whether the production of Antivenin will resume is unknown. Meanwhile, another antivenom (Antivipmyn, manufactured by Instituto Bioclon S.A. de C.V.) has been FDA approved for experimental use and is currently undergoing phase III clinical trials.

CroFab

CroFab (Crotalidae Polyvalent Immune Fab Ovine) appears to be more specific against rattlesnake venom and less allergenic than Antivenin Crotalidae Polyvalent. The usual starting dose is 4-6 vials. Reconstitute each vial with 10 mL of sterile water for USP injection and mix by continuous swirling. Once CroFab goes into solution, dilute the vials further into total volume of 250 mL of NS. Start infusion slowly at rate of 50 mL/h for first 10 min. During initial infusion, observe patient for allergic reaction. If no reaction occurs, may increase infusion rate to 250 mL/h until completion. Observe patient for up to 1 h after completion to determine if initial control of envenomation achieved, as defined by arrest of progression of any and all components of envenomation syndrome (ie, no further advancement of swelling, improvement of systemic effects, and improving coagulopathy).

Crotalidae polyvalent antivenom (equine)

Manufactured by Wyeth-Ayerst. To mix antivenom, dissolve in 10 mL warm saline by gentle agitation. May take anywhere from 20-90 min or more to dissolve. Further dilute it 1:2 or 1:4 or more (eg, mix 10 dissolved vials into a total dilution of 200 cm³). Start infusion at 1 mL/min for 10 min, closely monitoring for signs of allergic reaction. If no allergic reaction occurs, increase rate to complete infusion over 1 h. For children, run infusion at 10 mL/kg/h. Diluting antivenom in greater volume of fluid and infusing slowly may reduce occurrence acute adverse reactions.

Routine premedication with antihistamines (H1 and H2 blockers) recommended. Pretreatment with epinephrine (1:1000) 0.25 mL SC was shown to reduce acute adverse reactions to antivenom in one series, although risks of epinephrine should be considered. Pretreatment with steroids is unlikely to prevent immediate reactions but may be helpful later if continued antivenom indicated despite allergic reaction.

Class Summary

These agents are used for treatment of acute allergic reactions to antivenom or venom (not for treatment of envenomation).

Diphenhydramine (Benadryl)

Used for the symptomatic relief of allergic symptoms caused by histamine released in response to allergens

Class Summary

Patients should be immunized against tetanus.

Diphtheria-tetanus toxoid (dT)

Used to induce active immunity against tetanus in selected patients. Tetanus and diphtheria toxoids are the immunizing agents of choice for most adults and children >7 y. Booster doses are necessary to maintain tetanus immunity throughout life because tetanus spores are ubiquitous.

Pregnant patients should receive only tetanus toxoid, not diphtheria antigen–containing product. In children and adults, may administer into deltoid or midlateral thigh muscles. In infants, preferred site of administration is mid-thigh laterally.

Class Summary

Prophylactic antibiotics are not routinely indicated. However, wound infections should be treated with antibiotics. Common etiologic bacteria in wound infections include Pseudomonas aeruginosa, Staphylococcus epidermidis, Enterobacteriaceae species, and Clostridium species. For infected wounds, empiric therapy may include ciprofloxacin (contraindicated in pediatric patients and pregnant women) as a single agent or a combination of ceftriaxone plus amoxicillin-clavulanate, pending wound culture and sensitivity results. Retained foreign bodies (eg, a fang, other tooth) are a common cause of wound infection.

Ceftriaxone (Rocephin)

Third-generation cephalosporin with broad-spectrum gram-negative activity; lower efficacy against gram-positive organisms; higher efficacy against resistant organisms. Arrests bacterial growth by binding to one or more penicillin-binding proteins.

Class Summary

Pain control is essential to quality patient care. It ensures patient comfort and promotes pulmonary toilet. Most analgesics have sedating properties, which are beneficial for patients who have sustained painful snakebites. Opioid analgesics are recommended for pain control as needed. NSAIDs may contribute to coagulopathies.

Morphine sulfate (Astramorph, Duramorph, and MS Contin)

DOC for narcotic analgesia because of its reliable and predictable effects, safety profile, and ease of reversibility with naloxone.

Morphine sulfate administered IV may be dosed in a number of ways and commonly is titrated until the desired effect is obtained.

Class Summary

Consider transfusion if antivenom does not correct coagulopathy or if imminent risk of serious bleeding. Transfusion is generally recommended for life-threatening bleeding (rare), platelets < 20,000 mm³, or hemoglobin < 7 g/dL. Transfusion should be utilized after antivenom as a temporizing or adjuvant measure because antivenom may correct coagulopathies more definitively (although this is an area with particularly contradictory literature). Coagulopathy often recurs and may persist for 2 weeks or more after envenomation.

Platelets, fresh frozen plasma (FFP), and packed RBCs

Used preferentially to whole blood because they limit volume, immune, and storage complications. PRBCs have 80% less plasma, are less immunogenic, and can be stored about 40 d (versus 35 d for whole blood). PRBCs are obtained after centrifugation of whole blood. Leukocyte-poor PRBCs are used in patients who are transplant candidates/recipients or in those with prior febrile transfusion reactions. Washed or frozen PRBCs are used in individuals with hypersensitivity transfusion reactions. Blood can be administered over 3-4 hours, premedicating with acetaminophen and diphenhydramine to prevent febrile transfusion reactions.