Why UpToDate? Product Editorial Subscription Options Subscribe Sign in. Learn how UpToDate can help you. Select the option that best describes you. View Topic. Font Size Small Normal Large.

Snakebites worldwide: Management. Formulary drug information for this topic. No drug references linked in this topic. Find in topic Formulary Print Share. View in. Language Chinese English.

Author: Julian White, AM, MB, BS, MD, FACTM Section Editors: Daniel F Danzl, MD Michelle Ruha, MD Deputy Editor: Michael Ganetsky, MD Literature review current through: Jan This topic last updated: Jan 11, Venomous snakes are widely distributed around the world and clinical effects from envenomation can overlap to a great degree even among different families of snakes.

This topic will discuss the management of snakebites that occur worldwide, other than those by snakes found in the United States. FIRST AID Initial first aid of snake envenomation is directed at reducing the spread of venom and expediting transfer to an appropriate medical center.

Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press. This content does not have an English version.

This content does not have an Arabic version. Appointments at Mayo Clinic Mayo Clinic offers appointments in Arizona, Florida and Minnesota and at Mayo Clinic Health System locations.

Request Appointment. First aid Snakebites: First aid. Sections Basics Multimedia. Products and services. Show references Snakebites. Merck Manual Professional Version. Accessed March 28, Elsevier Point of Care. Clinical Overview: Snake bites. Ruha M, eds.

Bites by Crotalinae snakes rattlesnakes, water moccasins [cottonmouths], or copperheads in the United States: Management. Venomous snakes. Centers for Disease Control and Prevention.

Hoecker JL expert opinion. Mayo Clinic. May 5, See also Mayo Clinic Minute: Rattlesnakes, scorpions and other desert dangers. Mayo Clinic Press Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press.

Mayo Clinic on Incontinence - Mayo Clinic Press Mayo Clinic on Incontinence The Essential Diabetes Book - Mayo Clinic Press The Essential Diabetes Book Mayo Clinic on Hearing and Balance - Mayo Clinic Press Mayo Clinic on Hearing and Balance FREE Mayo Clinic Diet Assessment - Mayo Clinic Press FREE Mayo Clinic Diet Assessment Mayo Clinic Health Letter - FREE book - Mayo Clinic Press Mayo Clinic Health Letter - FREE book.

If resumption of antivenom therapy is chosen, then the patient should receive pretreatment to blunt the allergic response eg, IV diphenhydramine 1. If signs or symptoms of anaphylaxis or hypersensitivity reactions occur again, antivenom administration should be discontinued immediately, appropriate therapy instituted, and the need for further antivenom treatment re-evaluated.

Assessment of response and need for redosing — The response to antivenom determines whether or not further doses are required table 1. Control of envenomation is indicated by all of the following [ 34 ]:.

Studies should include a complete blood count, prothrombin time PT , international normalized ratio INR , and fibrinogen. Patients who do not achieve control of envenomation after the initial dose of antivenom warrant repeat dosing under the guidance of a medical toxicologist or physician with similar expertise managing Crotalinae snakebites.

Prevention of early recurrent toxicity — Crotalidae Polyvalent-immune Fab ovine , brand name CroFab FabAV , and Crotalidae Immune F ab' 2 equine , brand name Anavip Fab2AV , the antivenoms available for Crotalinae snakebites in North America, differ in their rates of early recurrence and duration of effect see 'Efficacy' below.

Thus, the approach to preventing early recurrent toxicity depends upon the antivenom used:. Alternatively, if medical toxicology oversight and resources allow, the clinician may choose to perform careful clinical assessment of the bite site and measurement of coagulation studies every six hours to determine the need for additional antivenom [ 35 ].

Provision of scheduled maintenance doses of FabAV after initial control is achieved may limit recurrence of local venom effects and decrease rates of late hemotoxicity [ 21,26 ]. Yet even with use of maintenance doses, late hemotoxicity is reported in approximately 30 percent of patients [ 22,25,36 ].

Some experts suggest that in settings where close monitoring of local swelling and coagulation parameters can occur, as-needed dosing of FabAV antivenom may be more appropriate than scheduled dosing.

For example, in a retrospective observational study of adults that compared hospital length of stay and total vials used between patients treated with an as-needed versus a scheduled maintenance antivenom regimen, the as-needed group received fewer vials overall 8 versus 16 vials and had a shorter hospital length of stay 27 versus 34 hours [ 35 ].

Follow-up information was available for over 90 percent of patients in this study, and there were no differences in hospital readmissions, retreatment with antivenom, bleeding, or procedures between groups. However, patients were admitted to a toxicology service managed by full-time toxicology faculty practicing at the bedside and covered by hour onsite medical toxicology fellows.

The immediate availability of physicians with a high level of snakebite expertise likely optimized timely detection of local recurrence and hastened administration of antivenom when necessary.

From a practical standpoint, this degree of monitoring is not available at most hospitals where snakebite victims are managed. In those settings, a delay in recognition of and response to recurrence of local venom effects could result in increased local tissue injury, and scheduled maintenance dosing of FabAV is preferred.

However, patients should be observed for an additional 18 hours for re-emergence of local or hematologic effects. If these occur, additional doses of antivenom are indicated [ 26 ]. Identification and treatment of late hemotoxicity. Risk of late hemotoxicity — Among patients with rattlesnake envenomation who receive FabAV, the risk of late hemotoxicity is approximately 30 percent depending upon the geographic region and snake species involved [ 22,25,36 ].

Late hemotoxicity appears to be much less common in patients treated with Fab2AV. In a randomized clinical trial of patients receiving antivenom for a Crotalinae snakebite, 8 percent of patients who received Fab2AV experienced late hemotoxicity compared with 30 percent in the FabAV group [ 25 ].

Subsequent small observational studies from New Mexico and Arizona have revealed even lower rates of late hemotoxicity with use of Fab2AV 0 to 5 percent [ 29,37 ]. Recurrent and delayed hemotoxicity may become apparent as early as 24 hours after treatment with FabAV but can develop up to 14 days after initial control with antivenom [ 25 ].

This risk is increased in patients with abnormal platelets or fibrinogen within the first 12 hours after FabAV administration [ 38 ]. Risk may also be increased in patients with normal platelets and fibrinogen but who exhibit an elevated D-dimer or fibrin split products [ 39 ].

However, late, new-onset hematologic abnormalities may develop even without these indicators, likely due to early administration of antivenom to treat swelling, and prevention of onset of hemotoxicity with this treatment [ 40 ].

Monitoring — Since late hemotoxicity can develop following use of FabAV or Fab2AV, and risk cannot be predicted, all patients who receive antivenom warrant monitoring physical assessment and laboratory studies for late thrombocytopenia or hypofibrinogenemia according to the antivenom received [ 19 ] see 'Prevention of early recurrent toxicity' above :.

If any abnormal trends are noted, further laboratory monitoring is indicated. Additionally, patients with additional risk factors for bleeding may require early or more frequent assessments. Treatment — For patients in whom late hemotoxicity is identified, further management is determined based on the specific laboratory values, signs of bleeding, or presence of risk factors for serious bleeding [ 17, ].

Retreatment should be performed in consultation with a medical toxicologist or other physician with expertise in managing Crotalinae snakebites. An initial bolus dose of two vials of FabAV or four vials of Fab2AV is a reasonable starting point, with additional doses titrated to the neutralization of ongoing venom effects [ 38 ].

In some instances, total reversal of hemotoxicity with FabAV is not possible. In patients who have no significant bleeding, the clinician may choose improvement in coagulation parameters towards normal as an acceptable outcome [ 21 ].

Based on limited evidence, Fab2AV may be a more effective treatment for late hemotoxicity that occurs following use of FabAV [ 44 ]. Isolated late hypofibrinogenemia may be observed in healthy, nonpregnant patients without other risk factors for bleeding. These patients should be monitored for resolution of coagulation abnormalities, should not use medications that inhibit platelets, and should not undergo any surgical procedures or engage in activities that risk injury until hemotoxicity is resolved.

Complete resolution may take up to three weeks from the time of envenomation [ ]. Efficacy — Crotalidae Polyvalent-immune Fab ovine , brand name CroFab FabAV ; and Crotalidae Immune F ab' 2 equine , brand name Anavip Fab2AV are the two antivenoms available for bites by Crotalinae snakes in North America:.

When infused, these Fab fragments bind venom in the intravascular space and are renally excreted. The larger volume of distribution, compared with IgG and Fab2AV, results in more rapid decline in circulating antivenom levels.

Because approximately 50 percent of patients in the first phase of the clinical trial developed recurrence of local venom effects, routine maintenance doses in the first 18 hours are recommended for control of local effects. The half-life of FabAV is approximately 15 hours and shorter than Crotalinae venom substances, which may be detected for more than two weeks post-envenomation.

Thus, recurrence or delayed onset of hemotoxicity is possible in the days to weeks following treatment as antivenom levels decline and may necessitate repeated antivenom administration. When infused, these F ab' 2 fragments bind venom in the intravascular space. Because of the smaller volume of distribution compared with FabAV, circulating antivenom concentrations do not decline as rapidly, and routine maintenance doses in the first 18 hours following initial control are not required.

Although no studies have specifically looked at the effectiveness of Fab2AV and time to treatment, it had similar effectiveness to FabAV when given in the same timeframe [ 25 ].

Because the molecular weight of Fab2AV is above the threshold for renal clearance, these fragments are not cleared renally and have a longer half-life hours than FabAV [ 26 ]. Thus, recurrent hematologic toxicities occur at a lower rate than with FabAV [ 25 ].

Based upon small trials and observational studies, the majority of envenomated patients achieve control of toxicity local swelling and systemic effects after initial administration of one or two loading doses of either FabAV or Fab2AV, with some patients requiring additional doses [ ,23,25,29,37,47,48 ].

There is an approximately 2 to 3 percent risk of adverse immune reactions or type 1 acute and type 3 delayed, "serum sickness" hypersensitivity; these are typically minor [ 25 ].

Fab2AV appears to have similar initial therapeutic benefit compared with FabAV. For example, in a trial of over children and adults with Crotalinae envenomation, Fab2AV was found to have comparable efficacy as FabAV in terms of initial control of hemotoxicity after rattlesnake envenomation.

Individuals receiving Fab2AV also did not require maintenance dosing for continued control of local envenomation effects, had a lower incidence of late hemotoxicity 5 to 10 percent for Fab2AV versus 30 percent for FabAV [relative risk reduction 0.

In an observational study of 37 patients with rattlesnake envenomation from the New Mexico regional poison control center, both Fab2AV and FabAV achieved initial control of local effects and managed initial hemotoxicity [ 37 ].

The lower risk of late hemotoxicity following use of Fab2AV makes it attractive for use in patients with rattlesnake envenomation. Although uncommon, late thrombocytopenia and coagulation abnormalities have been associated with serious bleeding and mortality [ ]. In addition, FabAV antivenom did not reverse the thrombocytopenia following a reported timber rattlesnake envenomation [ 49 ].

Prior to the availability of antivenoms active against Crotalinae snakebites and the widespread availability of emergency departments and critical care units, snakebite mortality ranged from 5 to 36 percent in the United States [ ].

After the introduction of Antivenin Crotalidae Polyvalent ACP; Wyeth in the s and the development of widespread availability of emergency and critical care medicine starting in the s, deaths from snakebites dropped to less than 1 percent.

For example, analysis of 23, venomous snake exposures from to reported to the American Association of Poison Control Centers database found a fatality rate of 0. Similarly, no fatalities occurred in a United States registry study of native pit viper snakebites occurring from to [ 54 ].

Thus, the availability of antivenom for most native Crotalinae snakebites combined with other trends in emergency and critical care capability has been associated with a marked and sustained decrease in snakebite mortality in the United States.

Additional observational experience suggests that untreated Crotalinae envenomation is rarely fatal in regions where copperhead bites predominate but can be life- or limb-threatening. For example, an observational study of 81 adult and pediatric patients who were managed without antivenom therapy after snakebite 45 copperhead, 12 water moccasin [cottonmouth], 10 rattlesnake, and 14 unknown reported no fatalities or long-term morbidity [ 55 ].

However, significant acute toxicity did occur, including hemotoxicity 15 patients , skin necrosis 8 patients , respiratory distress requiring endotracheal intubation 3 patients , hypotension 2 patients , and cardiac arrhythmia 2 patients.

Supportive care — Antivenom administration is the mainstay for treatment of envenomation by NA Crotalinae snakes. Pain control — Although evidence is limited, patients with rattlesnake or water moccasin bites whose clinical course suggests that the risk of coagulation abnormalities or thrombocytopenia is low or patients with copperhead bites and minimal hemotoxicity may receive analgesia for mild to moderate pain with acetaminophen or nonsteroidal antiinflammatory medications eg, ibuprofen [ 56,57 ].

Severe pain after snakebite frequently warrants treatment with opioid medications eg, fentanyl or morphine. Coagulation abnormalities and thrombocytopenia — Coagulation abnormalities associated with Crotalinae envenomation is primarily due to thrombin-like enzymes or fibrinogenases within the venom.

Fibrinogen levels decline without a decrease in other clotting factors [ 43,58,59 ]. This pathophysiology contrasts with true disseminated intravascular coagulation DIC , where fibrinolysis is activated by increased levels of endogenous thrombin. Thus, antivenom administration, and not coagulation factor replacement, is the primary treatment for Crotalinae-induced hemotoxicity.

See 'Antivenom therapy' above. Multiple venom components may affect platelets, and the mechanism by which thrombocytopenia occurs is complex [ 59 ]. Transfused platelets and coagulation factors in fresh frozen plasma are inactivated by Crotalinae venom and should be avoided in patients with Crotalinae-induced hemotoxicity unless the patient has significant bleeding that is uncontrolled by high-dose antivenom administration [ 60 ].

If blood products are given in response to acute blood loss, they should be given with additional antivenom to prevent rapid depletion of those components.

Venom-induced thrombocytopenia and venom-induced coagulation abnormalities in the absence of blood loss are not indications for administration of blood products. The classic triad of rhabdomyolysis consists of pigmented granular casts in the urine, a red to brown color of the urine supernatant, and a marked elevation in the plasma CK.

Primary treatment goals consist of fluid repletion and evaluation for significant electrolyte abnormalities hyperkalemia, hyperphosphatemia, hypocalcemia. See "Clinical features and diagnosis of heme pigment-induced acute kidney injury", section on 'Clinical manifestations' and "Prevention and treatment of heme pigment-induced acute kidney injury including rhabdomyolysis ".

Elevated tissue pressures — Elevated tissue pressures may complicate Crotalinae bites. Any dressing, constriction band, splint, cast, or other restrictive covering should be removed.

Venom is usually introduced into the subcutaneous tissues, and most, if not all, edema occurs in this space. Tissue pressures may increase because of the massive amounts of subcutaneous tissue fluid and because the skin has limits to its elasticity.

Swelling, pain, and paresthesias may occur in patients after Crotalinae snakebite, but true elevation in compartment pressure is uncommon. Antivenom administration is the primary treatment in this situation; surgical intervention based on clinical findings alone is inappropriate.

Generally, increased compartment pressures result from this extrinsic pressure and can be reduced with the administration of adequate amounts of antivenom and elevation. Elevation results in the drainage of subcutaneous edema and contributes to the reduction of the source of increased tissue pressure.

See 'Minor envenomation' below. Compartment syndrome — True compartment syndrome with documented elevations of muscle compartment pressure is uncommon after Crotalinae snakebites, and fasciotomy is rarely indicated.

For example, among patients with a snakebite from the North American Snakebite Registry, only eight 2 percent had clinical findings concerning for compartment syndrome and only two 0. Bites to muscles in compartments that are very close to the skin eg, anterior tibial, hand, or foot compartments have a higher potential for compartment syndrome.

For these patients, antivenom and elevation may still reduce compartment pressures by the reduction of extrinsic pressure, but persistent intracompartmental pressures may remain high. The indications for fasciotomy in this context are unclear.

An animal model of direct compartmental injection of venom demonstrated improved outcomes with antivenom alone versus antivenom plus immediate fasciotomy [ 61 ]. If there is a concern for clinically significant increased tissue or compartment pressures, direct measurement with an appropriate device should be performed to guide additional management with antivenom and elevation [ 62,63 ] see "Acute compartment syndrome of the extremities", section on 'Measurement of compartment pressures'.

Further management should be guided by a medical toxicologist and surgeon with extensive experience caring for victims with a snakebite. Full recovery has been described with nonsurgical management of acute compartment syndrome in the hand compartment pressure of 55 mmHg in a patient with a rattlesnake bite to the thenar eminence [ 64 ].

The patient received large amounts of polyvalent Crotalinae antivenom 46 vials total and 20 g of IV mannitol. Neurotoxicity — Neurotoxicity may rarely occur after bites by selected NA rattlesnakes eg, Mohave, Southern Pacific, or timber rattlesnakes. Although antivenom is recommended, it may not reliably reverse neurotoxicity.

See 'Initial stabilization' above and 'Initial treatment' above. Wound management — All patients also require wound management as described below.

Disposition — All patients with signs of envenomation require admission for further observation or for treatment with antivenom and supportive care.

Hospitalization is also warranted in the United States for exotic, non-United States snakebites, even in the setting of initially normal clinical appearance. See "Snakebites worldwide: Clinical manifestations and diagnosis".

At discharge, patients who have received antivenom should also receive the following instructions and be scheduled for recommended follow-up:. Minor envenomation — Patients with minor envenomation after an NA Crotalinae snakebite have swelling that is localized to the bite site, and do not have other signs of envenomation should not routinely receive antivenom.

Bites to the face or neck are an important exception. See 'Initial treatment' above. Management should focus on pain control, wound care, immobilization and positioning of the bite site with close monitoring for progression of swelling or development of hemotoxicity or other signs of envenomation algorithm 1 :.

Patients with rattlesnake or water moccasin snakebites whose clinical course suggests that the risk of coagulation abnormalities or thrombocytopenia is low and patients with copperhead bites and minimal hemotoxicity may receive nonsteroidal antiinflammatory medications eg, ibuprofen [ 56,57 ].

Severe pain warrants treatment with IV opioid medications eg, fentanyl or morphine. See "Tetanus-diphtheria toxoid vaccination in adults". The leading edge of swelling and tenderness, when apparent, should be marked and reassessed every 15 to 30 minutes.

Alternatively, extremity circumference can be measured both distal and proximal to the bite site. A marker is used to outline the location of the tape measure on the skin so the same locations are used consistently [ 34 ]. Bedside superficial debridement of hemorrhagic bullae should they occur to permit recognition of underlying necrosis and to help decide further intervention has been proposed [ 65 ].

However, we do not recommend this approach because there are insufficient data demonstrating benefit or evaluating the risks, such as infection, of unroofing intact bullae. Antibiotic prophylaxis is not indicated. Although snakebites may result in the inoculation of bacteria, infection is rare.

A retrospective analysis of over rattlesnake bites reported to a regional poison control center found an infection rate of at most 1 percent based, in most cases, on clinical appearance [ 66 ]. These results may overestimate the frequency of infection in snakebites because inflammation from venom effects may track up lymphatic channels and mimic cellulitis.

Thus, only patients with established infections or heavily contaminated wounds should receive antibiotics [ 2 ].

Empiric treatment should cover Salmonella species and common human organisms eg, Staphylococcus aureus and group A streptococcus until wound culture results are available. During hospital care, we advise elevation of the extremity to reduce acute swelling.

See 'First aid' above. Patients with confirmed copperhead bites appear to be at a lower risk for systemic toxicity and progressive swelling but may have impairment of function due to swelling and pain in the involved extremity long enough to cause significant short-term morbidity eg, inability to work or attend school.

In one study, the duration of this impairment was a median of three weeks with a range of three days to four months [ 67 ]. Some experts have suggested that antivenom may provide short-term benefit to patients with mild copperhead envenomation with acceptable risk, primarily minor adverse effects, and increased cost of care.

However, more data are needed to identify which patients are most likely to benefit and to establish if antivenom improves function enough to offset the potential risk of serious adverse effects, such as anaphylaxis, when only local venom effects are present.

As an example, in one small trial of 74 patients with copperhead bites, treatment with polyvalent Crotalinae ovine immune Fab FabAV, CroFab modestly improved limb function and reduced use of opioid pain medication at two weeks but did not shorten the time to full recovery compared with placebo [ 67 ].

Although the benefit regarding local venom effects in rattlesnake envenomations has not been studied, there is no reason to believe that similar benefits would not apply to these cases as well.

Patients who received FabAV had more minor adverse events eg, pruritus, urticaria, nausea, dizziness, or fever but no severe effects. Platelet and fibrinogen studies should be repeated every six to eight hours after the initial set of studies.

Patients with progressive swelling or abnormal coagulation testing during the observation period should receive antivenom as described below. They also warrant assessment for rhabdomyolysis.

See 'Antivenom therapy' above and 'Supportive care' above. Potential dry bite — Up to 25 percent of patients with Crotalinae bite will not develop clinical envenomation. All patients presenting with report of potentially venomous snakebites should be placed on a cardiac monitor, have initial laboratory studies obtained, and observed for signs of toxicity eg, progressive swelling, tachycardia, hypotension, or bleeding.

All other patients warrant observation for 8 to 12 hours algorithm 1. It is likely that no significant envenomation has occurred if all of the following criteria are met:. SERUM SICKNESS — Serum sickness occurs in about 2 to 3 percent of patients receiving either FabAV or Fab2AV.

Section Navigation. Facebook Twitter LinkedIn Syndicate. Minus Related Pages. Photos courtesy of Sean P. First Aid Workers should take these steps if a snake bites them: Seek medical attention as soon as possible dial or call local Emergency Medical Services [EMS].

Antivenom is the treatment for serious snake envenomation. The sooner antivenom can be started, the sooner irreversible damage from venom can be stopped. Driving oneself to the hospital is not advised because people with snakebites can become dizzy or pass out. Take a photograph of the snake from a safe distance if possible.

Identifying the snake can help with treatment of the snakebite. Keep calm. Inform your supervisor. Apply first aid while waiting for EMS staff to get you to the hospital. Lay or sit down with the bite in a neutral position of comfort.

Remove rings and watches before swelling starts. Wash the bite with soap and water. Cover the bite with a clean, dry dressing. Do NOT do any of the following: Do not pick up the snake or try to trap it. NEVER handle a venomous snake, not even a dead one or its decapitated head. Do not wait for symptoms to appear if bitten, get medical help right away.

After a natural disaster, snakes may have been forced from their natural habitats and move into areas where they would not normally be seen or expected. When you return to your home, be cautious of snakes that may have sought shelter in your home.

If you see a snake in your home, immediately call the animal control agency in your county. If you are walking in high water, you may feel a bite, but not know that you were bitten by a snake. You may think it is another kind of bite or scratch. Pay attention to the following snake bite signs and symptoms.

Skip directly to site content Skip directly to search. Español Other Languages. How to Prevent or Respond to a Snake Bite. Minus Related Pages. Highlights If you see a snake in your home, immediately call the animal control agency in your county.

Be aware of snakes that may be swimming in the water or hiding under debris or other objects.