Snake Envenomation: Eastern Copperhead

January 2026
In this VETgirl online veterinary continuing education blog, Lexi Dickens, BS, LVT, RVT, VTS (ECC) breaks down how to recognize and respond to snake bite envenomation. Since a majority of the US states are home to venomous snakes, bites are bound to happen! Learn the clinical signs of a snake bite and treatment options in dogs and cats!

By Lexi Dickens, BS, LVT, RVT, VTS (ECC)
Senior Patient Care Training Coordinator, BluePearl Pet Hospital, Cary, NC

In the US, 47 states are home to venomous snakes and it is estimated that around 150,000 dogs and cats are bitten by snakes every year.^1-3 Up to 90% of these bites are reported to happen between the months of April and October.² Snakes in the Crotalidae family, also referred to as “pit vipers”, make up a large percentage of reported bites and include species such as rattlesnakes, cottonmouths, and copperheads.¹ Pit vipers are known for their diamond shaped heads, elliptical pupils, retractable fangs, and heat sensing “pit” between their eyes and nose.¹

Species in the Crotalidae family can control the amount of venom that is released with each bite. This means that this family of snakes may deliver a “dry bite” (i.e., a bite that does not release venom), which is report to happen in about 25% of Crotalidae bites.¹

A suspected “dry bite” to the side of a canine’s face. Note the lack of swelling or bruising (Photo courtesy of Lexi Dickens)

If venom is released, the amount is determined by multiple factors including how recently the snake last expelled venom, how severe the threat is to the snake, and the snake’s age and size.^1,3 When snakes hunt, they swallow their prey whole and the venom, which contains enzymes such as venom hyaluronidase and collagenase among other factors, is used to immobilize and “pre-digest” their prey.^1,2 Copperheads (Agkistrodon contortrix) have venom that contains zinc metalloproteinase, also known as fibrolase, which has fibrinolytic activity. Additionally, there are thrombin like enzymes that can interfere with clot formation and interrupt the coagulation cascade by inhibiting the activation of factor VIII.¹ Venom also has inflammatory mediators such as arginine ester hydrolase, which can cause increased clotting times.²

Patients may present with a snakebite that was witnessed by the owners; others may have a vague history where the owner did not see a snake or witness the bite. Canine patients are often bitten on the muzzle, lip, or distal limbs. Feline patients are often bitten on a forelimb or muzzle. It is important to note that feline patients are more resistant to the effects of venom based on a venom to body weight ratio (e.g., mg venom/kg of body weight). However, cats generally present in more critical condition as they tend to run and hide after an injury resulting in a delayed onset of treatment.² It is important to inspect the patient for the presence of fang puncture wounds over their entire body. Puncture wounds can be painful, bleeding, have serous discharge, and often already have bruising around them by the time of presentation.

A copperhead bite with envenomation on the upper lip of a canine patient. (Photo courtesy of Lexi Dickens)

Bites that release venom display swelling within the first hour but it can develop sooner with severe envenomation or agonal bites where the snake releases all of its venom.¹ Other common presenting clinical signs from snake envenomation can include profound swelling, increased salivation, petechia, vomiting, diarrhea, hypotension, and altered mentation, though clinical signs can vary depending on time since the bite, and severity of envenomation.^1,2,4

Petechiation and ecchymosis in the inguinal region of a canine patient (Photo courtesy of Lexi Dickens)

Frequent monitoring of progression of bruising or swelling is important and may include outlining bruising, petechia, or ecchymosis to indicate progression or spreading.

Bruising that is being monitored for spreading by outlining the existing bruise.
(Photo courtesy of Lexi Dickens)

Initial treatments should include pain management, often with a full mu opioid such as methadone or hydromorphone. Due to the tissue damage and activation of inflammatory mediators, patients often present in significant pain. NSAIDs should be avoided due to concerns of interfering with platelet aggregation and worsening of any clotting abnormalities induced by the envenomation.^2,3 Ideal diagnostics should include a complete blood count (CBC) with a manual differential, serum chemistry with electrolytes, coagulation profile, and urinalysis. Common abnormalities can include mild anemia, leukocytosis, thrombocytopenia, hypokalemia, hematuria or hemoglobinuria, proteinuria, as well as prolonged prothrombin time (PT) and partial thromboplastin time (PTT). If there is access to thromboelastographic (TEG) testing, it should be utilized in patients exhibiting signs of venom-induced consumptive coagulopathy (VICC) or severe envenomations that are not responsive to initial treatment. TEG has a much higher sensitivity than PT and PTT and can provide more information, including thrombin formation and fibrinolysis.⁶ Abnormalities that can be found on a manual differential include thrombocytopenia as well as echinocytes, whose presence may be an indicator of envenomation.

Echinocytes seen after a copperhead envenomation. (Photo courtesy of Lexi Dickens)

Diagnostics should be used to monitor trends, progression of disease, and response to intervention.^1,2

Many patients with snake envenomation are hospitalized for continued care and monitoring. Staple treatments during hospitalization may include continued pain management with titratable analgesia, such as a fentanyl CRI and fluid therapy that is titrated based on the level of hypotension. Patients that have severe hemorrhage, thrombocytopenia, or severe hypoproteinemia may benefit from fresh whole blood administration.³ Serial diagnostics should be performed alongside dedicated nursing care to monitor for delayed complications from the envenomation, such as persistent or worsening hypotension, anemia, acute kidney injury, disseminated intravascular coagulation, cardiac arrhythmias, or VICC.³ Antivenin administration aids in pain management, as well as correcting coagulopathies and hypoproteinemia. It should be remembered that antivenin cannot reverse any tissue damage or necrosis.³

Antivenin in veterinary medicine is derived from hyperimmunized ovine or equine donors. Antivenin for different species of snakes can be created based on which venom the donor is exposed to. After sufficient antibody titers are met in the hyperimmunized donors, their plasma is collected, pooled, and purified.⁵ Antivenin (Crotalidae) Polyvalent referred to as ACP contains whole IgG molecules and equine serum albumin.

An example of ACP Crotalid Antivenin. This product comes in a liquid form rather than lyophilized. (Photo courtesy of Kellen O’Rourke-Owens)

IgG products have a large molecular size and, therefore, a slower onset of diffusion and clearance throughout the body, allowing the antivenin to remain in circulation for a longer period. The Fc region which is part of the antibody that interacts with cells, aids in longer circulation, however this portion also increases the risk of acute hypersensitivity reactions.⁵ When the Fc portion is removed from whole immunoglobulins and digested with pepsin it will yield one F(ab’)2 (fragment antigen binding) fragment that contains two antigen-binding site. These products have a smaller molecular size and allow for rapid distribution throughout the body; however, they do not remain in circulation as long, which may result in the need for repeat administration. The removal of the Fc portion may result in a decreased chance of an acute hypersensitivity reaction during administration.^3,5 It is important to be aware that while antivenin is a staple treatment of snake envenomation, there are additional risks, aside from acute hypersensitivity reactions. With multiple doses of antivenin, regardless of IgG or F(ab’)2, patients can suffer from serum sickness which in essence is a delayed hypersensitivity reaction.¹

Continuous monitoring and attentive nursing care are essential for early recognition of patient deterioration and secondary complications such as serum sickness, disseminated intravascular coagulation, venom induced consumptive coagulopathy, or multiple organ dysfunction syndrome (MODs). Successful management of pit viper envenomation depends on a thorough clinical assessment, prompt and appropriate intervention, and vigilant monitoring of the patient’s response to treatment. Core components of care include effective pain management, serial diagnostics evaluations, and timely administration of antivenin. By adhering to these principles, veterinary teams can optimize outcomes with copperhead envenomation.

Want to take a deeper dive into learning about what your coagulation results could mean? Read our VETgirl blog on How to Interpret Coagulation Tests in Dogs and Cats HERE. And if you want something handy to reference in the clinic, check out our Clinical Transfusion Resource Bundle HERE!

Abbreviations
ACP Antivenin (Crotalidae) Polyvalent
CBC complete blood count
MODs multiple organ disfunction syndrome
NSAID non-steroidal anti-inflammatory drug
PT prothrombin time
PTT partial thromboplastin time
TEG thromboelastographic
VICC venom-induced consumptive coagulopathy

References
1. Gilliam LL, Brunker J. North American snake envenomation in the dog and cat. Vet Clin North Am Small Anim Pract. 2011;41(6):1239–1259. doi.org/10.1016/j.cvsm.201..08.008.
2. Peterson ME. Snake bite: pit vipers. Clinical Tech Small Anim Pract. 2006;21(4):174-82. doi.org/10.1053/j.ctsap.2006.10.008.
3. Armentano RA, Schaer M. Overview and controversies in the medical management of pit viper envenomation in the dog. J Vet Emerg Crit Care (San Antonio). 2011;21(5):461-70. doi: 10.1111/j.1476-4431.2011.00677.x.
4. McCown JL, Cooke KL, Hanel RM, et al. Effect of antivenin dose on outcome from crotalid envenomation: 218 dogs (1988–2006). J Vet Emerg Crit Care (San Antonio). 2009;19(6):603-10. doi: 10.1111/j.1476-4431.2009.00487.x.
5. Carotenuto SE, Bergman PJ, Ray JR, et al. Retrospective comparison of three antivenoms for the treatment of dogs with crotalid envenomation. J Am Vet Med Assoc. 2021;259(5):503-509. doi: 10.2460/javma.259.5.503.
6. Lee JM, Jung YS, Kim YJ, et al. Thromboelastographic evaluation in dogs with Asian pit viper (Gloydius) envenomation. J Vet Med Sci. 2023;85(11):1226-1230. doi: 10.1292/jvms.23-0100. Epub 2023 Oct 19.