“Red on yellow, or red on black?”
Wesley Priddy, MD, USF MCOM Emergency Medicine Residency
Jacob Stritch, MD, USF MCOM Emergency Medicine Residency
Elias Eid, MS4, University of Central Florida College of Medicine
Antonio Lazcano, MD, Tampa General Hospital/Team Health
Justin Arnold, DO, Associate Professor of Emergency Medicine, Medical Director Florida Poison Control Center Tampa
Case Presentation:
A 36 year old female presented as a transfer from an outside facility for symptomatic Coral snake envenomation. The patient stated that she was bitten by a snake at approximately 1700 on her right big toe while moving furniture around in her garage. The snake was reported to have been attached to her for approximately 30 seconds. She stated that the snake was red, yellow, and black, but she was unsure what kind of snake it was. She was shown pictures of snakes at the outside facility and reportedly identified the snake as a Coral snake. The patient then began to experience paresthesia radiating from the site of the bite up to her foot, and then progressed up to her mid-thigh. The transfer process was then initiated from the outside facility to our emergency department. Upon presentation to our hospital the patient confirmed the above and was complaining of the paresthesia as mentioned above as well as significant pain of the same area. She denied any significant past medical history or surgeries. Social history negative for drinking, smoking, or drug use. Review of systems was significant for bite wound in addition to the above, but otherwise negative. She was given fentanyl for pain control and the Florida Poison Information Center of Tampa was consulted for recommendations regarding antivenin.
Case Discussion:
Coral snake envenomation is a rare but clinically significant cause of emergency department visits in the United States. Coral snakes are a part of the Elapidae family of snakes, as opposed to the Crotalidae, which are a more common cause of snake envenomation. Other members of the elapid family include the King cobra and the death adder. Taxonomy is important in this case because antivenin such as Cro-Fab was designed to treat envenomation from crotalid snakes, but not elapids which have significantly different venom composition. Whereas members of the crotalid family have a mainly hemotoxic venom, elapids have a mainly neurotoxic venom.1 Effects of the venom are apparent on physical exam, with much more significant soft tissue reaction at the site of the bite with, for example, a rattle snake compared to a Coral snake. As with other snakes, not all bite victims are envenomated and some victims receive a “dry bite”.
Diagnosis of Coral snake bites can be challenging given that it relies on patient’s memory of band patterns at a time when they likely have other things on their mind. An additional challenge is the similarity of the Coral snake band pattern compared to the non-venomous King snake. This similarity led to the development “Red on yellow, kill a fellow; red on black friend of Jack.” Clinical experience has shown this rhyme to be often misremembered in practice. Additionally there is can be some phenotypic variation that can lead differently colored scales within the bands, meaning that there can be black scales within a red band even in a Coral snake. A much easier and more effective method is to identify the color of the snout, which is black in a Coral snake.2
Onset of symptoms can be any time from 140 minutes to 13 hours after the time of the bite.3 Presentations are variable but predominately neurologic in nature with early involvement of the cranial nerves. The bite wounds themselves often lack significant swelling and fang marks may not be visible, but bites should not be assumed to be dry just because of lack of significant local tissue reaction3,4. Alteration of mental status has not been described throughout this process. While antivenin can halt the progression of symptoms, it does not reverse existing symptoms, so early administration is key.
Given the rarity of these envenomations, antivenin can be hard to come by. In addition, the only manufacturer has discontinued production of the antivenin. The FDA tests and approves an expired lot for production each year for use while alternative antivenins are being developed.5 National or local poison control centers should be contacted for information on dosing on a case-by-case basis, but generally a starting dose of 5 vials are given to symptomatic patients. The antivenin is equine based, so patients receiving it should be monitored for the development of both immediate hypersensitivity reactions as well as the development of serum sickness. The risk of serum sickness escalates in a dose-dependent fashion, with a peak between days 7 to 14 after administration.
Lab studies are rarely helpful in the workup of these envenomations. Due to the mainly neurotoxic effects of the venom, workup for coagulopathy and hemolysis is often unremarkable. An exception is that, based on clinical experience, the most frequent co-ingestion with these envenomations is ethanol.6 Check levels as clinically indicated. Some authors suggest a chest x-ray in patients with bulbar signs with a concern for aspiration pneumonia.7 Additional imaging can be obtained to rule out retained fang.8
Many misconceptions exist in popular culture regarding first aid for snake bites such as commercial venom extraction kits, tourniquets, electric shock therapy, and attempting to suck the venom out of the wound. None of these methods are currently recommended.9,10 The affected area can be splinted if possible and washed with soap and water, but the mainstay of prehospital treatment should be focused on getting symptomatic patients to a facility with antivenin for quick administration. As with other puncture wounds, tetanus immunization should be updated if indicated, but routine antibiotic prophylaxis for these wounds is not indicated.11 The incidence of wound infection for snake bites is less than 10%. Antibiotic prophylaxis can be considered if the wound was exposed to oral flora from an attempt to suck venom from the wound.12
These bites can be quite painful as well as distressing for the patient who is faced with the prospect of respiratory failure. Opioids are generally recommended against due to their potential to diminish the sensitivity of the patient’s neurologic exam as well as the risk of potentiating respiratory depression.13 The mainstay of pain control in envenomated patients is administration of antivenin which provides rapid pain relief, but other non-opioid analgesics can be used when awaiting antivenin.14
Disposition for these patients is to the ICU for the first 24 hours after envenomation for hourly pulmonary function testing and monitoring for respiratory depression15.
Case conclusion:
The patient was admitted to the ICU for further monitoring and management. Routine labs were significant for an incidental minor macrocytic anemia but otherwise unremarkable. She received 5 vials of Coral snake antivenin which halted progression of symptoms. There were no signs of immediate hypersensitivity reaction to the antivenin. The patient was discharged after a 24 hour observation period with return precautions and follow up with her primary care physician.
Take home points:
Coral snakes have black noses, correct identification is key to the diagnosis!
Cro-fab does not work for these bites, you may have to transfer to a facility with the correct antivenin.
Snake bites rarely get infected, routine antibiotic prophylaxis is not recommended.
Patients should be monitored closely for bulbar weakness and respiratory depression.
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About the author: Dr. Wesley Priddy, MD is a third-year emergency medicine resident at the University of South Florida
Post edited by Dr. Michael Weaver, MD