What toxin is responsible for the most serious clinical effects experienced by patients bitten by the creature in this photo?

  1. latrotoxin
  2. Conotoxin
  3. Helothermine
  4. Tetrodotoxin
  5. Verrucotoxin

Answer:  4 – Tetrodotoxin


The pictured creature is a blue-ringed octopus (Hapalochlaena lunulate Hapalochlaena maculosa), and it secretes tetrodotoxin in its saliva (1). Tetrodotoxin binds voltage-gated sodium channels in muscles and nerve tissue, inhibiting action potential propagation and resulting in flaccid paralysis and death due to respiratory failure (2).  The blue-ringed octopus has a beak-like structure

near its mouth that creates a small puncture wound, allowing for injection of venom from the salivary gland (3). Direct contact with the octopus’s tentacles does not cause envenomation. The blue ringed octopus is found in the Indo-Pacific oceans, particularly along the Australian coasts, and interestingly displays its colors only when threatened (4,5).


Presentation: (3,4,6)

  • Puncture wound at the site which can be red and itchy
  • Perioral and intraoral paresthesia
  • Blurry vision
  • Nausea and vomiting
  • Ataxia and weakness
  • Within 30 minutes to several hours, progression to flaccid paralysis and respiratory failure, cardiac arrest, and death if untreated
  • Does not affect mental status
  • Paralysis lasts 4-10 hours, and treated patients recover fully in 2-4 days

Treatment: (3,4,6)

  • Local wound care and tetanus prophylaxis
  • Close observation for symptom development
  • Early airway management and supportive care for respiratory paralysis
  • Fluid resuscitation and vasopressors if needed for hypotension
  • No antivenom available
  • If asymptomatic after 6 hours, can discharge from the Emergency Department

Bedside Pearls:

  • Symptoms start within minutes and include oral paresthesia, vomiting, and weakness but can quickly progress to flaccid paralysis and respiratory failure.
  • Management includes supportive care with a focus on respiratory support.
  • Significant hypotension can occur and should be treated as needed.
  • There is no antidote for tetrodotoxin poisoning.
  • Use sedating agents while the patient is receiving mechanical ventilation as the venom does not cause CNS depression.
  • Patients have good clinical outcomes if symptoms are recognized quickly and they are supported with mechanical ventilation during the paralysis.
  • Most patients have complete resolution of symptoms within 2-4 days.

This post was peer reviewed on behalf of ACMT by Bryan Judge, Louise Kao, and David Wood.


  1. Lorentz MN, Stokes AN, Robler DC, et. al. Tetrodotoxin. Curr Biol. 2016 Oct 10;26(19) PMID 27728785
  2. Whitelaw BL, Cooke IR, Finn J, et. al. The evolution and origin of tetrodotoxin acquisition in the blue-ringed octopus (genus Hapalochlaena). Aquat Toxicol. 2019 Jan;206:114-122. PMID 30472480
  3. Hoffman R, eds. (2015) Goldfranks’s Toxicologic Emergencies, 10th ed. Chapter 119: Marine Envenomation. New York, NY: McGraw-Hill.
  4. Cavazonni E, Lister B, Sargent P, et. al. Blue-ringed octopus (Hapalochlaena sp.) envenomation of a 4-year-old boy: a case report. Clin Toxicol (Phila). 2008 Sep;46(8):760-1. PMID 19238736
  5. ]Mäthger LMBell GRKuzirian AM, et. al. How does the blue-ringed octopus (Hapalochlaena lunulata) flash its blue rings? J Exp Biol. 2012 Nov 1; 215(Pt 21):3752-7. PMID 23053367
  6. Hornbeak KB, Auerbach BS. Marine Envenomation. Emerg Med Clin North Am. 2017 May;35(2):321-337. PMID 28411930
Ashley Mazo, MD

Ashley Mazo, MD

Fellow, Pediatric Emergency Medicine
Department of Emergency Medicine
Carolinas Medical Center, Charlotte, NC
Ashley Mazo, MD

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Christine Murphy, MD

Christine Murphy, MD

Associate Professor of Emergency Medicine
Medical Toxicologist
Department of Emergency Medicine
Atrium Health’s Carolinas Medical Center