An envenomation or antivenom administration can cause anaphylaxis, and this may initially be difficult to distinguish clinically. Signs include hypotension, bronchospasm, facial and airway swelling, pruritus, urticaria, nausea, vomiting, and diarrhea. Most reactions occur within 15–30 minutes and nearly all occur within six hours. A recipient of antivenom should be pretreated with 50–100 mg of IV diphenhydramine (1 mg/kg in children). The initial dose of antivenom should be administered no faster than one vial over five minutes. If antivenom is necessary and anaphylaxis develops, administer 0.1–0.2-mL aliquots of antivenom alternated with 0.03–0.1-mg IV doses of epinephrine. Alternatively, an epinephrine drip may be started and titrated to maintain a heart rate less than 150 beats/min.

Phylum: Cnidaria

Class: Cubozoa (Cubozoa species produce the highest morbidity and mortality of all Cnidaria.¹)

Sea Wasp or Marine Stinger (Chironex fleckeri)

Location: Indo-Pacific Ocean, southeast United States (rare)

Epidemiology: Ninety-two percent of stings occur during “stinger season” (Australian summer, Oct. 1–June 1) between 3 and 6 p.m., with 83 percent occurring in <1 m of water.³

Appearance: The sea wasp has a large bell (body) measuring an average of 25 to 30 cm in diameter. Each of its four corners contains about 15 tentacles that contain millions of “stinging cells” called nematocysts (ie, cnidocytes) and can measure up to 3 m in length.¹

Pathophysiology and Symptoms: Contact with the tentacles causes rapid development of a pruritic/burning, erythematous maculopapular rash with a characteristic “ladder-rung” pattern. Severe pain is the most common complaint and can last for several hours due to sustained muscle contractions caused by myotoxins within the venom.⁴ This can result in rhabdomyolysis, depending on the duration and intensity of the contractions. Although uncommon, cardiovascular collapse can occur due to a combination of dysrhythmias (due to hyperkalemia) and osmotic dysregulation of endothelial and cardiac tissues from pore-forming toxins within the venom.⁵ This ultimately leads to cardiogenic pulmonary edema, severe hypotension, and death in as few as 30 seconds.⁶ Additional complications include altered mentation, dizziness, ataxia, and hemolysis.

Management: Pain should be managed with vinegar, HWI, local lidocaine (infiltration or topical), and/or Stingose solution (pain relief has been shown within five seconds of application).⁷ Compressive dressings are controversial and have recently been recommended against in the management of all Cnidaria envenomations due to demonstrated increase in venom release from nematocysts.^1,8,9 Obtain an ECG, serial cardiac biomarkers, and chemistry panel to assess for electrolyte abnormalities. Box jellyfish antivenom is available and has been shown to prevent all toxicity in animal studies when administered prophylactically.¹⁰ However, current beachside (ie, Surf Life Saving Australia’s beach lifeguard group) dosing recommendations of three vials intramuscularly at three separate sites may be too small a dose and too slow a route. Early IV administration of antivenom in large doses—initial treatment of one to three vials diluted 1:10 with saline, along with IV magnesium sulfate (0.2 mmol/kg, max 10 mmol in adults) bolused over 5–15 mins—is recommended if there are any signs of severe toxicity, intractable pain, or cardiac arrest. But even this may be too small a dose, and further research is needed.^11,12 The current maximum dose of antivenom is six vials undiluted and should be given via rapid IV push if the patient is in cardiac arrest.¹¹