First remove any tentacles
tentacles separated from medusae can still emit venom
4-5% acetic acid/vinegar solution should be applied to the injured area for at least 30 seconds.
Pain control
Supportive measures for minor envenomations
Ice recommended but heat may actually work better
Antihistamines and steroids for hypersensitivity reaction
Do NOT pressure bandage
Antivenom for life-threatening envenomations
Bovine IgG Fab with 20,000 units/ampule
Avoid treating with fresh water, alcohol, methylated spirits, or urine as these have shown to increase nematocyst firing. 
tentacles separated from medusae can still emit venom
Ice recommended but heat may actually work better
Bovine IgG Fab with 20,000 units/ampule
Cardiac arrest
undiluted antivenom administered as an IV Push: up to 6 vials
if no response then give magnesium IV (0.2mmol/kg, max 10mmol in adults)
Hypotension, tachycardia, shock, arrhythmia
dilute 3 amps antivenom in 100mL NS and run over 20 minutes
can repeat for a total of 6 vials
Intractable pain
give 1 amp diluted in 100mL NS run over 20 minutes
undiluted antivenom administered as an IV Push: up to 6 vials
if no response then give magnesium IV (0.2mmol/kg, max 10mmol in adults)
dilute 3 amps antivenom in 100mL NS and run over 20 minutes
can repeat for a total of 6 vials
give 1 amp diluted in 100mL NS run over 20 minutes
Anti-venom can cause serum sickness 4-14 days after administration
Box jellyfish envenomation
Toxins
Fire coral envenomation
Ciguatera
Crown-of-Thorns starfish envenomation
Scombroid
Stonefish envenomation
Tetrodotoxin 