A box jellyfish antivenom is proven ineffective against the animal's deadly sting. A long-used box jellyfish antivenom is unlikely to actually save lives, suggests new Australian research. And one expert says findings like this mean we need to improve our testing of antivenom effectiveness. A team publishing online in the journal Toxicology Letters say venom from the box jellyfish acts so rapidly that any antivenom is unlikely to be protective. "The box jellyfish is by far the most lethal organism in the world," says clinical toxicologist Geoff Isbister of Menzies School of Health Research in Darwin. He says a sting from a box jellyfish is like "millions of hyperdermic injections of venom" and can cause cardiac arrest and death. Isbister says there has long been a question mark over the clinical effectiveness of CSL's antivenom for the Australian box jellyfish, Chironex fleckeri, which has been used since the 1970s. "There's never been a case where someone could say that antivenom saved a life," said Isbister.