lunes, 15 de junio de 2009
Antivenoms Can't Stop Deadly Jellyfish Sting
Box jellyfish kill around one person in Australia every 2 to 3 years, mainly children. And a long-used box jellyfish antivenom is unlikely to actually save lives, suggests new Australian research.
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.He says people given the antivenom have still died, and others have survived with resuscitation, even without the antivenom.
Isbister and colleagues found that when CSL antivenom was mixed with venom and injected into the rat, all the toxins in the venom were bound, and the rat did not die.
But, says Isbister, in real life, people are exposed to the venom first, before the antivenom.
To mimic this situation, the researchers administered the venom first, and found the rat died within 30 seconds to 2 minutes.
"The rats died so quickly you couldn't even give them the antivenom fast enough," said Isbister.
They even found that when they gave the antivenom first, it did not protect against the venom.
Isbister says the findings suggest the antivenom was unlikely to be effective.
"Ultimately in the real setting, even giving antivenom after they've been stung is probably not going to work," said Isbister.
Isbister said other studies are finding similar limitations with other antivenoms.
He says his own research suggests antivenom is ineffective in relieving the pain of redback spider bite. As a result, he and colleagues have started an NHMRC-funded placebo-randomised controlled trial of redback antivenom.
Other research on snake antivenom shows it does not help stop bleeding, says Isbister.
He says one reason it is important to make sure antivenom is effective in patients is to ensure the benefits outweigh the risks. "Antivenom is not risk free. It can cause anaphylaxis and allergic reactions," said Isbister.
CSL says it needs more time to analyze the new research."We are always interested to see papers like this and we take account of their findings," a company spokesperson said. "However," they added, "we cannot make conclusions about what should happen in a clinical setting as a result."
"The clinical management of box jellyfish envenomation is highly dependent on the circumstances, for example remoteness of the incident, and is a matter for the treating doctor to decide."
The ultimate evidence that box jellyfish antivenom is ineffective in patients would come from a placebo-controlled randomized controlled trial, in which some patients are given antivenom, and some aren't.
But, given the deadly nature of box jellyfish venom, Isbister says this would be regarded as unethical.
Isbister says he has been criticized by some who believe his negative comments about antivenoms are threatening antivenom research and production. But he emphasizes that some antivenom is really important, such as that which protects against the neurotoxic effects of taipan bite.
He would like more realistic tests to be carried out in the research and development of antivenoms.
"You can't assume that's something is going to be effective even if it binds the toxins," said Isbister.
Box jellyfish kill around one person in Australia every 2 to 3 years, mainly children. For now, prevention is the best cure.
"Don't let children swim when there's jellyfish around," Isbister said.