Deadly Stinger
June 15,
2009 -- 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.
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