redback spider antivenom effective

Redback antivenom: What does the science say? | Day 236

Last night my boyfriend looked over my shoulder at the bedroom wall, said “uh-oh” and continued with “there is a spider.”

Naturally, I fled the room without looking. He said it was medium-sized! You might think ‘medium’ is not too bad, but if you’ve grown up in north-eastern Europe where a ‘big’ spider is the size of your thumbnail, Australian arachnids shake that perspective a fair bit. And the brain of an arachnophobic really doesn’t care whether the spider is dangerous or not; besides, dangerousness doesn’t correlate with size, while fear levels do.

For example, I’m mortally afraid of the benign huntsman spiders, because they are huge. Meanwhile, the one time I found one of the most dangerous spiders in the world on my couch, I didn’t even know what it was, although now I know that the characteristic red stripe on a black body means trouble.

The redback spider (Latrodectus hasselti) belongs to the same genus as the black widow spiders found in America. Its venom contains a potent nerve toxin called latrotoxin which causes intense pain and sweating by stimulating neurotransmitter production. This reaction is known as latrodectrism.

The spider has killed some people before, but no deaths in Australia have been registered since the introduction of antivenom in 1956. Around 250 antivenom treatments are administered each year. Because the main result of a redback bite is pain, doctors also use painkillers to alleviate the suffering of the patient, however most painkillers have limited effectiveness, and do not counteract the venom.

Good thing they developed that antivenom, isn’t it?

Except, according to Calvary Mater Hospital clinical toxicologist Prof Geoff Isbister, the antivenom for redback bites does very little. In 2008 he and colleagues performed a randomised trial to see whether injecting redback antivenom in the vein was more effective than performing an intramuscular injection. The results showed basically no difference, which, along with blood sample analysis that detected no antivenom in the blood after intramuscular injection, as well as data on how the treatment doses have been increasing over years, made the researchers think whether both approaches might be equally ineffective.

In order to investigate this suspicion, a few years later Isbister actually managed to perform a placebo-controlled trial with 224 redback spider bite patients – half of them received a placebo injection, and half received the antivenom. The results? No statistically significant difference in symptom reduction for the two groups.

Dr Isbister doesn’t prescribe antivenom to his redback bite patients any more.

However, this approach has been criticised by other toxicologist and clinicians. Dr Julian White believes that until the trial has been replicated, not using antivenom is foolish. He argues that, while it’s not a controlled trial, there is ample anecdotal and retrospective evidence from several decades of seeing patients in a clinical setting get better after the injection of antivenom, and, since the risk of dying from a redback bite is extremely low, the primary aim of a treatment is to reduce distress, not necessarily save lives. He also notes that just because you can’t detect antivenom in the blood after injecting it in the muscle, doesn’t mean it still isn’t working where it is needed – around the nerve connections where the venom is doing its nasty work.

So, it appears that right now it could go either way. Redback antivenom might be effective, it might not, but I wouldn’t be surprised if this time the truth actually is somewhere in the middle – it helps a bit, but not much.

However, don’t quote me on that. Let’s wait for more robust scientific research in the next few years. The controversy is definitely real.

3 thoughts on “Redback antivenom: What does the science say? | Day 236”

  1. “Let’s wait for more robust scientific research in the next few years.”
    I wonder, if there are any ongowing trials or reaserch of some kind, who’s financing it. For any kind of question, I wouldn’t know how to start finding out (besides using search engines with “doing reaserch on question of interest”).

  2. Whoa, so they don’t even know if the antivenin formulated for one of the most dangerous spiders in the world works or not… I’m not an arachnophobe, but that is a little worrying.

    I think an interesting question here is whether the lack of any deaths from the bite since the introduction of the antivenin is due to the antivenin or merely just a result of more readily available and effective medical care. Considering that an estimated 2,000 to 10,000 bites occur per year with only 250 antivenin treatments.

    Another question I have is when the last confirmed Redback spider death actually occurred? From admittedly a very brief google search every page I found just repeats the same line there have been no confirmed deaths since the introduction of the antivenin without actually discussing when the last occurred.

    1. Josh, it’s the right question to ask. Lack of deaths is correlated with introduction of antivenom, but correlation isn’t causation.

      Speaking of the last registered latrodectrism death, it’s behind a paywall, but this paper mentions it was in 1955, a year before the introduction of the antivenom.

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