This non-life threatening envenomation (latrodectism) classically presents with a triad of localized pain, sweating and piloerection (goosebumps)
Clinically the main issue is pain, which may be difficult to manage and can last up to 1 week
The efficacy of redback spider antivenom has recently been questioned and may not provide any additional pain relief over using analgesia alone
Signs and Symptoms
Consider the diagnosis in any child with abrupt onset of inconsolable crying, abdominal pain or priapism
Initially asymptomatic or mild sting +/- erythema, progressing to severe pain around the bite site
Localised sweating and piloerection
Pain and swelling of regional lymph nodes
Nausea, vomiting and abdominal pain
Lethargy and malaise
Regional or generalised pain and sweating. Often fluctuating
Mild tachycardia and hypertension
A cold compress may offer some relief
A pressure immobilisation bandage is not recommended and may increase pain
Simple analgesia such as paracetamol or ibuprofen
Opiates such as intranasal fentanyl or oxycodone po may be required
Note: the aim is for a reduction in pain to acceptable levels, not a pain free state. Only 25% of patients have a reduction in pain 2 hours post bite and 50% at 24 hours.
Redback spider antivenom was historically given in cases of severe pain and systemic symptoms; however a recent RCT (RAVE II) has brought its effectiveness into question
All cases of redback spider envenomation should be discussed with a senior ED doctor and consider seeking input by the Duty Toxicologist at Poisons Information: 131126
In a monitored area with facilities to treat anaphylaxis readily available
Observations including BP should be done at baseline, 15 mins, 30 mins then hourly for 2 hours
Give 2 ampoules diluted in 10mL/kg (max 100mL) of 0.9% saline IV over 20 minutes
Dose of antivenom is not dependent on the age or weight of the child
The IV route is a safe and well-established practice despite the product information stating it is given via the IM route
Hypersensitivity reactions (<5%) are usually limited to a rash. Anaphylaxis is rare and should be managed by stopping the infusion and standard therapies – refer to Anaphylaxis
Serum sickness (< 10%) occurs 5-10 days post antivenom administration and presents with fever, rash, joint pains and myalgia. It responds well to 5 days of oral prednisolone.
No species are found in Western Australia
Other Spider Bites and “Necrotising Arachnidism”
Many spider bites may be associated with local irritation and inflammation and symptomatic treatment with analgesics and antihistamines for itch is generally all that is required.
The white-tailed spider (Lampona cylindrata) was long implicated in medical literature and media reports as causing skin necrosis and ulceration. Spider bite in Australia is an extremely uncommon cause of ulceration and should only be considered at the end of a long list of other differential diagnoses including infections and vasculitis. Prospective studies have failed to support the association between Australian spiders and such lesions. Even if a skin ulcer is thought to have been the result of a spider bite, treatment is symptomatic with analgesia, elevation and good wound care. Rarely, the input of a plastic surgeon may be required for wound debridement and skin grafting.
Isbister GK et al. A randomised controlled trial of intramuscular versus intravenous antivenom for latrodectism – the RAVE study. Quarterly Journal of Medicine 2008; 101:557-565
Isbister GK et al. Randomised controlled trial of intravenous antivenom versus placebo for lactrodectism: the second redback antivenom evaulation (RAVE II) study. Annals of Emergency Medicine 2014; 64:1-9.
Isbister GK, Gary MR. White-tailed spider: a prospective series of 130 definite bites by the Lampona species. Medical Journal of Australia 2003; 179:199-202
Murray L, Little M, Pascu O and Hoggett K. Toxicology Handbook. 3rd Edition. Chatswood, NSW: Elsevier Australia; 2015.
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