Sydney funnel web spider bites (Atraxis)

Introduction

Australian funnel-web spiders belong to two genera of the family Hexathelidae: Hadronyche and Atrax.
They are medium to large spiders; generally black to brown, they will often raise up their front legs if threatened to display their prominent chelicerae with large parallel fangs.
They are distributed down the eastern seaboard of Australia and into Tasmania.
The only proven killer, is the Sydney funnel web spider (Atrax robustus), which is potentially one of the most lethal of the venomous animals in the world and is believed to be confined to a 260km radius surrounding the centre of the city of Sydney.
- Bites in Victoria are likely to only occur in spider collectors or accidental freight transport.
- Although toxicity may be rapid in onset, asymptomatic patients must be observed for at least four hours after the first aid has been removed, before a final decision to omit antivenom can be made. Most bites do not result in systemic envenomation but should always be treated as potentially life threatening.
The Victorian Funnel Web spider (found in the Dandenong Ranges), and several other funnel web and mouse spiders are found through Eastern Victoria and may be confused with the Sydney funnel web.
- They may cause bite-site pain, headaches, and nausea, but require no specific treatment.

The antivenom is a purified immunoglobulin prepared from the plasma of immune rabbits. It contains antibodies against the toxin components of the Sydney funnel web (Atrax robustus). These antibodies bind to the toxin inhibiting its effects.
The antivenom also has effect against the toxins of other funnel webs of the Hadronyche genus.
No deaths have been reported since the introduction of the antivenom.
Each vial contains 125 units of antivenom as a freeze-dried preparation. Until the time of reconstitution and use the antivenom should remain refrigerated at 2-8oC. Do not freeze. Protect from light.

evidence of systemic envenomation such as:
- Autonomic features: sweating, salivation, piloerection, lacrimation, and pupillary changes.
- Neurological features: headache, nausea, peri-oral paresthesia, muscle fasciculation and spasm, altered consciousness and coma.
- Cardiovascular features: hypertension and tachycardia, although hypotension and bradycardia may occur.
- Pulmonary oedema may also occur but appears to be non-cardiogenic.
NB. progression of severe envenomation leads to hypotension, hypoventilation and apnoea, continuing acute non-cardiogenic pulmonary oedema, coma, and eventually cardiac arrest.

many hospitals, especially those not in NSW, do NOT store funnel web antivenom and this will need to be sourced via the local toxinology service, in Victoria, contact the Victorian Poisons Information Centre on 13 11 26.

The total dose of antivenom should be reconstituted into 100mL of Normal Saline or Hartmann’s (10mL/kg in paediatric patients). Gently swirl until completely dissolved, which may take up to 10 minutes.
Once the powder is completed dissolved the product should be administered immediately.
Administer the required dose by slow IV injection, over 2 to 5 minutes.
It should be used as soon as possible after reconstitution. It must not be stored reconstituted
Anaphylaxis/anaphylactoid reactions may occur, thus resuscitation equipment including adrenaline should be at hand before administration. Premedication is not indicated.

Anaphylaxis
- The antivenom is an animal protein and thus anaphylaxis/anaphylactoid reactions are possible. There have been no reported reactions with the use of funnel web antivenom (it has only been used in a relatively low number of cases). Care should be taken in those with an atopic history or with a history of previous use of this antivenom.
Serum sickness
- Only one case has been reported and the routine use of steroids for serum sickness prophylaxis is not recommended for this antivenom. Advise patient of the symptoms and warn them/carer to seek urgent medical attention if symptoms develop.
blood-borne infection
- There is a theoretical risk of cross-species (rabbit to human) transmission of infective agents as this is a blood-derived product. There have been no such cases reported.

administer antivenom
- usually initial dose is 2 ampoules IV
  - for repeat doses, give one (1) ampoule IV every fifteen minutes until clinical improvement (up to 8 may be required. Use of up to 20 ampoules have been reported).
- if life-threatening envenomation (paralysis, coma, haemodynamic instability, APO, cardiac arrest), give four (4) ampoules IV.
supportive care of systemic features
- Hypotension & bradycardia – IV fluids, inotropic agents, atropine
- Pulmonary oedema – O2, NIV, intubation
- Paralysis, apnoea, or coma – intubation / mechanical ventilation
disposition
- the patient should be admitted to ICU/HDU for at least 24 hours if antivenom has been used. There is a risk of late onset pulmonary oedema.
- consider transfer of paediatric patients to a HDU/PICU.

remove pressure bandage once:
- patient has been clinically assessed, and,
- there is no evidence of systemic envenomation, and,
- IV access placed (at least 18G preferable), and,
- antivenom is available, and,
- resus equipment available, and,
- advice from a senior ED doctor or toxinologist
observe for at least 4 hours after removal of bandage
- avoid discharges overnight