Redback Spider Antivenom

Redback Spider Antivenom (equine IgG Fab) can be used to treat envenomation from Australian Redback spider.

Indication:

• Clinical evidence of systemic envenomation e.g. latrodectism
• Severe localised pain unrelieved by opiate analgesia

Contraindication:

• No absolute
• Increased Risk of anaphylaxis in patients previously treated with antivenom or those who are suspected of equine sera allergy

Administration:

• Place the patient in a monitored area where anaphylaxis can be managed.
• Administer 2 ampoules diluted in 100ml of 0.9% saline and administered intravenous over 20 minutes.
• Adult and paediatric doses are the same.

Adverse drug reactions:

• Anaphylaxis: Cease antivenom infusion, treat as per anaphylaxis with oxygen, IV fluids and IM adrenaline. Recommence antivenom infusion when anaphylaxis has resolved. Rarely will ongoing administration of adrenaline be required to complete the antivenom infusion.
• Serum Sickness: A benign and self limiting complication occurs 5-10 days after antivenom, symptoms include fever, rash, arthralgia and myalgia. Oral steroids for 5 days may ameliorate symptoms (e.g. prednisolone 50mg/day in adults and 1mg/kg in children). All patients should be warned about this complication who receive antivenom.

Controversies:

• Redback antivenom has gone in and out of favour over the years between initial thoughts that it was effective then IM was ineffective. Recently a trial (RAVE II) would suggest that there is no benefit to IV antivenom administration over simple analgesia. However, many toxicologists have seen examples of patients with severe laterdectism respond to antivenom and it will be virtually impossible to create a trial based on these extreme cases.

References

• Tox Library – Redback Spider
• Redback Spider Envenoming
• Isbister GK, Brown SGA, Miller M et al. A randomised controlled trial of intramuscular versus intravenous antivenom for lactrodectism – the RAVE study. Quarterly Journal of Medicine 2008; 101:557-565.
• Isbister GK, O’Leary MA, Miller M et al. A comparison of serum antivenom concentrations after intravenous and intramuscular administration of redback (widow) spider antivenom. British Journal of Clinical Pharmacology 2008; 65:138-143.
• Isbister GK. Safety of i.v. administration of redback spider antivenom. Internal Medicine Journal 2007; 37:820-822.
• Isbister GK et al. Randomised controlled trial of intravenous antivenom versus placebo for lactrodectism: the second redneck antivenom evaluation (RAVE II) study. Annals of Emergency Medicine 2014; 64:1-9