Polyvalent Snake Antivenom

Polyvalent antivenom (equine IgG Fab) is used to treat snake envenomation from Australia and Papua New Guinea snakes. It contains the equivalent of an ampoule of Brown, Tiger, Black, Death and Taipan in 50ml.

Indication:

• Clinical evidence of envenomation from an Australian or Papua New Guinea snake when the correct monovalent antivenom can not be identified or acquired.
• Not recommended in Tasmania (Tiger antivenom only) or in Victoria and South-West Western Australia (use a combination of Brown and Tiger snake antivenom)

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 1 ampoule diluted in 500ml of 0.9% saline IV over 20 minutes (the dose is the same for adults and paediatrics – snakes don’t envenomate less because its a child)
• Can be given as a rapid IV push if the patient is haemodynamically unstable or in cardiac arrest.

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.

Top Tips:

• It is unusual to need the Polyvalent antivenom even when the snake is unknown. Toxicologists use the combination of clinical features, laboratory results and geography to narrow the treatment down to one or two monovalent antivenins. The use of monovalent antivenoms reduces the risk of adverse outcome. If in doubt speak to your local toxicologist for advice.

References

• Isbister GK, Brown SG, MacDonald E et al. Current use of Australian snake antivenoms and frequency of immediate-type hypersensitivity reactions and anaphylaxis.  Medical Journal of Australia 2008; 188:473-476.
• White J. A clinician’s guide to Australian venomous bites and stings: Incorporating the updated CSL antivenom handbook. Melbourne: CSL Ltd, 2012.