Indication for and timing of antivenom administration

Antivenom is usually indicated if there is evidence of systemic envenoming (see Evidence of systemic envenoming from snake bite); however, early discussion with a clinical toxicologist or a poisons information centre (13 11 26) is strongly recommended when considering antivenom therapy.

If the decision is made to give antivenom, administer it as early as possible. Evidence supports early administration of antivenom within 2 hours of the bite. Early antivenom administration may prevent or limit complications, including neurotoxicity, myotoxicity and acute kidney injury.

The 2-hour window for administration of antivenom often occurs before investigation results are available, or before the patient is retrieved from a remote location. This means the decision to administer antivenom may need to be based on clinical evidence of systemic envenoming alone, which may only comprise nonspecific systemic symptoms (eg nausea, vomiting, headache, abdominal pain, diarrhoea, sweating)—seek advice from a clinical toxicologist or a poisons information centre.

In a patient with suspected snake bite, the following scenarios may warrant early administration of antivenom (within 2 hours of the bite) before laboratory results are available:

• nonspecific systemic symptoms, especially headache and vomiting
• systemically unwell appearance
• early cardiovascular collapse (eg hypotension, cardiac arrest, unconsciousness, seizures)
• ptosis or blurred vision.

There is no role for antivenom more than 12 hours after the snake bite because the risk of adverse reactions outweighs the minimal benefit of treatment at this time.