What is the recommended procedure for intravenously administering octaplex (polyvalent Australian snake antivenom) in a patient with suspected venomous Australian snake bite and systemic envenoming?

Administration of Octaplex (Polyvalent Australian Snake Antivenom)

Immediate Pre-Administration Steps

For suspected Australian snake envenoming with systemic effects, establish intravenous access immediately and prepare to administer one vial of the appropriate antivenom as soon as envenoming is confirmed. 1, 2

Patient Preparation and Assessment

• Admit all patients with suspected snakebite to a hospital with onsite laboratory facilities and appropriate antivenom stocks for at least 12 hours of observation, even if initially appearing well 1
• Establish IV access before antivenom administration 3
• Ensure airway management equipment and ventilatory support are immediately available, particularly for neurotoxic envenomations 4, 3
• Have resuscitation equipment ready for potential anaphylaxis, as 24% of antivenom recipients experience systemic hypersensitivity reactions (6% severe) 2

Confirming Envenoming Before Administration

Do not administer antivenom without evidence of systemic envenoming, as most snakebites do not result in significant envenoming 1. Evidence includes:

• Venom-induced consumption coagulopathy (most common - 73% of envenomed patients) 1, 2
• Myotoxicity (17% of cases) 2
• Neurotoxicity (ptosis, glossopharyngeal palsy) 5
• Sudden collapse 1
• Thrombotic microangiopathy or renal impairment 1
• Abnormal bleeding or non-clotting blood 5

Serial Monitoring Protocol

• Perform serial blood testing: activated partial thromboplastin time (aPTT), international normalized ratio (INR), and creatine kinase (CK) levels 1
• Conduct serial neurological examinations 1
• Continue monitoring for at least 12 hours, as neurotoxicity onset can be delayed up to 13 hours despite minimal local findings 6

Antivenom Administration Protocol

Dosing

One vial of the relevant antivenom is sufficient to bind all circulating venom 1. The median antivenom dose has declined from four vials to one vial without harming patients 2.

• For polyvalent (Octaplex) antivenom when snake type is unclear: administer one vial 1
• Alternatively, if geographical distribution narrows possibilities, two monovalent antivenoms (e.g., brown snake and tiger snake) can be used instead of polyvalent 1

Route of Administration

Intravenous infusion is mandatory for effective antivenom treatment 5. Do not administer by any other route.

Timing Considerations

• Administer antivenom as soon as evidence of envenoming is confirmed 1
• Critical pitfall: The median time to first antivenom in Australian practice is 4.3 hours (IQR 2.7-6.3 hours), which represents a significant delay 2
• Early antivenom therapy is associated with lower peak creatine kinase in myotoxic envenomations 7

Managing Antivenom Reactions

Hypersensitivity Risk

• 24% of antivenom recipients experience systemic hypersensitivity reactions; 6% are severe (hypotension, hypoxemia) 2
• Have epinephrine, antihistamines, and corticosteroids immediately available 5
• Monitor continuously during infusion and for 30 minutes post-administration 8

Reaction Management

• For anaphylaxis: stop infusion, administer epinephrine, provide fluid resuscitation and ventilatory support as needed 5
• After stabilization, antivenom can often be restarted at a slower rate if envenoming is life-threatening 5

Post-Administration Monitoring

Expected Recovery Timeline

• Recovery may be delayed as many clinical and laboratory effects of venom are not immediately reversible 1
• Coagulopathy typically resolves over hours to days 2
• Myotoxicity can be severe (peak CK >48,000 U/L) with rapid onset (time to peak 13-15 hours) 7

Continued Observation

• Continue serial blood tests until coagulopathy resolves 1
• Monitor for acute kidney injury (occurs in 12% of envenomed patients) 2
• Watch for delayed complications including major hemorrhage (1.6% of cases) or cardiac arrest (2.9% of cases) 2

Critical Pitfalls to Avoid

• Do not rely on Snake Venom Detection Kit (SVDK) results alone: 4.9% were incorrect for envenomed patients, and 36% were false positives in non-envenomed patients 2
• Do not assume absence of envenoming based on minimal local findings: neurotoxic bites cause life-threatening systemic toxicity despite minimal local injury 6
• Do not administer antivenom to non-envenomed patients: 49 non-envenomed patients received unnecessary antivenom in the Australian Snakebite Project, with 10 experiencing hypersensitivity reactions 2
• Do not delay antivenom while waiting for definitive snake identification: use polyvalent antivenom or two appropriate monovalent antivenoms based on geographical distribution 1

Adjunctive Therapies

• Analgesics for pain management 9
• Fluid therapy for hypotension 9
• Hemodialysis for renal impairment 9
• Antibiotic therapy if wound infection develops 9
• Ventilator support for respiratory failure from neurotoxic envenoming 9