IM21.7 | Snake Bite Antivenom Therapy — Summary & Reflection

KEY TAKEAWAYS

Anti-snake venom (ASV) is the only definitive treatment for systemic snakebite envenomation. Indian polyvalent ASV is raised against all big four species — give it regardless of which species is suspected when an indication is present.

Indications: Positive 20WBCT, spontaneous systemic bleeding, any neurotoxic sign (ptosis onwards), haemodynamic instability, AKI from envenomation. NOT local swelling alone.

Mechanism: Equine IgG antibodies neutralise circulating (unbound) venom; cannot remove already-tissue-bound toxin. Antivenom arrests progression — it does not instantly reverse established paralysis or instantly restore depleted clotting factors.

Dose and route: 10 vials IV (same dose adults and children); dilute in 100–500 mL normal saline; start slowly (15 min), complete over 60–90 min; adrenaline 0.5 mg drawn up BEFORE starting.

Adverse reactions: Early (anaphylactoid/anaphylaxis): STOP infusion → adrenaline 0.5 mg IM anterolateral thigh → IV fluids → hydrocortisone 200 mg + chlorphenamine 10 mg → restart slowly. Late (serum sickness 5–14 days): prednisolone 1 mg/kg × 5–7 days.

Response assessment: 20WBCT at 6 hours post-antivenom. Still positive → repeat 10 vials. Blood products (FFP) only after antivenom, not before.

Neostigmine + atropine for cobra (post-synaptic) neurotoxicity: 1.5 mg neostigmine + 0.6 mg atropine IV — always together; may partially reverse cobra block; ineffective for krait (pre-synaptic).

REFLECT

Reflect on the hook scenario: the three questions the nurse asked — how many vials, how fast, and what if the patient wheezes — are the exact questions this module answers. Think about the last time you were in an emergency situation and did not know a drug dose. How did that uncertainty affect your ability to act decisively? The antivenom protocol is not complicated, but it must be memorised so completely that it can be executed under pressure, in a poorly lit primary health centre, with a hypotensive patient and an anxious family watching. The protocol is: confirm indication → draw up adrenaline → 10 vials IV over 60–90 minutes starting slowly → watch continuously → if reaction: stop, adrenaline IM → assess at 6 hours → repeat if still positive. Write that sequence from memory three times. Then you own it.