A patient presents with ptosis, blurred vision, descending paralysis, and respiratory failure after a snake bite. The snake responsible most likely belongs to which family, and what is the primary toxin mechanism?

• A Viperidae — prothrombin activation causing consumptive coagulopathy
• B Elapidae — post-synaptic alpha-neurotoxins competitively blocking nicotinic acetylcholine receptors at the NMJ ✓
• C Colubridae — rear-fanged haemotoxin causing intravascular haemolysis
• D Hydrophiidae — myotoxin causing rhabdomyolysis without neurological features

Explanation

The descending paralytic syndrome (ptosis → ophthalmoplegia → bulbar → respiratory) is characteristic of Elapid envenomation (cobras, kraits, mambas). Alpha-neurotoxins (e.g., alpha-bungarotoxin, cobratoxin) are competitive antagonists at the nicotinic acetylcholine receptor (nAChR) at the NMJ, blocking neurotransmission without depolarisation. Beta-bungarotoxin additionally inhibits presynaptic ACh release. Vipers primarily cause coagulopathy. Sea snakes (Hydrophiidae) cause myotoxicity. Anti-venom is specific; neostigmine is partially effective for post-synaptic blockade.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.