Abstract:
Coastal taipan (Oxyuranus scutellatus) envenoming causes life-threatening neuromuscular
paralysis in humans. We studied the time period during which antivenom remains effective in
preventing and arresting in vitro neuromuscular block caused by taipan venom and taipoxin. Venom
showed predominant pre-synaptic neurotoxicity at 3 µg/mL and post-synaptic neurotoxicity at 10
µg/mL. Pre-synaptic neurotoxicity was prevented by addition of Australian polyvalent antivenom
before the venom and taipoxin and, reversed when antivenom was added 5 min after venom and
taipoxin. Antivenom only partially reversed the neurotoxicity when added 15 min after venom and
had no significant effect when added 30 min after venom. In contrast, post-synaptic activity was fully
reversed when antivenom was added 30 min after venom. The effect of antivenom on pre-synaptic
neuromuscular block was reproduced by washing the bath at similar time intervals for 3 µg/mL,
but not for 10 µg/mL. We found an approximate 10–15 min time window in which antivenom can
prevent pre-synaptic neuromuscular block. The time window is likely to be longer in envenomed
patients due to the delay in venom absorption. Similar effectiveness of antivenom and washing with
3 µg/mL venom suggests that antivenom most likely acts by neutralizing pre-synaptic toxins before
they interfere with neurotransmission inside the motor nerve terminals.
