Antivenom therapy is currently the standard practice for treating neuromuscular dysfunction in snake envenoming. We reviewed the clinical and experimental evidence-base for the efficacy and effectiveness of antivenom in snakebite neurotoxicity. The main site of snake neurotoxins is the neuromuscular junction, and the majority are either: (1) pre-synaptic neurotoxins irreversibly damaging the presynaptic terminal; or (2) post-synaptic neurotoxins that bind to the nicotinic acetylcholine receptor. Pre-clinical tests of antivenom efficacy for neurotoxicity include rodent lethality tests, which are problematic, and in vitro pharmacological tests such as nerve-muscle preparation studies, that appear to provide more clinically meaningful information. We searched MEDLINE (from 1946) and EMBASE (from 1947) until March 2017 for clinical studies. The search yielded no randomised placebo-controlled trials of antivenom for neuromuscular dysfunction. There were several randomised and non-randomised comparative trials that compared two or more doses of the same or different antivenom, and numerous cohort studies and case reports. The majority of studies available had deficiencies including poor case definition, poor study design, small sample size or no objective measures of paralysis. A number of studies demonstrated the efficacy of antivenom in human envenoming by clearing circulating venom. Studies of snakes with primarily pre-synaptic neurotoxins, such as kraits (Bungarus spp.) and taipans (Oxyuranus spp.) suggest that antivenom does not reverse established neurotoxicity, but early administration may be associated with decreased severity or prevent neurotoxicity. Small studies of snakes with mainly post-synaptic neurotoxins, including some cobra species (Naja spp.), provide preliminary evidence that neurotoxicity may be reversed with antivenom, but placebo controlled studies with objective outcome measures are required to confirm this. Full article

There is limited information on the cross-neutralisation of neurotoxic venoms with antivenoms. Cross-neutralisation of the in vitro neurotoxicity of four Asian and four Australian snake venoms, four post-synaptic neurotoxins (α-bungarotoxin, α-elapitoxin-Nk2a, α-elapitoxin-Ppr1 and α-scutoxin; 100 nM) and one pre-synaptic neurotoxin (taipoxin; 100 nM) was studied with five antivenoms: Thai cobra antivenom (TCAV), death adder antivenom (DAAV), Thai neuro polyvalent antivenom (TNPAV), Indian Polyvalent antivenom (IPAV) and Australian polyvalent antivenom (APAV). The chick biventer cervicis nerve-muscle preparation was used for this study. Antivenom was added to the organ bath 20 min prior to venom. Pre- and post-synaptic neurotoxicity of Bungarus caeruleus and Bungarus fasciatus venoms was neutralised by all antivenoms except TCAV, which did not neutralise pre-synaptic activity. Post-synaptic neurotoxicity of Ophiophagus hannah was neutralised by all antivenoms, and Naja kaouthia by all antivenoms except IPAV. Pre- and post-synaptic neurotoxicity of Notechis scutatus was neutralised by all antivenoms, except TCAV, which only partially neutralised pre-synaptic activity. Pre- and post-synaptic neurotoxicity of Oxyuranus scutellatus was neutralised by TNPAV and APAV, but TCAV and IPAV only neutralised post-synaptic neurotoxicity. Post-synaptic neurotoxicity of Acanthophis antarcticus was neutralised by all antivenoms except IPAV. Pseudonaja textillis post-synaptic neurotoxicity was only neutralised by APAV. The α-neurotoxins were neutralised by TNPAV and APAV, and taipoxin by all antivenoms except IPAV. Antivenoms raised against venoms with post-synaptic neurotoxic activity (TCAV) cross-neutralised the post-synaptic activity of multiple snake venoms. Antivenoms raised against pre- and post-synaptic neurotoxic venoms (TNPAV, IPAV, APAV) cross-neutralised both activities of Asian and Australian venoms. While acknowledging the limitations of adding antivenom prior to venom in an in vitro preparation, cross-neutralization of neurotoxicity means that antivenoms from one region may be effective in other regions which do not have effective antivenoms. TCAV only neutralized post-synaptic neurotoxicity and is potentially useful in distinguishing pre-synaptic and post-synaptic effects in the chick biventer cervicis preparation. Full article

Venom detection is crucial for confirmation of envenomation and snake type in snake-bite patients. Enzyme immunoassay (EIA) is used to detect venom, but antivenom in samples prevents venom detection. We aimed to detect snake venom in post-antivenom samples after dissociating venom-antivenom complexes with glycine-HCl (pH 2.2) and heating for 30 min at 950 °C. Serum samples underwent dissociation treatment and then Russell’s viper venom or Australian elapid venom measured by EIA. In confirmed Russell’s viper bites with venom detected pre-antivenom (positive controls), no venom was detected in untreated post-antivenom samples, but was after dissociation treatment. In 104 non-envenomed patients (negative controls), no venom was detected after dissociation treatment. In suspected Russell’s viper bites, ten patients with no pre-antivenom samples had venom detected in post-antivenom samples after dissociation treatment. In 20 patients with no venom detected pre-antivenom, 13 had venom detected post-antivenom after dissociation treatment. In another 85 suspected Russell’s viper bites with no venom detected pre-antivenom, 50 had venom detected after dissociation treatment. Dissociation treatment was also successful for Australian snake envenomation including taipan, mulga, tiger snake and brown snake. Snake venom can be detected by EIA in post-antivenom samples after dissociation treatment allowing confirmation of diagnosis of envenomation post-antivenom. Full article