A prospective observational phase IV study on effectiveness of animal derived polyclonal antibody antivenoms against West African carpet viper (Echis romani) induced coagulopathy and mortality.

Conventional polyclonal antibody antivenoms are the mainstay of snakebite therapy. They have not been proven to be efficacious in randomized placebo controlled clinical trials among severely envenomed patients. There is also paucity of evidence on effectiveness especially in routine use. The current study evaluated their effectiveness in post marketing use among those managed with and without antivenom as regards to reversal of venom induced coagulopathy defined using the 20 min Whole Blood Clotting Test [20WBCT] and in averting death. The effectiveness of antivenom was evaluated among 5467 patients predominantly envenomed by the West African carpet viper (Echis romani) at 3 hospitals in Nigeria from 2021 to 2022. Two antivenoms Echitab G (EG) and Echitab ICP Plus (EP) were able to restore normal clotting within 6 h of administration in 58.0% [95% Confidence Interval (95%CI)] (95%CI:51.2-64.5%) and 91.7% (95%CI:90.4-93.0%) of patients respectively. They were able to restore normal clotting within 24 h of administration in 96.9% (95%CI:94.0-98.7%) and 99.0% (95%CI:98.4-99.4%) of patients respectively. The Odds Ratio [OR (95%CI)] of dying among patients with positive 20WBCT who were treated with ≥1 vial of either EG or EP compared to those not treated was 0.06 (0.02-0.23) and 0.07 (0.03-0.15) respectively. This equated to antivenom protection against in-hospital mortality of 93-94% among patients with confirmed coagulopathy though the benefit appeared abrogated among those without coagulopathy. The untreated natural mortality was 15.94% (95%CI:8.24-26.74%) without antivenom therapy while the overall mortality was 84/5105 (1.65%; 95%CI:1.32-2.03%. The Number Needed to Treat (NNT) to avert a death was 7 patients among patients with coagulopathy. Antivenoms were safe with mild early adverse reactions observed among 2.6% (95%CI:2.13-3.08%) of antivenom recipients. Polyclonal antibody antivenoms are effective and safe for treating coagulopathic envenomed patients in Nigeria.