Recurrent neurotoxic envenoming of cobra bite

Abstract

Recurrent systemic envenomation in patients who sustained viper bites, and who previously responded to antivenom, is well described in the literature. However, cases of recurrent neurotoxic envenoming after antivenom treatment are rarely reported. We present three patients who were envenomed by a cobra (Naja kaouthia or N. siamensis) and experienced recurrent neurotoxic envenomation after they initially responded to antivenom treatments. These three patients, aged 13, 35 and 65 years, were consulted to the Ramathibodi Poison Centre. All were bitten by cobra snakes and developed neurotoxic signs and symptoms including ptosis, muscle weakness, and respiratory failure. All were treated with, and responded to, Fragment Affinity-Purified Secondary Antibody [F(ab')₂] antivenom. Two cases underwent debridement and fasciotomy. One case required extensive wound dressing with bleb aspiration, in addition to usual wound care. Approximately 6-14 hours after these procedures, all three patients developed recurrent signs and symptoms of neurotoxicity. All received second doses of antivenom, after which their symptoms improved, and all were ultimately discharged. Each of these cases exhibited recurrent systemic envenomation that resulted from cobra bites after they exhibited antivenom responses. We believe that non-neutralized venom that remained at the bite site, was released, and re-entered the circulation after the wound was manipulated or the patient underwent surgery. This may explain these instances of recurrent envenomation. Future investigations should examine other potential mechanisms of recurrent envenomation, especially in patients without histories of aggressive wound manipulation. If neurological effects recur, prompt re-treatment with antivenom should be considered.

Keywords: Cobra; Envenomation; Neurotoxic snakes; Recurrent; Snakebite.