Venom recurrence or persistence in the circulation after antivenom treatment has been documented many times in viper envenoming. However, it has not been associated with clinical recurrence for many snakes, including Russell's viper (Daboia spp.). We compare the recovery of coagulopathy to the recurrence or persistence of venom in patients with Russell's viper envenoming.
The study included patients with Russell's viper (D. russelii) envenoming presenting over a 30 month period who had Russell's viper venom detected by enzyme immunoassay. Demographics, information on the snake bite, and clinical effects were collected for all patients. All patients had serum collected for venom specific enzyme immunoassay and citrate plasma to measure fibrinogen levels and prothrombin time (international normalised ratio; INR). Patients with venom recurrence/persistence were compared to those with no detectable recurrence of venom. There were 55 patients with confirmed Russell's viper envenoming and coagulopathy with low fibrinogen concentrations: 31 with venom recurrence/persistence, and 24 with no venom detected post-antivenom. Fibrinogen concentrations increased and INR decreased after antivenom in both the recurrence and non-recurrence patients. Clinical features, laboratory parameters, antivenom dose and length of hospital were similar for both groups. Pre-antivenom venom concentrations were higher in patients with venom recurrence/persistence with a median venom concentration of 385 ng/mL (16–1521 ng/mL) compared to 128 ng/mL (14–1492 ng/mL; p = 0.008).
Recurrence of Russell's viper venom was not associated with a recurrence of coagulopathy and length of hospital stay. Further work is required to determine if the detection of venom recurrence is due to the venom specific enzyme immunoassay detecting both venom-antivenom complexes as well as free venom.
Snakebite is a major public health problem and understanding the effectiveness of antivenom is essential to improving health outcomes. The measurement of venom in blood has been used to assess the effectiveness of antivenom. The absence of venom post-antivenom indicating that sufficient antivenom has been given, and the persistence or recurrence of venom indicating that insufficient antivenom has been given. There are numerous reports of venom recurrence with viper bites, including Russell's viper bites. However, it remains unclear if venom recurrence is always an indicator of inadequate antivenom and recurrence of clinical envenoming. In this study, we compare patients with and without the persistence or recurrence of venom who develop coagulopathy after Russell's viper bites. There was no difference in the recovery of the coagulopathy between the two groups of patients demonstrating that for Russell's viper envenoming, venom recurrence or persistence was not associated with the recurrence or persistence of clinical effects such as coagulopathy. Patients with detectable venom after antivenom did have higher pre-antivenom venom concentrations. Further investigation is required to interpret venom concentrations post-antivenom.