Vipera ammodytes bites treated with antivenom ViperaTAb: a case series with pharmacokinetic evaluation.

CONTEXT: In clinical practice it is difficult to differentiate between V. berus and V. ammodytes venomous bites. In the past this was not a concern, but due to the current shortage in Viperfav™ and European viper venom antiserum availability, V. a. ammodytes venomous bites have recently been treated with ViperaTAb®, which is a pharmaceutical formulation containing a monospecific ovine Fab fragments against the venom of V. berus. OBJECTIVE: To evaluate ViperaTAb® in V. a. ammodytes envenomations. MATERIALS AND METHODS: This is a prospective case series of three consecutive patients envenomed by V. a. ammodytes snakebite treated with ViperaTAb®. V. ammodytes venom, neurotoxic ammodytoxins, and Fab fragment levels were determined in serum samples and a pharmacokinetic analysis of the antivenom Fab fragments was carried out. RESULTS: Three patients bitten by V. a. ammodytes with extensive local swelling, neurological symptoms and recurrent thrombocytopenia were treated with ViperaTAb®. V. ammodytes venom was detected in serum of all three patients. Ammodytoxins were detected in the serum of only the most severely envenomed patient who developed neurological symptoms. In the presented moderate cases, a dose of 8 mL of ViperaTAb® reduced swelling and improved systemic effects, such as thrombocytopenia. However, this dose of ViperaTAb® was not effective in the most severely envenomed patient with the highest serum values of V. ammodytes venom. In this case ViperaTAb® did not stop local swelling and it had no effect on neurological signs. ViperaTAb®'s systemic clearance, distribution and elimination half-lives were 4.3-13.4 mL/h/kg, 1.2-3.2 h and 14.1-55.4 h, respectively. CONCLUSIONS: In patients envenomed by V. a. ammodytes venom, ViperaTAb® reduces moderate swelling and temporarily improves systemic effects, except neurological symptoms. ViperaTAb® application induces a decrement of V. ammodytes venom level in the blood, but did not affect serum concentration of neurotoxic ammodytoxins in the one patient with measurable concentrations.