Clinical Efficacy and Pharmacokinetics of Antivenom Viperfav® in Vipera ammodytes ammodytes Envenomation

<b>Background:</b> In Europe, <i>Vipera ammodytes ammodytes</i> (<i>Vaa</i>, nose-horned viper) is considered the most venomous of the European vipers. The antivenom Viperfav^®, composed of polyvalent equine F(ab')₂ fragments, is effective against <i>Vipera aspis</i>, <i>Vipera berus</i> and <i>Vaa</i>. <b>Objectives</b>: This study aimed to evaluate the clinical efficacy and pharmacokinetics of Viperfav in <i>Vaa</i> envenomations. <b>Methods:</b> Patients presenting with <i>Vaa</i> snakebite and treated with intravenous Viperfav were included. Clinical manifestations and laboratory findings were assessed on admission to the Emergency Department, prior to antivenom therapy, and monitored throughout hospitalization. Blood samples were collected on arrival and at defined intervals after Viperfav administration. Venom and antivenom concentrations in serum were determined by ELISA and subjected to pharmacokinetic analysis. <b>Results:</b> Twenty-one patients bitten by <i>Vaa</i> and classified with a severity score of 2b on the modified Audebert clinical severity scale received a single intravenous dose of Viperfav within 4 h of the bite. Viperfav attenuated the progression of local symptoms and prevented the development of new systemic manifestations. The serum concentrations of F(ab')₂ fragments reached 196 µg/mL, far exceeding the venom concentration at admission (35 ng/mL). The prolonged elimination half-life of Viperfav (49 h) corresponded with the absence of recurrent symptoms after a single dose. Bradycardia or hypotension occurred in 10% of patients; no cases of anaphylaxis or serum sickness were observed. <b>Conclusions:</b> A single intravenous dose of Viperfav demonstrated clinical efficacy and a favourable pharmacokinetic profile in <i>Vaa</i> envenomed patients when administered within hours of the bite.