First Clinical Report on Efficacy of Alternative European Viper Antivenoms in Treatment of Vipera ammodytes Envenomation in Croatia

In Croatia, the European Viper Venom Antiserum®, produced by the Institute of Immunology Zagreb, was the only antiserum used to treat Vipera ammodytes envenomation. When production of the Zagreb antivenom ceased, three other antivenoms, Viperfav®, BulBio®, and Viekvin®, replaced it in clinical practice at the Department of Infectious Diseases, University Hospital Split. This study includes 34 patients envenomed by Vipera ammodytes during the period between 2020 and 2025: 24 (71%) suffered grade 2a envenomation, nine (26%) grade 2b, and one grade 3 (severe envenomation). None were admitted to the Intensive Care Unit. All patients received antivenom: 16 received Viperfav®, 17 BulBio®, and one Viekvin®. All grade 2a patients were treated with a single dose of antivenom. Among grade 2b patients, four received one dose and two received two doses of Viperfav®, while one received one dose and two received two doses of BulBio®. The grade 3 patient received two doses of BulBio®. In all cases, treatment was successful and patients were discharged from hospital after an average of 3.97 days. Patients with pronounced neurotoxic signs did not require treatment with multiple doses of antivenom. All antivenoms proved effective. No adverse reactions or fatalities were observed.