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OBJECTIVE To test an equine-derived polyvalent viperid antivenom (EPVA) in the treatment of dogs with evidence of viper envenomation. DESIGN Prospective, multicenter observational study. SETTING Veterinary emergency and critical care hospitals. ANIMALS A total of 82 client-owned dogs with progressive clinical signs after viperid snakebite were enrolled in the study. INTERVENTIONS Equine-derived polyvalent viperid antivenom was administered at a dosage of 1 mL/kg body weight, either by IV infusion or SC injection. MEASUREMENTS AND MAIN RESULTS A standardized snakebite severity score (SSS) was used to characterize the severity of envenomation and the clinical course after EPVA treatment. Most dogs had improved SSS both at 4 (65.8%) and 8 hours (81.7%) following EPVA administration. Five dogs died. At the 4-week assessment, 3 dogs had slightly abnormal hematological or coagulation parameters; all other surviving dogs showed no abnormalities. Antivenom-related acute or intermediate reactions occurred in 12 dogs (14.6%). CONCLUSIONS In the first study on antivenom in dogs in Italy, the effects of progressive viper envenomation were stabilized or reversed in the large majority of dogs receiving EPVA, as confirmed by the SSS analyses.