Cefalonium Products | Cleanchem - Cefalonium is a third-generation cephalosporin antibiotic used to treat bacterial infections in animals, especially in veterinary medicine. It works by inhibiting bacterial cell wall synthesis, making it effective against both gram-positive and gram-negative organisms. Cefalonium is used primarily in veterinary practices for treating infections in cattle and poultry. Side effects in animals may include mild gastrointestinal upset and allergic reactions.