Cephapirin Products | Cleanchem - Cephapirin is a first-generation cephalosporin antibiotic primarily used to treat skin and soft tissue infections caused by gram-positive bacteria. It works by interfering with the synthesis of the bacterial cell wall, leading to cell death. Cephapirin is often used in veterinary medicine for treating mastitis in dairy cows. Side effects in humans are rare but can include gastrointestinal upset and allergic reactions.