Ampicillin injection is administered parenterally, preferably for severe or moderately severe infections in animals. The dosage and frequency depend on the animal's weight, the type and severity of the infection, and the animal's kidney function. For example, in dogs, the recommended dosage is 22 mg/kg every 6 to 8 hours for severe infections and every 12 hours for less severe infections. In cats, the dosage is 50 mg/kg every 6 to 8 hours. It is essential to follow the manufacturer's instructions and consult with a veterinarian for the appropriate dosage and administration guidelines for each animal species and individual case.