Credelio requires a prescription from your veterinarian and is available for dogs and puppies 4.4-6.0 lbs (56.25 mg), 6.1-12.0 lbs (112.5 mg), 12.1-25.0 lbs (225 mg), 25.1-50.0 lbs (450 mg), and 50.1-100 lbs (450 mg X 2).