The correct dose of penicillin for dogs varies based on the type of penicillin prescribed. For example, dogs given amoxicillin as a shot in the muscle should get 4 to 10 milligrams per kilogram of body weight, once or twice daily, states The Merck Veterinary Manual.
Dogs receiving amoxicillin orally should get 10 to 20 milligrams per kilogram of body weight, once per day, states Merck Manuals.
Penicillin is distributed by prescription only, states petMD. Some dogs might experience an allergic reaction to penicillin or experience a loss of appetite, vomiting, diarrhea or joint pain. Some bacteria are resistant to penicillin, so another antibiotic may be necessary to clear an infection.