Antibiotics in the penicillin class disrupt the bacterial cell wall. These tend to be broad-spectrum antibiotics, except when they encounter bacteria that have a specific resistance. Amoxicillin is a type of penicillin used in dogs, and frequently is prescribed because it's well-absorbed in the gut. It's more effective when paired with clavulanic acid, known more commonly as clavamox. Clavamox has a broader spectrum than amoxicillin, and is helpful for taking on Staphlylococcal infections, usually associated with skin infections.
The 'killer app' for canine itching and skin infections - SFGate
The most common (and acceptable) use of non-prescription antibiotics is for topical application for minor cuts, skin irritations or ear and eye infections. Most human OTC remedies are safe and effective for dogs. Creams such as neomycin, bacitracin, and mycitracin and other triple antibiotic ointment are safe, effective and readily available. Several safe OTC ear and eye ointments are available at pet stores or veterinary supply merchants.
Bacterial Skin Infection DOGS - Animal Hospital of Montgomery
Most dogs at some point in their lives will need antibiotic treatment for internal or external diseases and infections. Many owners will try to forego a trip to the veterinarian by trying to fight an infection with over-the-counter (OTC) or non-prescription antibiotics. For anything more than a minor skin, ear, or eye infection, treating with an OTC antibiotic is not recommended.
Canine Pyoderma (Pus in the skin) or Bacterial Skin Infection ..