Advantages of Listerine and Peroxide
Hydrogen peroxide that is sold for medical purposes like first aid is good to have on hand for basic animal first aid, including cuts or scrapes that may become infected, because hydrogen peroxide acts as an antiseptic, preventing infection.
The mouthwash product Listerine was originally created as a surgical antiseptic for sterilizing. Older bottles of the original, yellow Listerine said it was fine for treating minor cuts and abrasions, until it was marketed as a mouthwash.
Disadvantages of Listerine and Peroxide
The alcohol in Listerine can dry out a dog's ear, making the problem worse. Hydrogen peroxide bubbles can frighten a dog when placed in the ear, and both products may not reach or kill all of the bacteria causing an ear infection. Neither product acts as an anti-inflammatory drug, which along with antibiotics is a common treatment for ear infections in dogs.
An ear infection usually needs to be treated with antibiotics. Peroxide can be used to clean the outside of a dog's ears, but not the inside of any pet's ears. In any case, with these products it would be difficult to reach any bacteria inside of the dog's ear that needs to be killed. Peroxide is better for cleaning outside or around an infected ear than Listerine, but it is not an effective treatment to cure an infection. Furthermore, liquids should not be inserted into a dog's ear without veterinary supervision.