Ear infections used to be my nemisis when i was in private practice. They used to also seriously piss me off because so many veterinarians and owners mismanage and DO NOT treat them appropriately.
I think I've posted this before, but I honestly can't remember.
The first step is to identify what the causitive agent of the infection is: dogs get one of 3 types of infections in their ears: 1) bacteria, 2) yeast, 3) mixed bacteria and yeast infections.
To identify these organisms, the veterinarian needs to start with examining the ear with the otoscope and then needs to make a slide of the material within the ear and examine it under the microscope. IF THE VET DOESN'T LOOK AT WHAT IS GROWING IN THE EAR UNDER THE MICROSCOPE, THEY DONT KNOW WHAT THE HELL THEY ARE TREATING. because of this, a microscopic examination should be expected and if its not performed, consider finding a different veterinarian.
Bacterial infections are usually one specific type of bacteria that has gotten out of control. Mixed bacterial infections (meaning mulitiple types of baceteria) are generally more difficult to treat and often associated with chronic infections and may or may not have drug resistance issues. Typically ear infections are gram positive cocci (staph or strep type infections) or less commonly gram negative rods (e coli type orgainsms). For whatever reason, probably the increased moisture of the ear, dogs with floppy ears seemed to have more gram negative infections. I don't know why and this isn't some scientific fact, its just an observation from when I was seeing alot of dog ear infections. Ears with bacterial infections typically seem to be much more painful than yeast infections.
Yeast are often associated with allergies or swimming---basically anything taht causes a mild inflammation of the ear canal with moisture, the perfect environment for yeast to grow. Typically this is malazzezia type yeast that look like little snowmen under a microscope with a diff-quick type stain. Ears with yeast infections tend to be EXTREMELY itchy.
Mixed bacterial/yeast infections are more difficult to treat and can require multiple drugs (antibiotics + antifungals + antinflammatories) and often require weeks of treatment.
So the first step for the veterinarian is to take a sample of the waxy material from the ear and look at it under the microscope. The slides made should at least be stained with a diff-quick type wrights stain and then possibly a gram stain to identify properties of specific bacteria. The gram stain will guide the veterinarian in appropriate choice of antibiotics.
Culture of the material in the ear canal is not necessarily required on the first visit, but I used to culture all recurrent infections because of concerns of antibiotic resistance. The absolute MOST drug resistant bacteria I've ever seen was cultured from a dogs ear. This was an old dog that basically had a 10 year history of completely random inappropriate treatment of "ear infections" ranging from inappropriate treatment by veterinarians to the owner randomly giving the dog her own antibiotics. I cultured a bacteria from that ear that was resistant to ALL first (ie penicillin), second (Ie cipro or Baytril), and almost all 3rd line antibiotics (ie methacillin, vancomycin). This thing was not just methacillin resistant (MRSA, which has been in the news lately) it was Vancomycin resistant also. I did the only thing I thought appropriate considering the resistance in that bacteria---I recommended euthanasia and cremation, which the owners did.
Dog ear canals basically have an L-shape to them. This L shape creates a pocket where bacteria can "hide" from liquid antibiotics put in the ear. This bend is out of sight from the outside (you have to move the ear to straighten the canal and see past it to the ear drum). All too often owners will not treat past the time what they can see from the outside goes away or worse yet, veterinarians will not followup with cytology after treating. What I recommended was start treatment, recheck in 2 weeks, continue treatmetn for 7-10 days after that if things looked like the infection was cleared up, but otherwise if there are yeast or bacteria present consider culture and or continue antibiotics for an additional 2 weeks and then repeat cytology.
Things didn't always work this way, but in essense there should be treatment for at least a week after clinical signs appear to have resolved.
Finally, BEWARE the "shotgun" type ear treatments on the market. I fail to see the medical logic behind a product that contains an antifungal, antibiotic, steroid, and who knows what else for treating a bacterial infection. Treatment must be appropriate for the infection that is present. This means antifungals need to be given for fungal infections. Oral antibiotics may be indicated for bacterial infections. Steroids DO NOT cure ear infections. But they may be indicated if there is a severe amount of inflammation and the dog is extremely uncomfortable. Beware though that products such as Otomax are capable of immunosuppressing some dogs to the point of causing symptoms of Cushings disease.
So basic rules of dog ear infections:
1) determine cause of infections--yeast or bacteria.
2) Treat appropriately with antifungals for yeast, antibiotics for bacteria
3) followup, followup, followup. This means repeat cytology, perform cultures, and reexamine the ears.
4) In the case of recurrent infections, the only way to prevent new infections is to identify the underlying causative agent (be it food alergies, hunting dogs swimming, owners who pluck ear hair and rinse the ears with water, to little kids spitting in the dogs ears). Once you identify that underlying cause, dealing with the ear infection becomes much easier.