Interesting article on this:

Example of help for an ME dog owner: (NOT to be used without discussion with your veterinarian)
Hi _____ – the 4-6 week advise for antibiotics comes from 3 “sources:”

  1. Specialists recommendation on VIN (Veterinary Information Network)
  2. Our experience here: i.e. too many owners report rapid recurrence of AP after 10-21 days of antibiotic treatment, so, after some research, we started advising the 4-6 weeks. These dogs have more respiratory “disadvantages,” if you will, than dogs with healthy esophagi. They are prone to reflux and what I call “micro-aspiration,” for lack of a possibly more appropriate term. So, we need to have these dogs on a protracted antibiotic regimen. And, in those dogs who have been “appropriately” treated, who develop AP soon after discontinuing antibiotics, we advise the consideration of daily albuterol nebulizer treatments. There have been owners report that their dog, who had been on almost constant antibiotics for months or years, was able to be removed from constant antibiotics because of the nebulizer treatments, possibly because the albuterol dilates the deeper bronchioles, allowing “stuff” to be coughed up more easily, minimizing re-excacerbation of AP.
  3. In human medicine, with severe pneumonia, people can be on antibiotics for months.