Canine otitis externa, Pseudomonas

A Golden Retriever with Otitis Externa and Pseudomonas

This is a specific case of canine otitis externa shared by a fellow member of VetHive where I am a dermatology guide. This case is a COMMON one and I wanted to share it case so we can review some of the important specifics! 

Also, after this veterinarian read my response she said "everyone should join VetHive"! She is #notwrong. Mention my name "PAINTER" in your coupon code and receive 10% off! 

Here we go! Let's do this case! 

Hi there! This is a case of a colleague of mine at my clinic. Willow is an 11yo FS Golden Retriever with chronic allergies that manifests as pyoderma and recurrent ear infections. She is currently on Apoquel SID and bought a bag of Hill’s Derm Complete yesterday. On Nov 15/23 she had 4+ rods AU on ear cytology and was treated with Otomax with no resolution. An ear culture was done at the recheck Nov 30/23 - it came back sensitive to Polymyxin B so Surolan was given, however no resolution. Yesterday her cytology showed 4+ rods, 1+ cocci, 1+ WBCs. She was put on oral marbofloxacin and given a shot of dexamethasone at 0.1mg/kg IM, and she is hoping for some help regarding the best topical to try next. Please see her culture results attached - Is enterococcus faecalis one we need to worry about? She was thinking of starting Ciprodex but was worried since the E. faecalis is resistant to it. She’s hesitant about GA in her pet and I’m not sure if she would be up for referral for a deep ear flush/myringotomy. Thanks so much in advance!

(case presented with permission from submitting doctor, BTW!). 

There is SO much to pick apart in this question! I am excited to share with you all some of my thoughts! 

It is important to remember before we get started that there is never a "right" answer when it comes to these complicated otitis cases. I share this for your learning, but never want to you to feel like there is a "right" or "wrong" way to do things. Some dermatologists might approach this case differently; that's okay. I might change my approach in a few years as information is updated or new medicine options become available; that's okay. We're all here to learn, grow, share, and help our patients

Here's the culture: 

And, here is my response! 

Great question, and complicated case!

When it comes to otitis externa in dogs, we have a great system called PSPP which can help us organize our differentials and plan in a way that is comprehensive and practical. Have you heard of PSPP? If not, I encourage you to check out this podcast episode of Your Vet Wants You to Know that reviews the system! This is an episode meant for pet owners, but it is useful for veterinarians just the same! 

PSPP is the system that I use to formulate my diagnosis and plan for managing all otitis cases. This is a really great review from a trusted colleague and dermatology "grandfather" (we all love you, Dr. Halliwell). If you would like to read more, check that article out! 

But, in summary: 
Primary - the factors that induce otitis in a normal ear 
Secondary - the infection type 
Perpetuating - chronic changes that are difficult to resolve 
Predisposing - genetics, factors that make otitis more likely

But, let's get specific to this case here! How does PSPP apply to this case with a culture of Pseudomonas? How could PSPP possibly help this veterinarian organize her plan for this dog? 

START at the TOP!

PRIMARY 1a: This is an allergic Golden. The reason that this dog is developing otitis externa is because she has allergies. I would like to do a study on why Goldens seem more prone to Pseudomonas otitis because these dogs get the short end of this stick for sure.

You owe it to this dog to formerly work up the underlying cause of the otitis. If you never do this, she will always have inflammation which drives secondary infection.

Working up the underlying cause of otitis involves asking the question: what percentage of this dog's problem is driven by food?

The reason that we work up food first is because there is no diagnostic test for allergic disease that will answer this specific question for you. You have to either have demonstrable seasonality OR perform a diagnostic diet trial to get your  diagnosis. Want to learn more about this? Check out my *new* online course dedicated to allergen testing, diagnosing canine atopic dermatitis, and immunotherapy @ 

PRIMARY 1b - let's talk a little more about food allergy. While their company-published evidence is quite good, I am not at all ready to trust Derm Complete. 

My favorite lecture to give is on diet trials, why I select what I select, how to coach people, etc. And, I am hoping to make a short course on this for the start of 2024 (

Also, Dr. Lancellotti and I have a great deep dive and resource for pet owners in her podcast Your Vet Wants You to Know - Episode 017.

Lots of resources for you to make sure that you are getting this primary cause diagnosis correct! 

For this dog, I would go ALL IN with the diet trial. This owner needs to start a hydrolyzed diet strictly for 8 weeks - my preference is Royal Canin HP. We can review why this is my preference in my blogs to come! Don't you worry! 

A diagnostic diet trial should *definitely* be done if this dog has any history of soft stool or GI signs. This veterinarian should ask this owner what the stool of her dog looks like. I use this chart and have owners point to their dog's poop (versus ask if their dog's poop is normal; you would be amazed what some people think is normal!). 

Ears and rears are a red flag for food allergy. And, honestly, this is the best primary cause of otitis to have. Why?! Because we can really make a difference for these dogs! If we reduce the inflammation caused by their diet, then we can reduce the inflammation that is causing their ear infections. Some dogs can make a complete recovery if this is their sole primary trigger! 

I have more to say on this (haha, like could talk for days about food allergies in dogs), but this is where I will leave it. Trust there will be more posts to come on this! What is to take away is the fact that: 
1) There is a primary cause of these infections 
2) A diagnostic diet trial is the only test that is currently available to determine what percentage of your patient's problem is driven by food 
3) Determining the root cause of your patient's otitis externa can make a major difference in their overall well-being and need for medical management 

PRIMARY 1c - All primary causes are inflammatory. Allergic disease is an inflammatory condition of the skin and ears. This veterinarian mentioned that this dog has been on Apoquel, but has struggled with secondary infection of the skin and ears despite. This is a *key* way to determine that your medical management plan is not working and exactly what I discuss in my course Medication Masters

But, let's talk about what we can do for this dog today.

This dog needs prednisone. Period. That injectable dex is not something I would have even really considered an option. We use that more in an ER setting for conditions like respiratory distress, asthma, urticaria, acute reactions, etc. 

For chronic diseases of allergy like canine atopic dermatitis with secondary otitis, we need to consider a nice, long 4-6 week taper of prednisone starting at 0.5-1.0 mg/kg PO SID.

Make sure to get bloodwork before starting steroids. And, make sure your patient is not on NSAID medications! Sometimes owners forget to tell you that they randomly give NSAIDs after hikes, etc. So, I always make sure I explain the importance of steroid safety. I also review steroid side effects. 

Short-term side effects of steroids --- increased thirst and appetite, frequent urination, panting, occasional lethargy, occasional vomiting/nausea, occasional diarrhea 

Oh, and, my course has a boat load of handouts for pet owners on this subject! So....yeah, if you haven't signed up, you should today

And, Apoquel isn't doing anything for this dog; I would discontinue and consider starting cyclosporine as the next step. But, we can review that in another blog! Stay tuned! This is an important concept to get down and I think veterinarians are confused about what medication to pick for their patients and why. Totally get it. I am here for you! Standby for more! 

But, the important lesson here is this: 

When you are facing a refractory otitis externa case, I would bet that your weak link is inflammation. You likely haven't done one or more of the following: 
1) Addressed the root cause 
2) Added in prednisone to reduce inflammation 

Doing each of these things is often key for all dogs with otitis externa. 

[we aren't talking about neoplasia of the ear in this article, but I just want to mention that this is an important primary cause to rule out in dogs with unilateral or refractory disease; just felt like now was the time to remind you of this! We can talk about how to do this in future blogs!]. 

That wraps up what I want to say about primary disease for this specific case! That was a lot, right? YES! But, it is so important because it is the key problem and root of all otitis cases! If you aren't asking "what is this dog's primary cause of their ear infection?", then you are missing a large part of the dog's problem! 

PSPP.......let's go to S! 

SECONDARY - This veterinarian performed cytology and saw bacteria! Great. And, you have a culture that is showing two bacteria, both of which demonstrated marked multi-drug resistance. Ouch!

A word on cultures. I tend to reserve the ear culture for when I am performing myringotomy and treating otitis media using systemic antimicrobials. I also will consider a culture when I have a refractory otitis for which I am already addressing primary, perpetuating, and secondary factors.  

Cultures shouldn't be a replacement for cytology. And, we should not be using them to determine what topical to use. The reason is that the culture gives MIC information for systemic antibiotics, not necessarily topical ones. Though some cultures will provide this information, that is really not the ideal point of them. 

In this case, it certainly wasn't wrong to have a culture. This case has been chronic and terrible; the ear is a dumpster fire. BUT, if you're picking up the culture swab - you should also make sure you are picking up all the primary cause options! 

Check out this study -

This is showing us that cytology agreed with culture results only 68% of the time. So, it is important to do both, and to recognize that there isn't a single perfect test for the ear when it comes to infection determination and treatment. 

*** The biggest mistake that I see veterinarians making about ear cultures is their tunnel vision around them. They see the culture, the bacteria, the results and they focus just on that. This is why PSPP helps you navigate this wickedly complex problem that just can't be boiled down into a single culture *** 

So, let's talk about Pseudomonas.

This is a GREAT review -,from%20the%20ear%20canal%2C%20aural

This bacteria is a hardcore opportunistic pathogen. 

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacillus found in soil, water, and decaying organic matter. It is not a normal inhabitant of the canine ear and when it leads to infection, it can be challenging to manage.

In this particular case, you can see that there are few options for treating this infection. Both Marbofloxacin and Enrofloxacin are listed as intermediate sensitivity against Pseudomonas. Ciprofloxacin is marked as sensitive. 

In this case, I would go with Enrofloxacin at the upper end of the dose range. And, I would make sure you are treating for 2-3 weeks past clinical clearance. Given the chronicity for this dog, this will likely be at least 6-8 weeks. And, if this veterinarian did not address the primary cause of this dog's inflammation - that could be forever. 

What's up with ciprofloxacin? Variable absorption in dogs, and not something I generally reach for. Here's why -

For a TOPICAL - I would go Surolan. This has Polymixin B and you can try this in concert with the marbofloxacin. But, this dog has been on Surolan without much improvement. I would still use it since it is commercially available AND you will add in some primary cause treatments! So, let's get the Surolan on board, prednisone in the mix, and a diet trial. Could be a whole new scenario! 

Could we do a compounded Amikacin or Ceftazidime product? Yes! That would be my next step. But, I try to limit use of these important antimicrobials. 

Now...what's next? Here's a beautiful graphic from this awesome review article from a colleague Dr. Koch! 

PERPETUATING - Perpetuating changes are chronic acquired pathological changes in the ear canals that prevent resolution. Early changes include nodular epidermal and glandular hyperplasia giving the ear canals a “cobblestone” appearance. Later changes include further epidermal and dermal hyperplasia and thickening, ear canal stenosis and occlusion, fibrosis, and mineralization. This can also result in tympanic membrane rupture, otitis media, and cholesteatoma formation.

This is the top reason why Pseudomonas ears are hard to resolve! This bacteria brings about so many pathologic problems, ears don't stand a chance! We will see lots of biofilm, chronic inflammatory changes, and other problems within the canal that prevent complete resolution. The VO procedure helps to identify and manage these. And, cleaning at home is important to reduce the formation of biofilm, assist with the appropriate pH of the canal, and remove discharge that prevents topical medication penetration. 

I want to have a separate article on cleaning and the VO procedure. Gotta keep this article somewhat brief. But trust that these cases will often require some cleaning under general anesthesia to help reset that ear canal environment. 

PREDISPOSING - this is a Golden. They get Pseudomonas like it is their job. Poor things. Not all Goldens will develop otitis, but the ones with allergy are more likely to because they have a predisposing genetic factor. 

Viola! PSPP! 

Ears. Complicated little organs. Let me review some key points: 
1) Prednisone - long, slow taper that is at an anti-inflammatory dose
2) Surolan until clinical resolution (weeks)
3) Marbofloxacin until clinical resolution (weeks)
4) Diagnostic diet trial, 8 weeks, strictly fed, Royal Canin HP
5) Make sure you have your root cause in mind 
6) Consider perpetuating factors for refractory cases 
7) Talk with pet owners about the importance of long-term treatment and buy-in; our podcast really helps! 

What questions come up with this case? Does this help you as a resource? Happy learning and helping these patients with allergy manifestations! 

Here's a list of some references and resources: