Why Your Dog’s Ear Infection Keeps Coming Back
Addressing the underlying cause is the key to breaking the cycle
You’ve treated the ear infection. The cytology looked clear. The dog stopped shaking its head. Then, three months later, they’re back with the same problem.
Sound familiar?
In most cases, the infection isn’t the real problem. It’s a symptom.
The 91% Solution Most Practices Miss
When topical medications fail to resolve otitis externa, many practitioners reach for oral antibiotics. But one study found a simpler answer: 91% of dogs with treatment-resistant otitis resolved completely after a deep ear flush under sedation.¹
The culprit? Debris, ceruminoliths, and biofilm sitting at the level of the tympanic membrane that topical medications can’t reach. Until you physically remove that material, the infection persists.
If a case is not responding to a single course of treatment, especially with yeast, the next question should be: does this ear need to be flushed under sedation?
Biofilm: The Hidden Reservoir
Biofilm isn’t just a buzzword. It’s a protective matrix that shields bacteria and yeast from antimicrobials.
The organisms most likely to produce biofilm? The same ones causing most ear infections: Staphylococcus, Pseudomonas, and Malassezia. A 2023 review found biofilm formation in 40 to 95% of Pseudomonas aeruginosa isolates from cases of otitis externa.²
Standard topical antibiotics need bacteria to be actively replicating to work effectively. Bacteria hiding in biofilm aren’t replicating. They’re waiting.
Breaking down biofilm requires specific agents: Tris-EDTA, N-acetylcysteine (NAC), silver-based products, or aggressive flushing. Tris-NAC solution is a practical choice for cases where that mucoid, slimy discharge suggests biofilm involvement.
The Long-Acting Advantage
Compliance is a persistent problem in otitis management. One social media analysis found veterinarians are 20 times more likely to discuss compliance issues with ear medications than with other treatments.¹
The problem with traditional ear drops? Owners can’t count drops, they don’t know how much is “a good squeeze,” and self-reported non-compliance with drop-based regimens is high.
Newer long-acting formulations change the equation:
- Single application products (Claro, Simparica): Clean, instill, done for 30 days
- Two-application products (Osurnia): Day 1 and Day 7, then 45 days efficacy
- Weekly installations (Easotic): Once weekly for maintenance
For an aggressive dog where only one intervention is possible per visit, long-acting products let the clinician treat and be done.
The Allergy Connection
In a study of 60 dogs with Pseudomonas otitis, 70% had allergies as the primary underlying cause.³
The breakdown:
- 42 cases: Allergies
- 8 cases: Masses
- 7 cases: Endocrine disease
- 3 cases: Autoimmune
If your patient has had more than one ear infection, the question isn’t “what antibiotic should I use?” It’s “what’s causing the inflammation that allows infection to take hold?”
Why Cytopoint and Apoquel Don’t Always Help the Ears
A common clinical observation: Cytopoint or Apoquel controls the allergic dermatitis on the rest of the body, but the ears persist as a problem.
The ears require more anti-inflammatory intervention than these targeted itch medications provide. For patients on Apoquel or Cytopoint with persistent otitis, consider:
- Adding topical steroids to the ear regimen
- Switching to cyclosporine (more anti-inflammatory for chronic otitis)
- Allergen-specific immunotherapy for long-term control
Practical Takeaways
- Cytology first, always. You can’t treat what you haven’t identified.
- Consider a deep ear flush for cases not responding to topicals.
- Think about biofilm when you see mucoid discharge.
- Use long-acting formulations to improve compliance.
- Address the underlying cause. Recurrent otitis usually means uncontrolled allergies.
- Volume matters. A Great Dane needs more medication than a Yorkie.
The goal isn’t just clearing this infection. It’s preventing the next one.
This post is based on a VetOnIt CE webinar by Dr. Jason Pieper, DACVD. For RACE-approved dermatology CE, visit our on-demand library.
References
¹ Pieper J. Management of Otitis Externa. VetOnIt CE Webinar, 2025.
² Secker B, et al. Pseudomonas spp. in Canine Otitis Externa. Microorganisms. 2023 Oct 28;11(11):2650. doi: 10.3390/microorganisms11112650. PMID: 38004662.
³ Paterson S, Matyskiewicz W. A study to evaluate the primary causes associated with Pseudomonas otitis in 60 dogs. J Small Anim Pract. 2018 Apr;59(4):238-242. doi: 10.1111/jsap.12813. PMID: 29322531.