Study backs steroid-only option for canine otitis externa
Bottom line
A new randomized, double-blinded field study in Frontiers in Veterinary Science found that hydrocortisone aceponate monotherapy (Cortotic, Virbac) was non-inferior to the multi-agent otic gel Osurnia in 200 dogs with erythemato-ceruminous otitis externa in Japan. Dogs treated with Cortotic daily for 7 or 14 days had similar clinical improvement, cytology results, treatment success, and low relapse rates compared with dogs treated with Osurnia on days 0 and 7. By day 28, OTIS3 scores fell 72.1% with Cortotic and 76.1% with Osurnia, and both treatments were reported as well tolerated. (frontiersin.org)
Why it matters: For veterinarians, the study adds evidence that some cases of acute erythemato-ceruminous otitis externa may be managed effectively with an anti-inflammatory monotherapy rather than a routine antibiotic-antifungal-steroid combination. That matters in the context of antimicrobial stewardship, especially because FDA guidance for topical otitis products emphasizes showing when each component of a combination contributes meaningfully to effectiveness. The product labeling reviewed in the UK also notes that, in the clinical field trial, antimicrobial co-treatment was unnecessary and that bacterial and fungal overgrowth in these cases was often secondary. (frontiersin.org)
What to watch: Watch for whether this study changes first-line treatment habits, especially in dogs with inflammatory otitis where cytology suggests overgrowth may be secondary rather than the primary driver. (frontiersin.org)
Key facts
- Study type
- Randomized, double-blinded clinical field study
- Journal
- Frontiers in Veterinary Science
- Sample size
- 200 dogs
- Condition
- Erythemato-ceruminous otitis externa
- Country
- Japan
- Tested treatment
- Hydrocortisone aceponate monotherapy (Cortotic, Virbac)
- Comparator
- Osurnia multi-agent otic gel
- Main finding
- Cortotic was non-inferior to Osurnia
- Day 28 outcome
- OTIS3 scores fell 72.1% with Cortotic and 76.1% with Osurnia
A newly published clinical field study suggests veterinarians may not always need to reach first for a multi-agent ear medication in dogs with erythemato-ceruminous otitis externa. In the Frontiers in Veterinary Science trial, hydrocortisone aceponate monotherapy (Cortotic) was non-inferior to Osurnia, a combination product containing florfenicol, terbinafine, and betamethasone acetate, across clinical and cytological endpoints in 200 dogs. (frontiersin.org)
That finding lands in a therapeutic area where combination products have long been common, in part because canine otitis externa often presents with both inflammation and microbial overgrowth. But the study’s premise reflects a familiar clinical question: when yeast or bacterial proliferation is secondary to underlying allergic or inflammatory disease, does every case need topical antimicrobials up front? The authors frame erythemato-ceruminous otitis externa as an inflammatory condition that frequently involves secondary microbial infection, and the UK product documentation for Cortotic similarly states that bacterial and fungal otitis is often secondary in nature and that the underlying dermatologic condition should be identified and treated. (frontiersin.org)
In the trial, dogs with OTIS3 scores of at least 5 were randomized to either daily Cortotic for 7 or 14 days or Osurnia on days 0 and 7. Investigators assessed OTIS3 scores, cytology, and veterinarians’ subjective efficacy ratings. Results showed no significant difference between groups in OTIS3 reduction, cytological improvement, or treatment success at any time point. By day 28, OTIS3 scores had dropped 72.1% in the Cortotic group and 76.1% in the Osurnia group, while veterinarians rated efficacy as good or excellent in 83% and 87% of cases, respectively. Relapse was low in both groups, and both treatments were described as well tolerated. (frontiersin.org)
The broader product and regulatory context is important. Osurnia is labeled in the US for otitis externa associated with susceptible Staphylococcus pseudintermedius and Malassezia pachydermatis, and its labeling includes warnings tied to corticosteroid exposure as well as post-approval reports that include deafness, vestibular signs, tympanic rupture, and ocular injury from splatter after head shaking. Meanwhile, UK regulatory materials for Cortotic state that 201 dogs were included in the clinical field trial supporting the product and that a secondary reduction in bacterial and yeast overgrowth was demonstrated without concomitant antimicrobial treatment. (dailymed.nlm.nih.gov)
Industry and clinical commentary around otitis treatment has increasingly focused on stewardship and treatment matching. A 2025 Today’s Veterinary Practice review noted that many commercial otic products contain broad-spectrum antibiotics that should be reserved for cases with a bacterial component, and that for Malassezia-driven disease without bacterial involvement, an antibiotic-containing product may not be clinically necessary. That review did not discuss this new Frontiers paper directly, but it aligns with the study’s implication that more targeted prescribing may be appropriate in selected cases. (todaysveterinarypractice.com)
Why it matters: For veterinary professionals, this study may strengthen confidence in a more selective approach to topical otitis therapy, particularly when careful otoscopy, cytology, and case history point to inflammation-first disease. It also fits with FDA thinking: the agency’s guidance on topical infectious otitis externa drugs says combination products should demonstrate that each active ingredient contributes to effectiveness. In practical terms, the paper gives clinicians more evidence to support avoiding unnecessary antimicrobial exposure in appropriate cases, while still underscoring the need to identify primary causes such as allergy, manage pain and inflammation, and verify tympanic membrane integrity before treatment. (fda.gov)
There are still limits to how far the findings should be generalized. The study population was limited to dogs with acute erythemato-ceruminous otitis externa, not every presentation of infectious or chronic otitis, and the comparator was a specific combination product used on a fixed schedule. So this is best read as evidence for case selection, not as a blanket argument against antimicrobials in otic disease. (frontiersin.org)
What to watch: The next question is whether this evidence translates into guideline updates, wider uptake of steroid-only first-line treatment in selected cases, or additional head-to-head studies in chronic, recurrent, or clearly infectious otitis populations. (frontiersin.org)