A retrospective multicentre study of client-owned dogs with allergic otitis externa has reported that 70.4 percent of 71 dogs had no relapse during a fixed 12-month observation period while receiving proactive maintenance therapy with hydrocortisone aceponate ear spray, and a further 16.9 percent had only a single flare. The study, reported in line with STROBE guidance for observational research, followed dogs that had entered maintenance treatment only after clinical and cytological remission of their active ear disease had been achieved. Because the study had no untreated control group, it cannot prove that the spray caused the low relapse frequency; it shows only that relapse was uncommon in dogs that continued the intended regimen under stable allergy management.
In allergic dogs, inflammation of the external ear canal may occur as a primary manifestation of disease, may accompany more generalised skin signs, or may persist after apparent control of itching elsewhere. Once inflammation is established, changes in the ear canal microenvironment favour cerumen accumulation and secondary yeast or bacterial overgrowth, and repeated episodes may promote chronic structural changes that further complicate long-term control. For this reason, management of allergic otitis externa is not limited to treating active infection; control of the underlying inflammatory component is considered central to reducing recurrence, limiting repeated antimicrobial use and preventing progression towards chronic ear canal changes.
Hydrocortisone aceponate is a non-halogenated diester glucocorticoid developed for topical use, with a pharmacological profile intended to provide local anti-inflammatory activity and limited systemic exposure. Previous studies in canine atopic dermatitis reported clinical efficacy without detectable adrenal suppression during short-term use, and a more recent evaluation in dogs with erythemato-ceruminous otitis externa found that short-course treatment improved clinical signs similarly to an antimicrobial-containing combination product. Retrospective data have also supported its use as part of reactive and proactive management of chronic or recurrent non-infectious otitis externa, with 79.1 percent of treated ears remaining recurrence-free over a mean follow-up of 202.6 days in that earlier study, which analysed ears rather than dogs and used variable follow-up.
What remained unknown was how dogs fared over a full year of maintenance, and whether the exact weekly schedule mattered. Prescribing habits vary: some clinicians instruct owners to apply the spray on two consecutive days each week, while others favour two non-consecutive days separated by at least two treatment-free days. The new study therefore set out to describe relapse frequency over a fixed 12-month period and, secondarily, to compare the two schedules without assuming equivalence. The unit of analysis was the dog; when both ears were affected, classification followed the more severe or clinically relevant otitis phenotype recorded before maintenance therapy began.
Case selection was strict. Records were screened for dogs diagnosed with allergic otitis externa on the basis of compatible history, clinical, cytological and otoscopic findings, with exclusion or treatment of secondary infection and of other primary causes such as ectoparasites and foreign bodies. Food allergy was assessed where clinically indicated using elimination diets and oral food challenges, and atopic dermatitis was diagnosed using accepted clinical criteria after exclusion of relevant differentials. Maintenance therapy could begin only after remission of the active episode, and concomitant allergy management, including systemic antipruritic or anti-inflammatory treatment, allergen-specific immunotherapy and diet, had to remain unchanged throughout the observation year. Of 104 dogs initially prescribed the spray, 71 met the final criteria; 33 were excluded because treatment was not started or continued, schedules or allergy management changed, owner telephone follow-up could not confirm the required information, or complete 12-month data were unavailable.
The cohort reflected the breeds and presentations familiar in small-animal practice. Forty-six breeds were represented, with French Bulldogs and English or American Cocker Spaniels most frequent at eight dogs each, followed by Labrador Retrievers with six. Otitis was bilateral in 55 of 71 dogs before maintenance therapy and unilateral in 16. Ceruminous otitis was the most common clinical type, seen in 54.9 percent of dogs, followed by erythematous, purulent and ulcerative forms. Baseline cytology most often identified Malassezia species, while no organisms were recorded in 23.9 percent of cases. Thirty-six dogs received the consecutive-day protocol and 35 the non-consecutive-day protocol, with allocation reflecting the attending clinician’s judgement rather than randomisation. One baseline difference emerged: dogs on the non-consecutive schedule were older, with a median age of 7 years versus 5 years, a difference the authors could not rule out as a confounding factor.
Over the 12 months, 50 of 71 dogs had no relapse, while 21 dogs, or 29.6 percent, had at least one episode requiring veterinary examination, cytological confirmation and additional otic treatment. Twelve dogs had a single relapse and nine had multiple relapses, defined as two or more. The total count of 39 relapses across 71 dog-years corresponds to 0.55 relapses per dog-year for the whole cohort. Because every dog contributed exactly one year of observation, relapse count per dog is equivalent to the relapse rate, allowing straightforward comparison between schedules. During maintenance, clinically stable dogs also received a chlorhexidine-based ear cleaner once weekly, applied 24 hours before the spray, regardless of protocol. Rescue treatment for relapses was selected according to otoscopic and cytological findings, with specific topical combination regimens for Malassezia overgrowth, coccal, rod-shaped, mixed and Pseudomonas infections.
The schedule comparison produced numerical differences that did not reach statistical significance. At least one relapse occurred in 25.0 percent of dogs on consecutive-day treatment and 34.3 percent on non-consecutive treatment, with a relative risk of 1.37 and a 95 percent confidence interval of 0.66 to 2.84. Multiple relapses showed a wider numerical gap, 5.6 percent versus 20.0 percent, yielding a relative risk of 3.60 with a confidence interval of 0.80 to 16.15 and a p value of 0.085. Total relapse counts were 14 versus 25, corresponding to rates of 0.39 and 0.71 relapses per dog-year, but median relapse count was zero in both groups and counts did not differ significantly. The authors are explicit that the study was neither designed nor powered as a non-inferiority or equivalence trial, and they frame the apparent advantage of consecutive-day dosing as hypothesis-generating rather than confirmatory.
The limitations deserve as much attention as the results. Treatment allocation was not randomised, so unmeasured differences in previous relapse patterns, ear canal changes, owner adherence or clinician preference may have shaped which schedule each dog received, and the age difference between groups cannot be excluded as a confounder. By retaining only dogs with confirmed treatment continuation, stable concomitant allergy management and complete records, the analysis offers a cleaner estimate of relapse among adherent patients, but it also introduces selection bias: dogs that stopped treatment, used the product incorrectly or could not be contacted are not represented. Relapse was defined more strictly than owner-reported recurrence, yet retrospective assessment remains vulnerable to recall and recording bias, minor owner-managed episodes may have been missed, and inconsistently recorded relapse dates prevented any time-to-first-relapse analysis. Adherence was confirmed by owner report rather than objective measurement.
Even with those caveats, the findings align with a broader proactive-treatment concept. Prospective placebo-controlled work in canine atopic dermatitis showed that intermittent hydrocortisone aceponate spray prolonged time to relapse of cutaneous lesions, and previous trials documented reductions in skin lesions and pruritus without adrenal suppression. The new data extend that framework to the ear canal, using the dog as the unit of analysis and a fixed 12-month window that allowed relapse frequency and rate to be quantified directly. The authors position their results as support for further prospective evaluation of proactive topical anti-inflammatory maintenance therapy in allergic otitis externa, including adequately powered comparisons of maintenance schedules and standardised assessment of relapse timing. For now, the message is measured: in a verified adherent cohort, most dogs had no relapse or only one relapse over a year, and whether two consecutive days differ from two scattered ones remains an open question for a larger controlled trial.
Subject of Research: Proactive topical hydrocortisone aceponate maintenance therapy for allergic otitis externa in dogs
Article Title: Proactive Treatment of Canine Allergic Otitis Externa With Hydrocortisone Aceponate: A Retrospective Observational Study
Article References: Maina, E., Rigert, J. C., Filippini, C., Cao, R., & Oliveira, A. (2026). Proactive Treatment of Canine Allergic Otitis Externa With Hydrocortisone Aceponate: A Retrospective Observational Study. Veterinary Medicine and Science, 12(6), Article e71276. https://doi.org/10.1002/vms3.71276
Image Credits: AI Generated
DOI: 10.1002/vms3.71276
Keywords: canine otitis externa, hydrocortisone aceponate, allergic skin disease, atopic dermatitis, veterinary dermatology, topical glucocorticoid, maintenance therapy, relapse, retrospective study, ear canal inflammation, Malassezia, dog health
