Comparison of single or two dose veterinarian-administered protocols and daily at-home prescription canine otitis externa treatments

You are presented with an 18-month old male entire Labrador retriever with bilateral aural pruritus and pinnal erythema. Following physical and otoscopic examination, you diagnose the dog with otitis externa. Cytology of aural discharge demonstrates a moderate overgrowth of cocci and Malassezia. The tympanic membranes are both visible and intact and you elect to prescribe treatment with a topical polypharmacy otic suspension. In your practice, you have a choice between a once-daily at-home treatment and long-acting products that are applied in the clinic. The owner asks if the long-acting product might be more effective. You decide to consult the evidence to determine the best course of action.

The evidence

Three studies were identified (Heur et al., 2024, King et al., 2018, and Noli et al., 2017), all of which were randomised control trials. King et al. (2018) and Heur et al. (2024) were single blinded, while Noli et al. (2017) was not blinded.

Heur et al. (2024) studied 276 client-owned dogs diagnosed with acute or recurrent otitis externa in one or both ears at veterinary clinics in France, Germany, and the Netherlands. Group A (143 dogs) were treated with a single application of otic suspension by veterinary staff and their ears were cleaned with saline prior to application. Group B (133 dogs) were treated with two applications of 1 ml of otic gel on days 0 and 7 by veterinary staff. Ears were not cleaned prior to treatment. The outcome studied was a clinical ear score otitis index score (OTIS-3) which was determined on days 0, 7, 14, 28, and 42.

King et al. (2018) studied 285 client-owned dogs diagnosed with acute or recurrent otitis externa in one or both ears from first opinion practices in France, Germany, and the UK. Group A (148 dogs) had their ears treated with two doses of polypharmacy otic gel on day 0 and returned to the practice for retreatment on day 7. Clinical checks were completed on days 28 and 56. Group B (137 dogs) was treated with an initial dose of a polypharmacy otic suspension at the clinic, and further doses at home by their owners, who were sent home with instructions to administer it once daily for four days. Dogs were re-evaluated by a clinician at 7, 28, and 56 days. The outcomes studied were; OTIS-3 scores, assessment of the patient’s response to treatment by owners and clinicians at days 28 and 56, and the frequency of dogs with either a bacteriological or fungal response at day 28 or 56.

Noli et al. (2017) studied 50 client-owned dogs diagnosed with acute or recurrent otitis externa in one or both ears in multiple veterinary practices in Italy. Group A (25 dogs) were treated with two applications of a polypharmacy otic gel on days 0 and 7 by a clinician. Group B (25 dogs) was given a once-daily application of a polypharmacy otic suspension applied by an owner for 14 days. The outcomes studied were; OTI-3 scoring, quality of life of owner and dog measured via a questionnaire, and pruritus using a Visual Analog Scale (VAS) on days 0, 7, 14, and 28.

Limitations of the evidence

The overall strength of the evidence is strong, owing to robust study design. However, there were some limitations to the evidence.

Heur et al. (2024) only studied objective outcomes. Studying subjective outcomes as well would have added weight to the findings. Additionally, ear swab samples were taken on days 0 and 28 for microbial culture and antibiotic and antifungal susceptibility testing, but the results were not elaborated on. Cytology of aural discharge would have been a useful addition. Finally, the impacts of ear cleaning being completed in one group but not the other were not evaluated.

King et al. (2018) was a single-blinded study, but the study design did not allow for the blinding of owners which could potentially lead to bias in the reporting of treatment. Additionally, different treatment responses were caused by antimicrobial resistant Pseudomonas aeruginosa which falls outside the scope of the research question above. Finally, the study’s authors were employees of a pharmaceutical company which may have caused bias.

Noli et al. (2017) was the only study of the three evaluated to not be blinded, which increases the potential for bias. All patients that participated were sent home for the duration of the study which may have exposed them to external factors that may have skewed the results, but is also reflective of real life cases. Finally, there were some statistical limitations; effect size was not calculated or reported, and confidence intervals were not reported.

Summary of findings

King et al. (2018) and Noli et al. (2017) present strong evidence that single or two-dose treatments applied by a clinician are as effective as daily treatment administered at home at treating canine otitis externa. However, not all of the studies directly compared long-acting treatments with at-home daily treatments. Heur et al. (2024) only compared the efficacy of using one or two long-acting treatments, so its findings are less applicable to this subject.

Heur et al. (2024) found that both treatment groups had a high success rate. Group A was treated with a single application of a polypharmacy otic suspension on day 0 with patients’ ears cleaned with saline first, and 89.5% (128/143 dogs) experienced treatment success. Group B was treated with two applications of a polypharmacy otic gel on days 0 and 7, and 87.2% (116/133 dogs) experienced treatment success. The p-value was found to be less than 0.0001, meaning these results are statistically significant.

King et al. (2018) found that both the clinician administered polypharmacy otic gel and owner administered polypharmacy otic suspension reduced clinical signs as recorded via the OTIS-3 scoring system. By day 28 and 56 respectively the OTIS-3 decreased on average by 62.5% and 63.6% for the clinician applied otic gel group, and 63.4% and 60.5% for the owner applied polypharmacy otic suspension group. Three quarters of clinicians and owners reported a good to excellent response to the clinician applied polypharmacy otic gel administration after day 28, which was not significantly different to the owner applied polypharmacy otic suspension. On day 56 there were no differences between the two groups in overall assessment scores carried out by investigators and owners.

Noli et al. (2017) found no difference in the OTI-3 percentage improvements between Group A (polypharmacy otic gel applied by a clinician) and Group B (polypharmacy otic suspension applied by owners). Both treatments were equally effective at improving pruritus by days 14 and 28, but the polypharmacy otic gel had a more rapid onset of action, with higher improvement by day 7.

Conclusion

Veterinarian-administered polypharmacy otic gel treatments show comparable efficacy in reducing the clinical signs of otitis externa in adult dogs when compared with owner-administered polypharmacy otic suspension. Both treatments demonstrated similar success rates with no significant differences, all of which is bolstered by the overall strength of the evidence.

Deciding on the best course of action can therefore come down to contextual factors. The contextualised care resources on the RCVS Knowledge website may be helpful in this regard.

Additionally, as many of the longer acting products referenced in this article contain broader spectrum antimicrobials than their at-home alternatives, there may be antimicrobial stewardship considerations to take into account. The RCVS Knowledge website has resources that may help in this regard.

Disclaimer

The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise; patient’s circumstances and owner’s values; country, location or clinic where you work; the individual case in front of you; and the availability of therapies and resources.