What’s New in Otitis Externa Treatment Options

Otitis externa (OE) is one of the most common medical conditions affecting dogs worldwide.¹ There is no one-size-fits-all treatment approach, which is why a plethora of topical treatment options are commercially available. In choosing a treatment regimen, consideration should be given to infectious organism(s) present (if any), the condition of the ear canal (including the presence of exudate and/or biofilm), the client’s ability and willingness to medicate the patient, and management of the underlying cause(s).

Diagnosing OE should be based on patient history and otoscopic evaluation of the ear canals, tympanic membranes, and pinnae as well as cytologic evaluation of otic discharge. Cytologic evaluation is a critical part of the diagnosis and management of OE, and the presence and quantity of any rod-shaped bacteria, cocci-shaped bacteria, yeast, and/or white blood cells should be noted. Cytology results are essential for guiding initial therapy as well as providing a basis for monitoring response to therapy (which will influence treatment duration as well as treatment changes, if required).

Effective treatment of OE depends on an accurate diagnosis and treatment of infectious agents (if present); inflammation management; exudate removal; and management of any primary, predisposing, or perpetuating factors such as ectoparasites (e.g., Otodectes cynotis), allergic diseases (e.g., food allergy, atopic dermatitis), endocrine disorders (e.g., hypothyroidism), obstructive agents in the ear canal (e.g., foreign body, tumor), and/or excessive hair or moisture in the ear canal.² Secondary factors that may perpetuate or predispose a patient to otitis include bacterial or fungal infections, which must also be addressed with topical products (the most effective management option for OE).

Choosing a Topical Product

In choosing a treatment, there are multiple factors to consider: infectious agents found cytologically, degree of exudate in the ear canal, potential presence of biofilm, degree of inflammation in the ear canal, and client compliance ability along with patient temperament. Most commercially available otic preparations contain a combination of an antibiotic, an antifungal, and a corticosteroid (TABLE 1), enabling the practitioner to tailor therapy to the patient.

The most targeted therapy involves selecting the most appropriate antimicrobial component based on the type of infectious organism(s) found by cytology, thereby promoting excellent antimicrobial stewardship. As indicated in TABLE 1, most commercially available topical ear medications contain potent, broad-spectrum antibiotics such as aminoglycosides, which should be reserved for OE with a bacterial component. For patients with OE caused by Malassezia infection without a bacterial component, use of a topical product containing an antibiotic is not clinically needed. Treating the sole infectious agent (yeast) and inflammation will achieve clinical success while promoting excellent antimicrobial stewardship and preventing multidrug-resistant bacterial infections.

Applying topical ear medications may be complicated by fractious and painful patients, stenotic ear canals, and clients’ lack of understanding of proper application. Application difficulties can lead to treatment failure as well as increased owner stress and unfavorable behavioral changes in the patient. Long-acting ear medications that do not require client application are an appealing and effective treatment option because they do not rely on client compliance for success. Using a topical that is applied by a veterinary professional in the clinic ensures its accurate application while improving the client’s and patient’s quality of life.³

Managing Malassezia Infection with DuOtic

The first FDA-approved treatment for OE associated with susceptible strains of yeast (Malassezia pachydermatis) that does not contain an antibiotic is a terbinafine and betamethasone acetate gel (DuOtic; Dechra, dechra-us.com).⁴ DuOtic is available only by prescription and is to be administered by a veterinary professional. The 2-dose regimen dissolves in ear wax and treats infections for up to 45 days.⁵

Dosing and Administration

Each tube of DuOtic, which is equivalent to 1 treatment, contains 10 mg of terbinafine and 1 mg of betamethasone acetate in a gel formulation.⁵ Each dose of DuOtic is supplied in a premeasured, single-dose tube with a flexible, soft tip and should be applied into the affected ear canal(s). The treatment is not size- or weight-dependent, and 1 tube per ear is recommended for all patients.⁵ Treatments are administered in the clinic by a veterinary professional after cleaning and drying the ear canal.⁵ Administration should be repeated in 7 days.⁵ Treated ears should not be cleaned or additionally treated for 45 days.⁵

Mechanism of Action

Terbinafine is an allylamine, fungicidal antifungal.⁶ It inhibits squalene epoxidase, which catalyzes the synthesis of ergosterol from squalene. By limiting ergosterol, which is required for fungal cell membrane synthesis, and allowing for the toxic accumulation of squalene, terbinafine provides a dual mode of antifungal action.⁶ Betamethasone is a potent corticosteroid used to treat inflammation and associated pruritus. The otic product is in a gel formulation that dissolves in ear wax and is eliminated from the ear mechanically.⁵ Inactive ingredients in the otic product include propylene carbonate, glycerol formal, hypromellose, phospholipid, oleic acid, and butylated hydroxytoluene.⁵

Safety and Efficacy

Osurnia (Dechra, dechra-us.com) is another topical product indicated for treatment of OE associated with M pachydermatis yeast and susceptible strains of bacteria in dogs and contains the same concentrations of terbinafine (10 mg/mL) and betamethasone acetate (1 mg/mL) as DuOtic, plus florfenicol (10 mg/mL). Thus, the promising results of a study evaluating the efficacy of Osurnia⁷ also showed promise for DuOtic, which contains only terbinafine and betamethasone acetate. In that randomized, placebo-controlled field trial assessing the efficacy of Osurnia for the treatment of OE in 284 dogs with bacterial and/or fungal OE, Osurnia was found to be safe and effective.⁷ The most common infectious organisms isolated in that study were Staphylococcus pseudintermedius and Malassezia species. Osurnia was applied according to label instructions, which are identical to those for DuOtic, with 1 tube applied per affected ear canal(s) on day 0 and day 7. Treatment was superior to the placebo (vehicle); however, some improvement in both treatment and placebo groups was noted after the initial cleaning, supporting the benefit of thorough, in-clinic ear canal cleanings as part of OE management. Applications of Osurnia were well-tolerated with no reported significant adverse effects clinically or clinicopathologically. The veterinary-applied gel formulation offered a safe and effective treatment with excellent client compliance.

A sponsor-conducted, randomized, double-masked, placebo-controlled field study of DuOtic examined its efficacy in 197 client-owned dogs with yeast-related OE by using an overall severity score that summed the severity of the following clinical signs: erythema, edema/swelling, erosion/ulceration, and exudate.⁵ After the ears were cleaned with saline, either DuOtic or placebo was applied into the ear canal on days 0 and 7. Dogs were reassessed on day 45, and treatment was considered successful if the overall severity score for the affected ear was 3 or less, with no worsening of any clinical signs compared with day 0. The success rate was statistically significantly higher among dogs in the treatment group (62.21%) than in the placebo group (17.84%). The results of this study further support the effectiveness of terbinafine and betamethasone acetate gel for the safe and effective treatment of OE caused by yeast.

In terms of safety, DuOtic may cause ocular injury or irritation in animals or humans.⁵ People administering the medication are advised to wear protective eyewear, and the dog should be restrained after administration to prevent excessive head shaking and minimize ocular exposure.⁵ DuOtic should not be used in dogs with known tympanic membrane rupture and is not labeled for use in cats.⁵ No significant adverse effects have been reported.^2,3,5,7 The safe use of DuOtic has not been evaluated in dogs that are pregnant, lactating, or intended for breeding.

Indications

Use of long-acting DuOtic, which targets only Malassezia infection and inflammation, has multiple benefits in clinical practice.

First, it eliminates compliance concerns associated with clients and/or their fractious pets, ensures effective treatment application, and promotes both client and pet quality of life.

Second, the 2-dose regimen ensures follow-up care; the second application on day 7 allows for reevaluation and treatment adjustments if needed.

Third, the 45-day duration of treatment provides prolonged antifungal and anti-inflammatory management, which helps ensure complete resolution of the infection and reduces OE relapses.

Fourth, treatment for yeast without the addition of an antibiotic promotes excellent antimicrobial stewardship, which is increasingly relevant in veterinary medicine as antimicrobial resistance is viewed as an urgent health threat. Although many commercially available topical otic treatments target both yeast and inflammation, DuOtic represents the only long-acting, FDA-approved topical treatment that does not contain an antibiotic.

Summary

Canine OE is a common, often frustrating disease for which there is a plethora of available treatments. Diagnosis should include cytologic findings to enable a more tailored treatment approach and accurate assessment of response to therapy at follow-up evaluations. In choosing a treatment, there is no one-size-fits-all approach; most commercially available products are a combination of an antibiotic, antifungal, and anti-inflammatory agent. Choosing a targeted treatment, such as DuOtic, the first antibiotic-free, FDA-approved treatment for yeast OE in dogs, is a safe and effective option that enables clinicians to promote excellent antimicrobial stewardship while also increasing client compliance.