Topical Antimicrobials for Otitis

Chapter 110


Topical Antimicrobials for Otitis



Canine ear disease is a prevalent and persistent problem and accounts for up to 15% of all canine veterinary case presentations. The large variety and quantity of veterinary topical otic preparations available demonstrate the demand for a wide range of therapeutics for this condition. Otic preparations that address bacterial, yeast, or mixed infections are usually combinations of corticosteroids and antimicrobials. Preparations designed for long-term control are mixtures of mild cleansers, drying agents, or disinfectants, and may contain antimicrobial agents.


Each case represents a different level of proliferation and exudate with a different degree of infection versus inflammation. Therapy needs to be targeted at each aspect of the condition. Becoming familiar with the products available and their effects is essential to formulating the best therapeutic plan for each patient. Since new products are continually introduced, some with familiar ingredients and some with newer antimicrobial agents, it is important to be aware of new products and new active ingredients that already may have been used by the client or by other veterinarians to treat the patient. Clients also may inquire about newer products that might be used to treat their pets.



General Properties of Topical Antimicrobial Formulations



The Vehicle


As with all forms of topical therapy, both multiple formulations and multiple vehicles are used in otic products. Each demonstrates specific properties that must be considered when selecting an appropriate product. The various vehicles use different mechanisms for delivery of active ingredients and also have different therapeutic, irritant, or cosmetic properties that determine their efficacy in practice. Formulations used for veterinary topical otic therapy include both solutions and suspensions. Different types of suspensions are lotions, creams, emulsions, and ointments. Solutions are homogenous mixtures in which the active ingredient is dissolved. In contrast, suspensions disperse fine particles within a less dense liquid.


Lotions tend to be liquids that evaporate leaving a thin layer of active ingredient (such as miconazole or another antimicrobial) in the ear. Lotions are likely to be drying because of their alcohol or propylene glycol content. Generally a “cooling” lotion or solution tends to contain alcohol, whereas a “soothing” one does not.


Creams, emulsions, and ointments are occlusive and prevent contact with the environment. These agents do not “dry” like lotions, but rather leave a moist layer with the active ingredient contained within. Creams create the least occlusive barrier and ointments are the most occlusive; emulsions share characteristics of each delivery system. In cases of exudative otitis, the use of an ointment may be contraindicated because increased water loss and drying are desired therapeutic outcomes.



Active Ingredients


Antibiotics, antifungals, and antiparasitics can be delivered using topical otic preparations. Additionally, various combinations of soothing agents, acidifiers, alkalinizing agents, keratolytic agents, keratoplastic agents, and astringents can be found in the range of available preparations. When a topical otic product is being selected, the patient’s specific infection, as well as the practitioner’s familiarity with the product, must be considered. Some practitioners and dermatologists prepare in-house otic remedies from injectable antibiotics or antifungal agents, or combine a variety of available otic products to create a single mixture to target a patient’s specific needs. This practice is a controversial and extralabel use of these drugs and is a topic beyond the scope of this chapter. However, if this approach is taken, it is important to remember that the stability and efficacy of the active ingredients may be affected. Additionally, the client must be clearly informed of the off-label formulation.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Topical Antimicrobials for Otitis

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