Pharmacology of Otic Products - Veterinary Medicine

Otic Products Pharmacology

• Course: Pharmacology and Therapeutics II, Integrated Master in Veterinary Medicine 2024-25
• Lecturer: Ana Oliveira, MV, MSc, Dip ECVD, PhD, EBVS European Specialist in Veterinary Dermatology
• Topic: Pharmacology of Otic Products

Ear Anatomy

• The ear has three parts: outer, middle, and inner.
• Outer ear: Includes the pinna and ear canal.
• Ear canal: Carries sound to the tympanic membrane (eardrum).
• Ear canal shape: "L" shaped, where cerumen and secretions accumulate.
• Middle ear: Includes the tympanic membrane, auditory ossicles (transmit & amplify vibrations), and eustachian tube.
• Inner ear: Includes the cochlea (hearing) and vestibular apparatus (balance).

Otitis Externa

• Symptoms of External Ear Canal Problems: Pruritus (itching), pain, inflammation, shaking of the head, excess cerumen, and change in smell.

Ear Canal Cleaners

• Types: Ear canal cleaners
• Medication to treat otitis: Include treatments for infections

Characteristics of Ear Canal Cleaners

• Ceruminolytics/Surfactants: Used to clean the ear canal, emulsify debris, break it up, keep it in solution.
• Astringents: Dry the ear canal surface, preventing maceration.
• Low pH & Antimicrobials: Maintaining a low pH along with antimicrobial agents inhibit microbial proliferation.
• Ototoxicity: Some ear cleaners (not water, saline, or squalene) can be ototoxic (harmful to the ear).

Ceruminolytics

• Composition: Organic oils and solvents (propylene glycol, lanolin, glycerin, squalane, etc.).
• Use: Effective in mildly waxy or dirty ears, relatively safe for routine at-home cleaning when the tympanic membrane is intact.

Surfactants

• Action: Efficient with both ceruminous and purulent debris. Emulsify debris, keeping it in solution.
• Precautions: Some detergents can annoy the middle ear mucosa and are not appropriate if the ear drum is ruptured.
• Examples: Dioctyl sodium sulfosuccinate (DSS or docusate), calcium sulfosuccinate, and other detergents.

Foaming Agents

• Action: Release oxygen in situ, dispelling debris and aerating canals.
• Potential concern: Causes anxiety in some animals.
• Availability: Not available in all countries.

Astringents

• Action: Dry the ear canal surface, prevent maceration.
• Combination: Often used together with keruminolytics and surfactants.
• Examples: Isopropyl alcohol, boric acid, benzoic acid, salicylic acid, sulfur, aluminium acetate, and silicon dioxide.

Antimicrobial Effect

• Purpose: Inhibit microbial proliferation.
• Active compounds: Some ear cleaners contain potent antimicrobial components like chlorhexidine and parachlorometaxylenol (PCMX).

Contraindications and Side Effects

• Inflammation: Some cleaning fluids can cause inflammatory reactions, especially if introduced into the middle ear.
• Examples of fluids: Propylene glycol, DSS, carbamide peroxide, and triethanolamine often cause inflammation of the middle ear mucosa in normal dogs.
• Chlorhexidine: Generally regarded as ototoxic; ototoxicity usually depends on the concentration, formulation and presence of tympanic membrane.

How to Clean the Ear Canal

• Owner Instruction: Steps to clean, involving pulling the ear flap, applying medication to the ear canal entrance, gently manipulating and massaging the ear canal, and then allowing the animal to shake its head. Avoid using cotton tipped applicators because of the damage they can cause to the vertical ear canal.

General Pharmacology for Infectious Otitis (Ear Infections)

• Composition: Typically combine an antibiotic, antifungal, and glucocorticoid.
• Uses: Treatment of bacterial and Malassezia otitis.

Topical Antibiotics

• Types: Fluoroquinolones (enrofloxacin, orbifloxacin, marbofloxacin), aminoglycosides (gentamycin, amicacin, neomycin, tobramycin), and large spectrum penicillins (polymixina B).

Antimysotics against Malassezia

• Effectiveness: Topical antimycotics are very efficient.
• Examples: Miconazole, clotrimazole, posaconazole, and nistatin.

Ototoxicity

• Ototoxic Drugs: Polimixine B, Tobramycin, and Neomycin.
• Potentially Safe: Gentamycin and Amicacin. Ototoxicity could depend on formulation and the presence of the tympanic membrane
• Safe: Fluoroquinolones, anti-fungals.
• Important: The vehicle of the preparation can also be ototoxic.