Transtympanic versus sustained-release administration of gentamicin: kinetics, morphology, and function

Area of Science:

• Ototolaryngology
• Pharmacology
• Inner Ear Therapeutics

Background:

• Transtympanic gentamicin is used for Meniere's disease, but optimal dosing and delivery remain unclear.
• Understanding gentamicin's inner ear kinetics is crucial for refining treatment strategies.
• This study investigates gentamicin pharmacokinetics and its impact on inner ear function and morphology.

Purpose of the Study:

• To compare the inner ear kinetics of transtympanic versus sustained-release gentamicin delivery.
• To correlate gentamicin kinetics with functional (hearing, balance) and morphological outcomes.
• To inform optimal clinical application of local gentamicin therapy for Meniere's disease.

Main Methods:

• A basic science study using an animal model (chinchillas).
• Gentamicin administered via transtympanic injection or sustained-release device to the right ear.
• Perilymph gentamicin levels, hearing, balance function, and inner ear morphology assessed at set time points.

Main Results:

• Transtympanic gentamicin showed high peak levels with rapid decline and high variability.
• Sustained-release gentamicin demonstrated a prolonged plateau phase with lower peak levels and less variability.
• Both methods caused spiral ganglion damage; transtympanic delivery showed denser staining and more variable hearing loss.
• Sustained-release delivery resulted in predictable, universal hearing loss by 72 hours.

Conclusions:

• Significant differences exist in perilymph gentamicin kinetics between transtympanic and sustained-release delivery.
• High early gentamicin peaks from transtympanic therapy may damage the spiral ganglion, causing variable hearing loss.
• Sustained-release gentamicin provides reliable delivery, leading to consistent hearing loss and reduced morphological variation.