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Estimation of perilymph concentration of agents applied to the round window membrane by microdialysis
Brian A Hunter1, Seahyoung Lee, Rick M Odland
1Department of Otolaryngology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
Objective:
The round window membrane (RWM) is known to be permeable to various biological substances. Application of biological substances to the RWM has been shown to affect inner ear fluid composition and damage hair cells, resulting in functional changes RWM instillation of gentamicin, a preferentially vestibulotoxic aminoglycoside, is used as a therapeutic treatment for patients with intractable vertigo and is gaining acceptance as a chemical vestibular ablation agent, despite considerable variations in the incidence and severity of hearing loss associated with gentamicin. Clearly, the susceptibility of vestibular and auditory hair cells to the ototoxic effects of gentamicin is not well understood. The aim of this study was to understand the kinetics of urea and methylene blue instilled into the inner ear space through the RWM and to establish a method for determining the optimal dosage for the treatment of inner ear disorders.
Material And Methods:
We used inner ear microdialysis to quantify changes in perilymph concentration of low molecular weight agents applied to the RWM in a chinchilla model.
Results:
Preliminary results after placement of a microdialysis probe and application of a low molecular weight marker (urea) to the RWM were extrapolated from a time versus concentration plot from dialysates sampled over a 3-min interval using modifications of standard microdialysis equations for estimation of in vivo recovery. Our data suggest that inner ear microdialysis can be used to measure the pharmacokinetics of a low molecular weight agent within the perilymphatic space without the need for repeated direct sampling.
Conclusion:
Inner ear microdialysis may be a useful method for establishing a therapeutic dosage for ototoxic agents used in the treatment of inner ear disorders.
Insights
Inner ear microdialysis effectively measures drug concentrations in the inner ear fluid. This method helps determine optimal dosages for treatments like gentamicin, minimizing hearing loss risks.
Area of Science:
- Ototoxicity research
- Inner ear drug delivery
- Pharmacokinetics
Background:
- The round window membrane (RWM) allows substances into the inner ear, impacting fluid composition and hair cells.
- Gentamicin treatment for vertigo via RWM instillation causes variable hearing loss, indicating a need to understand ototoxicity.
- Optimal dosing for inner ear treatments remains unclear due to variability in hair cell susceptibility.
Purpose of the Study:
- To investigate the kinetics of urea and methylene blue instilled through the RWM into the inner ear.
- To develop a method for determining optimal dosages for treating inner ear disorders.
- To understand the susceptibility of vestibular and auditory hair cells to gentamicin ototoxicity.
Main Methods:
- Utilized inner ear microdialysis in a chinchilla model.
- Quantified perilymph concentration changes of low molecular weight agents applied to the RWM.
- Extrapolated preliminary results using time-concentration plots and modified microdialysis equations for in vivo recovery estimation.
Main Results:
- Demonstrated that inner ear microdialysis can measure low molecular weight agent pharmacokinetics in perilymph.
- Showed that repeated direct sampling is not necessary for pharmacokinetic measurement.
- Established a method for estimating in vivo recovery of instilled agents.
Conclusions:
- Inner ear microdialysis is a viable method for pharmacokinetic studies of inner ear drug delivery.
- This technique may aid in establishing optimal therapeutic dosages for ototoxic agents.
- Further research can refine dosage determination for treatments like gentamicin, potentially reducing hearing loss.