Local drug deliveries to the inner ear have become widely used in clinical practice and many new therapies are being developed. However, most of our knowledge of drug pharmacokinetics in the ear is unreliable due to both the technical difficulties in obtaining pure perilymph samples and the highly variable perilymph drug levels produced by round window applications. In the past project period, we developed novel methods of perilymph sampling and highly controlled methods of drug delivery that, when combined, allow meaningful pharmacokinetic studies to be performed for the first time. The experimental studies in our first aim will use cationic and anionic markers to quantify the distribution of substances throughout the cochlear and vestibular systems, following direct injections from pipettes sealed into perilymph at different locations. The role of electrical charge in determining whether substances enter endolymph will be studied. Concentration measurements in vivo will allow the major solute distribution and elimination properties to be quantified and will further validate measurements from fluid sampling procedures. When we understand the basic processes contributing to distribution and elimination from the ear, pharmacokinetic studies of the clinically relevant drugs gentamicin (a cation) and dexamethasone (an anion) will be performed using sequential sampling methods. The pharmacokinetics and pharmacodynamics of the anionic drug salicylate will also be studied, as an agent causing transient sensitivity changes of the ear that can be used as an indirect measure of drug distribution.
A second aim will focus on additional factors influencing perilymph drug levels when the drugs are applied intratympanically. This includes study of the rate of drug elimination from the middle ear and how the applied volume affects perilymph concentration. The merits of volume stabilized (gels) or timed release (gel or PLGA nanoparticles) delivery of drugs to the cochlea will be evaluated. In conjunction with these experimental studies, comprehensive 1-D, anatomically based, mathematical models of drug distribution in the fluid and tissue spaces of animal and human ears will be developed. The enhanced models will permit complex experimental protocols to be interpreted quantitatively and will allow realistic prediction of drug distribution patterns in humans. Models will be made available to other groups in the field, permitting quantitative interpretation of a variety of animal and human data. Results from these projects will provide a basic scientific foundation for physiologic studies utilizing drug applications to the ear and will allow the delivery of drugs or other substances to the ears of humans to be optimized for specific purposes.

Public Health Relevance

In many cases, ears affected by diseases would benefit from treatments using locally applied drugs. At present, drug delivery protocols are developed by trial and error in humans, sometimes to the detriment of the patient. This project seeks to develop an understanding of pharmacokinetics in the ear that will, in conjunction with computer models, allow drug treatment protocols to be scientifically based.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC001368-21
Application #
8220904
Study Section
Auditory System Study Section (AUD)
Program Officer
Cyr, Janet
Project Start
1992-01-01
Project End
2015-02-28
Budget Start
2012-03-01
Budget End
2013-02-28
Support Year
21
Fiscal Year
2012
Total Cost
$312,664
Indirect Cost
$106,964
Name
Washington University
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
068552207
City
Saint Louis
State
MO
Country
United States
Zip Code
63130
Eckhard, A; Müller, M; Salt, A et al. (2014) Water permeability of the mammalian cochlea: functional features of an aquaporin-facilitated water shunt at the perilymph-endolymph barrier. Pflugers Arch 466:1963-85
Lichtenhan, J T; Hartsock, J J; Gill, R M et al. (2014) The auditory nerve overlapped waveform (ANOW) originates in the cochlear apex. J Assoc Res Otolaryngol 15:395-411
Plontke, Stefan K; Glien, Alexander; Rahne, Torsten et al. (2014) Controlled release dexamethasone implants in the round window niche for salvage treatment of idiopathic sudden sensorineural hearing loss. Otol Neurotol 35:1168-71
Hahn, Hartmut; Salt, Alec N; Schumacher, Ulrike et al. (2013) Gentamicin concentration gradients in scala tympani perilymph following systemic applications. Audiol Neurootol 18:383-91
King, E B; Hartsock, J J; O'Leary, S J et al. (2013) Influence of cochleostomy and cochlear implant insertion on drug gradients following intratympanic application in Guinea pigs. Audiol Neurootol 18:307-16
King, E B; Salt, A N; Kel, G E et al. (2013) Gentamicin administration on the stapes footplate causes greater hearing loss and vestibulotoxicity than round window administration in guinea pigs. Hear Res 304:159-66
Salt, Alec N; King, Elisha B; Hartsock, Jared J et al. (2012) Marker entry into vestibular perilymph via the stapes following applications to the round window niche of guinea pigs. Hear Res 283:14-23
Salt, Alec N; Hartsock, Jared; Plontke, Stefan et al. (2011) Distribution of dexamethasone and preservation of inner ear function following intratympanic delivery of a gel-based formulation. Audiol Neurootol 16:323-35
Salt, Alec N; Plontke, Stefan K (2010) Endolymphatic hydrops: pathophysiology and experimental models. Otolaryngol Clin North Am 43:971-83
Salt, Alec N; Hullar, Timothy E (2010) Responses of the ear to low frequency sounds, infrasound and wind turbines. Hear Res 268:12-21

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