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How easily do topical antibiotics pass through tympanostomy tubes?--an in vitro study
1Department of Otorhinolaryngology, Southmead Hospital, Bristol, UK.
Background:
Despite potential ototoxicity, eardrops containing aminoglycosides remain in widespread use in the presence of indwelling tympanostomy tubes (grommets). It is unclear how readily they pass into the middle ear during administration, nor whether this is affected by middle ear secretions.
Materials And Methods:
The trans-tympanic pressure required to force antibiotic solutions through a tympanostomy tube in an artificial middle ear model was investigated with six ototopical preparations and two sizes of tube. To assess the effect of middle ear secretions, tympanostomy tubes removed from patients ears were investigated in addition to new tubes. The intra-canal pressure generated during tragal massage was also measured.
Results:
Pressures required for leakage of solutions differed significantly between solutions (P=0.001) and tube sizes, smaller lumen tubes requiring higher trans-tympanic pressure for leakage to occur. The presence of middle ear secretions reduced the pressure required for leakage of solution. Tragal massage generated pressures of over 20 cm of H20 which would be enough to force solution into the middle ear in all tube/solution combinations.
Discussion:
Some antibiotic solution is likely to leak into the middle ear during most applications of antibiotic solution. Although the risk is small, this suggests the possibility of ototoxicity, previously demonstrated in animal experiments. The relatively low incidence of this occurrence in clinical practice is thought to be related to inter-species anatomical variations.
Insights
Aminoglycoside eardrops may leak into the middle ear through tympanostomy tubes (grommets), especially with secretions present. Tragal massage significantly increases this risk, potentially causing ototoxicity.
Area of Science:
- Otolaryngology
- Pharmacology
- Biomedical Engineering
Background:
- Aminoglycoside eardrops are commonly used with tympanostomy tubes despite ototoxicity concerns.
- The passage of eardrops into the middle ear via these tubes is not well understood.
- The influence of middle ear secretions on eardrop passage is unclear.
Purpose of the Study:
- To quantify the pressure required for antibiotic solutions to pass through tympanostomy tubes.
- To investigate the impact of middle ear secretions on this passage.
- To measure pressures generated by tragal massage.
Main Methods:
- An artificial middle ear model was used to test six ototopical preparations and two tympanostomy tube sizes.
- Tubes from patients with middle ear secretions were compared to new tubes.
- Intra-canal pressure from tragal massage was recorded.
Main Results:
- Leakage pressures varied significantly by solution and tube size; smaller lumens required higher pressure.
- Middle ear secretions reduced the pressure needed for solution leakage.
- Tragal massage generated pressures sufficient to force solutions through all tested tubes.
Conclusions:
- Some leakage of antibiotic solution into the middle ear is probable during administration.
- This leakage poses a potential, albeit small, risk of ototoxicity.
- Clinical rarity may be due to inter-species anatomical differences.