How easily do topical antibiotics pass through tympanostomy tubes?—an in vitro study

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 H 2O 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.