How easily do topical antibiotics pass through tympanostomy tubes? - an invitro study

Background: Despite potential ototoxicity, eardrops containing aminoglycosi des remain in widespread use in the presence of indwelling tympanostomy tub es (grommets). It is unclear how readily they pass into the middle ear duri ng administration, nor whether this is affected by middle ear secretions. M aterials and methods: The trans-tympanic pressure required to force antibio tic solutions through a tympanostomy tube in an artificial middle ear model was investigated with six ototopical preparations and two sizes of tube. T o assess the effect of middle ear secretions, tympanostomy tubes removed fr om patients ears were investigated in addition to new tubes. The intra-cana l pressure generated during tragal massage was also measured. Results: Pres sures required for leakage of solutions differed significantly between solu tions (P = 0.001) and tube sizes, smaller lumen tubes requiring higher tran s-tympanic pressure for leakage to occur. The presence of middle ear secret ions reduced the pressure required for leakage of solution. Tragal massage generated pressures of over 20 cm of H2O which would be enough to force sol ution into the middle ear in all tube/solution combinations. Discussion: So me antibiotic solution is likely to leak into the middle ear during most ap plications of antibiotic solution. Although the risk is small, this suggest s the possibility of ototoxicity, previously demonstrated in animal experim ents. The relatively low incidence of this occurrence in clinical practice is thought to be related to inter-species anatomical variations. (C) 1999 E lsevier Science Ireland Ltd. All rights reserved.