COMPARISON OF DISTORTION-PRODUCT OAE GENERATION BETWEEN A PATIENT GROUP REQUIRING FREQUENT GENTAMICIN THERAPY AND CONTROL SUBJECTS

Although the animal models used to characterize aminoglycoside ototoxi city are well developed, the initial stages of the ototoxic process of this important group of antibiotics in humans are less well understoo d. A group that receives frequent aminoglycoside therapy are cystic fi brosis (CF) patients, who may receive cumulative doses of gentamicin o ver 200 g in their lifetime. Consequently they represent a group in wh ich it is particularly appropriate to monitor regularly auditory funct ion. In this preliminary study, 15 young (aged 9-18 years) CF patients had their pure tone thresholds measured over 0.25-12 kHz. Their disto rtion product otoacoustic emission (DPOAE) growth functions were also measured at f(2) = 2, 4 and 6 kHz with f(2)/f(1) = 1.22. These results were compared with those obtained from 36 control volunteers of simil ar age. Fourteen of the CF patients had normal hearing (pure tone audi ogram (PTA) thresholds less than or equal to 10 dB HL over 0.25-8 kHz) . In this group, there was a significant elevation of the stimulus lev els required to generate a 2f(1) - f(2) DPOAE less than or equal to 10 dB SPL at 4 kHz. This elevation may represent one of the earliest cha nges in outer hair cell performance caused by gentamicin, although it may also be due to the CF condition itself. Whilst this measurement al one cannot be taken to indicate any serious cochlear dysfunction, it m ay have some clinical use as an early indicator or marker of functiona l deficit in the cochlea.