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Effects of chronic tobramycin treatment on distortion product otoacoustic emissions
B Katbamna1, D N Homnick, J H Marks
1Department of Speech Pathology and Audiology, Western Michigan University, Kalamazoo 49008-3825, USA.
Insights
Distortion product otoacoustic emission (DPOAE) latencies and response growth detection thresholds are sensitive indicators of early cochlear ototoxicity from tobramycin treatment. DPOAE amplitudes may not detect these subtle changes in hearing function.
Area of Science:
- Ototolaryngology
- Audiology
- Pharmacology
Background:
- Chronic tobramycin treatment, an aminoglycoside antibiotic, is known to cause ototoxicity.
- Early detection of ototoxicity is crucial for preserving hearing function.
Purpose of the Study:
- To investigate the effects of chronic tobramycin on distortion product otoacoustic emission (DPOAE) latencies and response growth detection thresholds.
- To determine the sensitivity of these DPOAE features to early ototoxic damage.
Main Methods:
- Six groups of children and young adults with cystic fibrosis (CF) and normal hearing were tested.
- CF patients received varying cumulative doses of tobramycin.
- Distortion product otoacoustic emissions (DPOAEs) were measured, focusing on latencies and response growth detection thresholds.
Main Results:
- Significant changes in DPOAE latencies and growth function thresholds were observed in CF patients treated with tobramycin, despite normal audiometric profiles.
- Low-to-moderate tobramycin doses prolonged DPOAE latencies, while higher doses reduced them.
- Response growth detection thresholds at high frequencies were elevated in all tobramycin-treated CF groups.
Conclusions:
- DPOAE latencies and response growth detection thresholds are more sensitive to early cochlear ototoxicity from chronic tobramycin treatment than DPOAE amplitudes.
- These DPOAE features may serve as effective monitoring tools for early ototoxicity.
- Findings are tentative due to small sample size.
Objective:
To investigate the effects of chronic tobramycin treatment on distortion product otoacoustic emission (DPOAE) latencies and response growth detection thresholds in human subjects to determine the sensitivity of these DPOAE features to ototoxic damage.
Design:
Six groups of children in two different age ranges were tested: three groups in the 7 to 14 yr age range, i.e., six children with normal hearing, four cystic fibrosis (CF) patients who received no aminoglycosides, and eight CF patients who received low- to moderate-cumulative doses of tobramycin (< 1250 mg/kg) for respiratory infections; and three groups of five subjects each in the 15 to 23 yr age range, i.e., the healthy group and the CF groups that received low- (< 285 mg/kg) and moderate-(1000 to 2000 mg/kg) cumulative drug dosages. The aggregate drug dosages compiled longitudinally over the past 5 yr were used to group the drug-treated CF patients. All subjects showed normal audiometric profiles (< or = 25 dB HL in the conventional frequency region and age-appropriate thresholds as described by Osterhammel and Osterhammel [1979] in the high-frequency region) and DP-grams (absolute DPOAE and noise amplitudes being consistent with the normative data obtained with the CUBeDIS system at this institution).
Results:
Even though the audiometric profiles and DP-grams of all drug-treated CF groups were identical to their healthy counterparts, the DPOAE latencies and growth function thresholds showed significant changes. Whereas low and low-to-moderate doses of tobramycin were related to DPOAE latency prolongations, higher cumulative drug doses of 1000 to 2000 mg/kg produced significant reductions in DPOAE latencies. Response growth detection thresholds at high frequencies showed significant elevations in all CF patient groups treated with tobramycin, regardless of drug dosages, as compared with the control subjects.
Conclusions:
DPOAE amplitudes may not reflect the earliest changes produced by chronic aminoglycoside treatment, suggesting that cochlear ototoxicity may be more effectively monitored through the assessment of latencies and response growth detection thresholds. These findings pertain at least to the early stages of ototoxicity development, specifically during chronic tobramycin treatment. In light of the small sample size, however, these outcomes must be considered as tentative.
