Hitomi Higuchi

Ototoxicity of Burow solution on the guinea pig cochlea.

PURPOSE OF THE STUDY The aim of the present study was to evaluate the ototoxicity of Burow solution. PROCEDURES Compound action potentials (CAPs) of the eighth nerve were measured before and 30 minutes after the application of the Burow solution in the middle ear cavity. RESULTS Use of the original Burow solution (pH 3.5) for 30 minutes caused a significant reduction of click sounds. A 2-fold diluted Burow solution (pH 4.4) for 30 minutes caused no reduction in CAP threshold. Burow solution, pH adjusted to 4.5, caused no changes in CAP threshold at 30 minutes. At 24 hours, Burow solution (pH 3.5) caused complete abolition of CAP. CONCLUSIONS Burow solution is ototoxic in the guinea pig when applied in the middle ear cavity for 30 minutes or longer. In the clinical settings, it is advisable to avoid allowing the solution to contact the round window for extended times.

Ototoxicity of Gentian Violet on the Guinea Pig Cochlea

Purpose Gentian violet (GV) is an antimicrobial and antifungal agent that has been used widely to treat intractable discharge in the ear. The purpose of this report is to warn clinicians about the ototoxic effect of GV in the middle ear. Materials and Methods GV ototoxicity was evaluated by measuring compound action potentials (CAPs) in the VIIIth nerve in adult Hartley guinea pigs. The middle ear cavities of the animals were filled with GV solution (0.5% or 0.13%), and CAPs were measured after intervals of 5 and 30 minutes and 1, 2, 6, and 24 hours. After all measurements were completed, the temporal bones were harvested for histopathologic evaluation. Celloidin-embedded specimens were cut into 20-&mgr;m slices and examined using light microscopy. The bacteriostatic activity of GV was evaluated using a disk-diffusion assay. Results A 0.5% GV solution produced a mild elevation in the CAP threshold at 30 minutes, a greater reduction at 1 hour, and complete abolishment of CAP at 24 hours. A 0.13% GV solution caused mild elevation in the CAP threshold at 2 hours and severe elevation at 6 hours. Massive new bone formation was found in the middle ear cavity at 6 weeks. GV concentrations of 0.13% and 0.06% were effective against all bacteria tested, with the exception of Pseudomonas aeruginosa. Conclusions Although GV has marked antibacterial and antifungal activities, its use should be limited to the external ear canal. GV exerts an ototoxic effect in a concentration- and time-dependent manner, and so the use of this drug in the middle ear cavity is not recommended.

Differences in Acetic Acid Ototoxicity in Guinea Pigs are Dependent on Maturity

Objectives: The objective was to study if the difference exist in drug ototoxicity between less mature and mature guinea pigs. Methods: The matured animal group had a body weight of 400 g and the less mature animal group had a body weight of 200 g. After compound action potential of the eight cranial nerves was measured, the middle ear cavity was filled with acetic acid. Results: The less mature animal group was more sensitive to the acetic acid treatment than the more mature animal group. Conclusion: We suggest that a difference in ototoxicity of certain otic drop treatments may exist between pediatric and adult patients.

Modulation of somatosensory abilities and the feeling of ear fullness in patients with acute sensorineural hearing loss

OBJECTIVE Patients with acute sensorineural hearing loss (ASNHL) often complain of a feeling of ear fullness (FEF) that is similar to the sensation experienced during barometric pressure changes. This suggests that modulation of somatosensory abilities may relate to the manifestation of FEF, whereas it cannot simply be assumed that somatosensory abilities would be directly affected by ASNHL. To examine this possible relationship, we estimated somatosensory abilities of the tympanic membrane, and investigated the relationship between them and the manifestation of FEF. METHODS To estimate somatosensory abilities of the tympanic membrane, 83 new patients demonstrating unilateral sudden deafness were studied. The air pressure was loaded through an exclusive device on the external auditory canals in order to measure the minimum change in air pressure sensed by the subjects. The minimum pressure was defined as the minimum sensory threshold for air pressure loading (MSTAP; daPa). We estimated patients somatosensory abilities and inquired about their experiences with FEF at the first medical examination (point 1) and at the time a steady audiogram was obtained (point 2). We also estimated MSTAP in 65 volunteers (130 ears) with no history of ear diseases and compared their MSTAP with that of sudden deafness patients. RESULTS MSTAP values (-64.0±32.2daPa, 60.5±26.0daPa) on the affected side with both negative pressure and positive pressure measured at point 1 were significantly higher than those (-40.7±15.0daPa, 40.0±12.7daPa) obtained at point 2 in all sudden deafness patients (p=0.0001, p=0.0001). There was no difference between MSTAP values (-39.6±10.7daPa, 39.9±11.4daPa) in normal subjects and those obtained at point 2 in all sudden deafness patients. On the other hand, significant differences of MSTAP with negative pressures between the affected and unaffected sides at point 1 were seen in 32 patients, and manifestation of FEF showed an insignificant association in these 32 patients (p<0.05). CONCLUSION Modulation of somatosensory abilities in ASNHL seemed to be the best possible explanation for results, suggesting that a rise in MSTAP may somehow be associated with FEF. Although it cannot be verified by result of the current study, consideration of the previous literature suggests that the phenomenon may be caused by cross-modality of hearing and somatosensory abilities.