II. Quantitative Analytical Procedure

A statistical methodology has been established to describe and compare, quantitatively, the ototoxic effects of aminoglycoside antibiotics. Sampling techniques for obtaining reliable estimates of cell damage in the organ of Corti and the vestibular system are described in this paper. The relationship of drug dosage to the percentage of hair cell damage in each inner ear sensory region was expressed as the slope of the least-squares linear regression line and was tested to reject the null hypothesis (slope u = 0) at the 0.05 level of significance. It was determined that, in each of the cases discussed, dosage and damage correlated positively and that by repeated computations, each time controlling for one observed or measured variable, guinea pigs contributing skewed results could be eliminated on a rational basis. By this method of careful selection, statistically significant relationships have been established from the data.

III. Comparative Quantitative Analysis

Hypotheses to explain the selective ototoxicity of aminoglycoside antibiotics may be grouped into two categories: 1) a partition effect and 2) innate hair cell selectivity. The results of this study give evidence that, in fact, both mechanisms may interplay. This conclusion is induced from the observations that following the transtympanic administration of streptomycin, dihydrostreptomycin and neomycin: 1) All three drugs elicited nearly the same topographic pattern and degree of damage in the vestibular compartment. 2) All three drugs elicited nearly the same topographic pattern but widely different degrees of damage in the cochlear compartment (neomycin > > streptomycin > dihydrostreptomycin). 3) Neomycin caused the same devastating cochlear hair cell damage as reported for its systemic administration. 4) Dihydrostreptomycin was significantly more vestibulotoxic than cochleotoxic, and streptomycin was both significantly more cochleotoxic than vestibulotoxic and significantly more cochleotoxic than was dihydrostreptomycin. The latter observations are discussed with regard to contrasts with the literature reporting the drug effects following systemic administration.

IV. Influence of Vestibular Stimulation

Guinea pigs were given transtympanic dosages of neomycin followed by three hours of either vestibular stimulation or immobilization to test the hypothesis that inner ear hair cell membrane permeability is increased for drugs as a consequence of the transduction process. It was found, however, that neither the topographic pattern nor the degree of hair cell damage differed between the two groups. It is concluded that if the transduction process is accompanied by cell membrane permeability changes, the effect is not an increased susceptibility to neomycin toxicity. A measurable effect of stimulation was the significant decrease in the standard deviation of the mean dosage-damage response at each dosage level. This increase in reliability probably resulted from mixing of the inner ear fluids (especially in the vestibular compartment) which encouraged consistent dosages to the hair cells with each repeated trial. Finally, the impact of these findings on hypotheses related to the mechanism of selective ototoxicity is discussed briefly.

The Effect of Intratympanic Methylprednisolone and Gentamicin Injection on Ménière’s Disease

Objectives

To compare the efficacy of intratympanic injections of methylprednisolone (ITMP) and intratympanic injections of gentamicin (ITG) to control the symptoms of Ménière’s disease and to evaluate their effect on hearing level.

Study Design

A historical cohort study.

Setting

Tertiary referral center.

Subjects and Methods

Eighty-nine patients affected by Ménière’s disease were included in this study, of whom 47 were treated with ITG and 42 were treated with ITMP. Two periods of follow-up were considered: 0 to 6 months and 6 to 12 months after the intratympanic injections (ITI). Mean outcome measurements consisted of control of vertigo attacks, tinnitus, and aural fullness; pure-tone average (PTA); and speech discrimination score (SDS).

Results

The 2 groups had the same number of vertigo spells per month before ITI ( P = .883). Six to 12 months after ITI, 82.9% of the ITG group and 48.1% of the ITMP group achieved complete control of vertigo ( P = .004). There was better control of tinnitus and aural fullness with ITG than with ITMP ( P ≤ .002). The 2 groups had a statistically significant difference in hearing level before ITI ( P ≤ .001). This difference was no longer present 6 to 12 months after ITI ( P > .05).

Conclusion

Intratympanic injections of gentamicin are more efficient than ITMP in controlling the symptoms of Ménière’s disease. The 2 groups ended up without a difference in hearing level after ITI. According to these findings, administrating ITMP to control Ménière’s disease seems to be less beneficial than ITG.

Variability in the perilymphatic diffusion of gadolinium does not predict the outcome of intratympanic gentamicin in patients with Ménière's disease

OBJECTIVES/HYPOTHESIS

To assess the utility of imaging in planning intratympanic (IT) gentamicin (Gent) treatment in Ménière's disease (MD), we compared the dosage and outcomes of ITGent with the severity and extent of endolymphatic hydrops (EH), as evaluated by three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) sequence in a 3-T magnetic resonance imaging (MRI) unit, after IT gadolinium administration.

STUDY DESIGN

Retrospective review.

METHODS

A total of 18 patients (10 males and 8 females; age, 28-78 years; median age, 53.2 years) with definite MD participated in the investigation. The duration of the disease ranged from 8 months to 9 years (median, 2 years), with a prevalence of vertigo spells ranging from 0.8 to 8 per month (median, 2.2), as calculated in the last 6 months. A 3D-FLAIR MRI was performed 24 hours after IT injection of diluted gadobutrol. ITGent injection was performed within a variable period of time, from 1 week to 3 weeks after 3D-FLAIR MRI. The degree and extension of EH as evaluated by 3D-FLAIR MRI were compared with the number of injections necessary to cure vertigo attacks. Vertigo results, functional level scale modifications, variations in caloric excitability, and pure-tone average modifications.

RESULTS

No statistically significant correlation was observed between severity of EH and outcomes of ITGent administration.

CONCLUSIONS

The hypothesis of a reduced effect of Gent administered intratympanically in the presence of severe EH, owing to obstacled diffusion along the perilymphatic compartments, has not been confirmed in the present investigation.

Intratympanic gentamicin in monolateral Meniere’s disease: our experience

The aim of this study was to verify the efficacy of a modified Odkvist titration protocol of intratympanic gentamicin application in the control of vertigo attacks and the effects on the auditory and vestibular function in a group of 71 patients affected by monolateral MD resistant to medical therapy. All the patients underwent an intratympanic administration of a 1-ml solution containing 26.6 mg of gentamicin sulfate. The treatment protocol provided one to three injections for a total amount of gentamicin varying from 26.6 to 80 mg. Five days after the first gentamicin administration, cochlear and vestibular function tests were performed. The worsening of the PTA greater than 15 dB, the appearance of clinical signs of vestibulotoxicity such as imbalance or persistent spontaneous nystagmus beating away from the injected ear or of a "curative vertigo" were the criteria taken into consideration to stop the treatment. In the absence of any sign, a second and third injection were performed. The presence of an unchanged frequency of the attacks at least 3 months after the previous cycle was the parameter considered to perform a second or third cycle. Seventeen (24%) patients were submitted to a second cycle of therapy and two (3%) to a third cycle. After a mean follow-up period of 20.3 months (range: 3 to 48) all 71 patients experienced good control of the vertigo attacks: grade A in 46 cases and grade B in 25 cases according to the AAO-HNS CoHE criteria. The pure tone average (PTA) hearing threshold (500-3,000 Hz) worsened in 19 patients, improved in 5 and was unchanged in 47. On the basis of the experience acquired during the treatment, we progressively decreased the number of injections from 3/cycle to a 1-2/cycle of therapy. Moreover, in the later phase of the study re-injections were administered 1 or 2 weeks after the previous application and avoided in the presence of signs of depression of the vestibular and/or cochlear function. A residual caloric excitability was found in 30% of the cases. Vertigo control doesn't seem to be linked to the achievement of vestibular inexcitability. The marker of successful gentamicin treatment at short-term is the appearance of signs of curative vertigo and/or vestibular imbalance, and at long-term the disappearance of vertigo attacks.

Intratympanic gentamicin for the treatment of unilateral Meniere's disease

OBJECTIVE

To determine the efficacy of intratympanic gentamicin instillation as treatment of incapacitating unilateral Meniere's disease, using a predetermined regimen with a fixed dose.

STUDY DESIGN

A prospective study from a single institution between 1988 and 1998.

METHODS

One hundred fourteen patients were enrolled in this study. Gentamicin (26.7 mg/mL) was administered three times daily for 4 consecutive days. The Committee on Hearing and Equilibrium Guidelines for Reporting Treatment Results in Meniere's Disease of the American Academy of Otolaryngology and Head and Neck Surgery (1985) were used.

RESULTS

Comprehensive data were available for 90 individuals. Complete control of vertigo was achieved in 76 (84.4%), substantial control in 8 (9.0%), limited control in 2 (2.2%), and insignificant control in 4 (4.4%) patients. Disability scores at the end of 2 years were as follows: 76 patients (84.4%) had no disability, 5 (5.6%) had mild disability, 2 (22%) had moderate disability, and 7(7.8%) had severe disability. Caloric testing responses, as determined using electronystagmography, were as follows: 71% of the patients had an absent ice-water response, 16% had a positive ice-water response, and in 13% there continued to be present a bithermal response. Hearing was worse in 22 patients (25.6%), unchanged in 41 (48.2%), and improved in 22 (25.6%).

CONCLUSIONS

Intratympanic gentamicin administration using this particular protocol is an effective treatment option for patients with disabling unilateral Meniere's disease. Hearing loss is a distinct possibility, and patients should be advised accordingly.

Ototoxicity of topical otomicrobial agents

Topical antimicrobial solutions are used commonly for prevention or treatment of purulent otorrhea even though most solutions contain ototoxic agents. This study compares the cochlear and middle ear toxicity of cortisporin otic solution (COS), 0.3% gentamicin ophthalmic solution (GOS), benzalkonium chloride (0.026% and 0.05%), and 1.0% Ofloxacin, a new quinolone antibiotic. Saline 0.9% was used as a control. The agent was instilled daily for 7 days into the bulla of juvenile guinea pigs. The animals were sacrificed on the 14th day. The organ of Corti was examined using surface preparation light microscopy and scanning electron microscopy. The tympanic membrane (TM) and adjacent middle ear mucosa were examined with light microscopy. The average cochlear hair cell damage was 66% for COS, 6.5% for GOS, and 1% for Ofloxacin, benzalkonium and saline. COS and benzalkonium 0.05% produced moderate mucosal thickening and inflammation. However, this was not statistically different from the mild mucosal thickening produced by saline, GOS, Ofloxacin and 0.026% benzalkonium. There was statistically significant mild to moderate thickening of the TM for all agents compared to the saline control.

Intratympanic ototoxicity: influence of post-injection survival period

Many studies have been reported on the intratympanic ototoxicity of different drugs in animal models. The recovery periods of the animals following intratympanic drug applications varied among these studies. The present study compares the cochlear damage caused by intratympanic kanamycin following short (4 days) and long (30 days) post-injection survival periods, using the guinea pig as the animal model. The degree of cochlear damage 4 days after kanamycin injection was consistent among the tested animals. The degeneration was mainly confined to the outer hair cells and almost all inner hair were spared. The change 30 days after kanamycin injection was more variable among the animals and both inner and outer hair cells were damaged. This shows that, although the damage to the cochlea after intratympanic aminoglycoside injection is progressive, a short post-injection recovery period is suitable for comparative intratympanic ototoxicity studies.

Ototoxicity of otic drops applied to the middle ear in the chinchilla

Previous studies have shown that the application of topical otic drops to the external ear canals of animals with patent tympanostomy tubes may result in hearing impairment and cochlear hair cell loss. Otic drops are used in patients with tympanostomy tubes or tympanic membrane perforations and could have deleterious effects on the human membranous labyrinth. This report describes the inner ear damage that occurred after direct application of aminoglycoside-containing otic drops to the middle ears of experimental animals. The membranous labyrinths of 25 chinchillas were studied two days to five months after application of Cortisporin otic suspension (which contains neomycin, polymyxin B, hydrocortisone, and propylene glycol) to the middle ear cavity. Application of 0.5 ml of Cortisporin resulted in degeneration of all inner and outer hair cells throughout the cochlea, as well as severe damage to the stria vascularis. Moderate to severe degeneration of the vestibular receptor organs was also observed. The endolymphatic sacs showed dark-staining endolymph, cellular debris, and macrophages in the sac lumina, as well as increased activity of the epithelial lining.