Ototoxicity: a clinical review

[Tinnitus in a Patient Treated by Bleomycin for Kaposi's Sarcoma]

We describe a case of tinnitus occurred during a bleomycin monotherapy for Kaposi's sarcoma.

Ototoxicity: the hidden menace

Otolaryngology, although considered a surgical specialty, also covers many diseases that are not cured by surgery. These are treated medically and thus the otolaryngologist should have a good knowledge of drug treatments. It also entails ability to recognize, when an ENT symptom may be caused by one of the patient's medications, particularly as this is easily remedied by changing the drug. Although most of us know the common drugs that can cause otological side effects, there are many others that we may not be aware of. Here we have tried to consolidate a list of some commonly used drugs having otological side effects.

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

Maturation of the human cochlear amplifier: distortion product otoacoustic emission suppression tuning curves recorded at low and high primary tone levels

The cochlear amplifier shows level-dependent function and works optimally at low levels. For this reason, manipulation of stimulus level is a route through which the human cochlear amplifier can be investigated in a noninvasive manner. Distortion product otoacoustic emissions (DPOAEs) evoked as a function of stimulus level provide a tool for exploration of human cochlear amplifier function and, when applied to neonates, for investigation of cochlear maturation. The current experiment generated 2f1-f2 DPOAE ipsilateral suppression tuning curves (STCs) at three primary tone levels and five f2 frequencies in a large group of premature and term neonates and adults. The differences between tuning generated with low- and high-level primary tones was measured to provide a gross estimate of the "tuning enhancement effect" attributed to the cochlear amplifier. Other features of the DPOAE suppression tuning curves were measured as well. Consistent with previous reports, at 1500 and 6000 Hz, STCs were narrower, with a steeper slope on the low-frequency flank of the tuning curve in premature neonates versus adults. Additionally, only DPOAE STCs from adults and term neonates became markedly broader and more shallow when recorded with high-level primary tones. It has been hypothesized that the excessive narrowness of suppression tuning and the absence of a level effect on DPOAE STCs recorded in premature neonates reflects a subtle immaturity in cochlear amplifier function just prior to term birth.

Behavioural evidence for recovery of auditory function in guinea pigs following kanamycin administration

Deterioration followed by recovery of behavioural absolute threshold and frequency selectivity has been observed in guinea pigs following kanamycin administration of 200 mg/kg body weight daily for 16 days. Deterioration in function consistently follows a high-to-low frequency pattern and recovery generally occurs at the lowest of the high (8-32 kHz) frequencies affected. The degree of recovery is related to the magnitude of the threshold elevation; where large (40-45 dB) elevations occur initially, the process appears to be partial since threshold recovers only to within 5-12 dB of pre-administration levels. In instances where smaller threshold elevations (5-20 dB) take place initially, recovery can sometimes be complete. However, when threshold elevations of over 50 dB occur, no recovery is apparent. Recovery is relatively slow, taking place over periods of up to 100 days post-kanamycin administration. Hair cell counts have established that the threshold elevation which remains in instances of partial recovery is not related to a reduction in hair cell numbers at the light microscope level.

Drug-induced ototoxicity. Pathogenesis and prevention

Ototoxicity is a disabling adverse effect of several widely used classes of drugs, such as diuretics, anti-inflammatory agents, antineoplastic agents and aminoglycoside antibiotics. High-dose therapy with either diuretics or anti-inflammatory agents is primarily associated with acute and transient impairment of hearing or tinnitus. In contrast, long term treatment with antineoplastic agents or aminoglycoside antibiotics is typically associated with delayed and irreversible loss of hearing; lesion in the organ of Corti include the destruction of auditory sensory cells. Vestibular function can also be compromised by ototoxic drugs. Occasional cases of ototoxicity have been reported for a variety of other therapeutic compounds and environmental toxins. In addition, the simultaneous administration of multiple agents which are potentially ototoxic can lead to synergistic loss of hearing. Exposure to loud noise may also potentiate the hearing loss due to cochleotoxic drugs. Ototoxic agents can impair the sensory processing of sound at many cellular or subcellular sites. However, the molecular mechanisms of ototoxicity have not been established for most of these drugs, and structure-toxicity relationships have not been determined. It has therefore been difficult to predict the ototoxic potential of new drugs, and rational approaches to the prevention of ototoxicity are still lacking. The clinical and experimental features of ototoxicity are reviewed for several classes of drugs, with an emphasis on current knowledge of the mechanism and the possibilities for the prevention of ototoxicity for each.

The histological effects on the guinea pig external ear of several constituents of commonly used aural preparations

Medicament contact dermatitis can be troublesome in external ear disease. In this work the effects on the guinea pig external ear of instillation twice daily for 3 weeks of benzalkonium chloride, Cerumol, gentamicin, the pharmaceutical base for Gentisone HC, hydrocortisone and propylene glycol were studied using light microscopy, thickness measurements of tympanic membrane and meatal epidermis, and the mitotic index of meatal epidermis. Benzalkonium chloride induced severe inflammatory changes and markedly increased the thickness measurements and meatal mitotic index. Cerumol also increased the thickness measurements and the mitotic index; there was additionally low grade chronic inflammation in the dermis. Prophylene glycol increased the mitotic index and thickness measurements though no signs of inflammation were seen. Other compounds did not produce significant changes except that hydrocortisone reduced the mitotic index. Contact dermatitis to benzalkonium chloride may be important in persistent ear disease. Cerumenolytic agents ought not to be used for prolonged periods or as prophylaxis.

The ototoxicity of repetitive chronic aminoglycoside administration. An experimental study

To determine whether previous exposure to an aminoglycoside antibiotic would predispose an individual to more severe ototoxic reactions upon subsequent administration, guinea pigs were given up to three courses of gentamicin at a dose of 50 or 100 mg/kg. Each course was separated by a period of 4 weeks, and animals were killed 4 weeks after the date of last injection. Cochlear pathology was assessed by the surface preparation technique and phase contrast microscopy. Detailed counts of sensory hair cell populations were recorded and statistically analysed. No significant ototoxic hair cell loss occurred following the repetition of 50 mg/kg. At 100 mg/kg, repetitive administration produced a significant and cumulative destruction of the most basal outer and inner hair cells. Using this protocol, it was concluded that if the initial exposure proved ototoxic, further administration of gentamicin increased subsequent sensory hair cell loss.

A case of profound hearing impairment following the prolonged use of framycetin ear drops

A report is presented of a patient with profound hearing impairment after eleven months' treatment with framycetin ear drops. It emphasizes the risk of prolonged use of these ear drops.

"Is magnesium depletion the reason for ototoxicity caused by aminoglycosides?"

Aminoglycoside antibiotic drugs may cause ototoxicity and nephrotoxicity. Our hypothesis postulates that aminoglycosides cause ototoxicity by a mechanism of magnesium depletion in the hair cells of the cochlea. The same mechanism maybe responsible for nephrotoxicity caused by aminoglycosides.

Patterns of cochlear degeneration following gentamicin administration in both old and young guinea pigs

This study aims to compare experimentally the effect of gentamicin administration on the cochleae of guinea pigs of different ages. While it is frequently cited that age may represent a predisposing factor towards aminoglycoside ototoxicity in clinical reports, little experimental work has been carried out on this topic. Two groups of albino guinea pigs, either 4 weeks or 24 weeks old, were used. Animals were injected subcutaneously for 10 consecutive days with gentamicin at a dose of either 50 or 125 mg/kg/day, or with an equivalent volume of saline to act as controls. The survival period after the last injection was either 4 or 12 weeks. On being killed, both bullae were removed and fixed in osmium tetroxide, and prepared of phase-contrast microscopy by the surface preparation technique. The entire hair cell population of one cochlea from each animal was recorded onto cochleograms, enabling detailed graphical and statistical analysis. Both age groups display extremely similar patterns of outer and inner hair cell loss at the higher dose; the lower dose of gentamicin was not ototoxic in this study. Hair cell loss is predominantly basal, and tends to be maximally concentrated in two areas of the base of the cochlea. While mortality is much higher in the older animals, there is no difference in the response of the two age groups to the ototoxic effects of gentamicin.

Pure-tone and speech intelligibility disturbances in patients with ototoxic disorders

The prevalence and severity of hearing impairment caused by ototoxic drugs are surprisingly high. This emphasizes the importance of the questions arising from the treatment. In 33.7% of the cases, the hearing impairment caused by ototoxic antibiotics was of severe degree and in 25.4%, it was extremely severe. Parenteral, topical or oral administration of aminioglycoside antibiotics is dangerous. Because of the very poor speech intelligibility, most probably not only the spiral organ but the vestibulocochlear nerve and the higher auditory pathways are also affected by these antibiotics. In some cases, the severe distortion in sound perception cannot be compensated even by a hearing aid of the best quality, and lip-reading which was advised occasionally was without any result. To prevent these toxic effects, these drugs should be administered very parsimoniously and then under very strict conditions and close control.

Aminoglycoside ototoxicity in the human

One hundred thirty-eight patient courses of tobramycin (tobra) and gentamicin (genta) were prospectively monitored for ototoxicity using weekly audiograms and electronystagmograms. Twice weekly drug serum levels and kidney function tests were determined. A pre, during, and post-therapy history was obtained and the results were analyzed to determine significant parameters of ototoxicity. Statistical analysis of the data was performed using SPSS on an IBM 370/3033 computer. Tobra showed less toxicity than genta but only the difference in vestibular toxicity was statistically significant. Significant associations with toxicity included the patient developing a high temperature, total dose, low hematocrit for tobra, high hematocrit for genta, high creatinine clearance with cochlear toxicity, high creatinine with nephrotoxicity, poor condition or critically ill, and duration of therapy greater than 10 days. Non-significant parameters included dose rate (mg/kg), serum levels, age, prior noise exposure, prior aminoglycosides, prior ear infections, non-aminoglycoside ototoxic drugs, underlying disease, or total number of high risks present. Ototoxicity was independent of nephrotoxicity.