Robert E. Brummett

Detection of ototoxicity from drugs applied topically to the middle ear space

This paper summarizes data obtained from two separate studies done in our laboratory. Both studies were done to investigate the possibility that drugs commonly applied to the middle ear space could be the cause of sensori‐neural hearing loss. The two drugs that were felt to be the most likely candidates for the studies were neomycin and polymyxin B. In the neomycin study, the various drug concentrations were administered three times a day for four weeks. In the polymyxin B study, the administration was three times a day for two weeks. Cochlear function was evaluated electrophysiologically and by examination of surface preparations of the organ of Corti.

The Delayed Effects of Ethacrynic Acid on the Stria Vascularis of the Guinea Pig

Guinea pigs were administered 40 mg ethacrynic acid per kg b.wt. and sacrificed at 30-48 minutes, 3-4 hours, 2 or 7 days post-drug. Cochlear potentials (EP and CP) were monitored before sacrifice. At 30-48 minutes, the potentials had decreased considerably, and a marked edema plus cytological changes were visible in the stria vascularis. The potentials had recovered to about 75% of their original value at 3-4 hours; some cell recovery was visible, but the edema was still present. Potentials recorded from the basal turn were normal at 2 and 7 days, although some strial cells showed deterioration.

Ototoxic Effects of the Interaction Between Kanamycin and Ethacrynic Acid: Cochlear infrastructure Correlated with Cochlear Potentials and Kanamycin Levels

The effects of the interaction between kanamycin (KAN) and ethacrynic acid (EA) on the ultrastructure of the guinea pig cochlea were studied 3, 4, 6, and 24 hours following administration of EA (40 mg/kg) to animals pretreated 2 h earlier with KAN (400 mg/kg). Appropriate saline (SAL) controls were included giving 4 treatments: KAN/EA, KAN/SAL, SAL/EA and SAL/SAL. The outer hair cells of the organ of Corti showed nuclear and plasma membrane changes at 3 h and were completely destroyed at 24 h. The inner hair cells were unaffected. Severe swelling was seen in the stria vascularis of both KAN/EA and SAL/EA animals at 3 h and was gone by 24 h. KAN/EA had a greater effect on the stria than had SAL/EA. These results were consistent with the time course of the effect of the drugs on the a.c. and d.c. endocochlear potentials. KAN concentrations in perilymph were unaffected by treatment with EA.

COCHLEAR DAMAGE RESULTING FROM KANAMYCIN AND FUROSEMIDE

Permanent cochlear damage has been shown to occur in guinea pigs following the combined administration of kanamycin and furosemide. At the doses used, only a transient effect was measured with furosemide alone and no effect was detectable with kanamycin alone. This interaction results when a single subcutaneous dose of 400 mg/kg of kanamycin is followed in 2 hours by a single intravenous dose of furosemide. The dosage range for furosemide was 50 mg/kg for a just-detectable effect to 100 mg/kg for a very severe effect. Damage to the cochlea was ascertained by measures of the a.c. cochlear potential as well as surface preparation histology.

Comparative ototoxicity of bumetanide and furosemide when used in combination with kanamycin.

Abstract: The ototoxicity of bumetanide and furosemide was compared in Topeka strain guinea pigs pretreated with kanamycin. The animals, anesthetized with pentobarbital, received a single dose of 400 mg/kg kanamycin subcutaneously and the diuretics via indwelling catheter in the jugular vein 2 hours later. Ototoxic drug effects were determined by measuring the electrophysiological responses of the cochlea to sound stimuli and by determining the presence or absence of cochlear sensory hair cells from the organ of Corti. Both bumetanide and furosemide produced permanent alteration of cochlear activity in the kanamycin‐pretreated animals. The ototoxic effect of bumetanide is five times that of furosemide on a milligram‐for‐milligram basis. The ototoxic potential of bumetanide is one eighth that of furosemide when the doses are adjusted for diuretic potency difference between the two diuretics.

Combined effects of noise and neomycin. Cochlear changes in the guinea pig.

Cochlear damage resulting from the combination of neomycin with acoustic overstimulation was investigated in guinea pigs. Four groups of animals received subcutaneous injections and exposure to broad band noise daily for 7 days, as follows: I. Neomycin (200 mg/kg) followed by 10 hours of noise at 115 dB SPL; II. Saline followed by 115 dB noise: III. Neomycin followed by low intensity noise (45 dB as an acoustic control); or IV. Saline followed by 45 dB noise. After a 30 day stabilization period, each ear was examined electrophysiologically and histologically. Measures of cochlear integrity included AC cochlear potentials from 100 Hz through 20 kHz as well as outer hair cell (OHC) counts. A marked interaction leading to augmentation of damage was found when neomycin was combined with 115 dB noise (Group I). Losses in cochlear sensitivity, averaged across all frequencies, amounted to 62 dB in Group I, whereas the averaged losses for Groups II and III were only 16 dB and 17 dB respectively. Loss of OHCs was close to 100% in Group I, while OHC losses were only 17% in Group II and 26% in Group III.

The Relationship Between the Cytotoxicity of Kanamycin and Ethacrynic Acid for Mammalian Cells in Vitro and Their Ototoxicity in Vivo

Dose-effect curves for inhibition of growth of P388/P mouse lymphoma cells by ethacrynic acid and kanamycin used alone and in combination were determined in vitro. Ethacrynic acid was 600 times more potent than kanamycin and combinations of the drugs resulted in overall additive effects. These results were compared with known dose-effect data on the ototoxicity of these drugs in vivo. Kanamycin was highly selective in its toxicity for cochlear hair cells compared to cultured cells. The dose-effect data for ethacrynic acid was coincident with that reported for functional and biochemical effects on the cochlea following perilymphatic perfusion with the drug. The potentiation observed following the ototoxic interaction the two drugs in vivo was not observed following combinations of the drugs in vitro.

The Ototoxic Interaction of Viomycin, Capreomycin and Polymyxin B With Ethacrynic Acid

The ototoxic interaction between the aminoglycoside antibiotics (streptomycin, kanamycin, etc.) and the loop-inhibiting diuretics (ethacrynic acid, furosemide and bumetanide) has been well documented. This interaction causes extensive destruction of the hair cells of the cochlea. Brummett et al. (1974) demonstrated that this interaction did not occur with the non-loop-inhibiting diuretics and kanamycin. The present study was undertaken to determine if antibiotics other than the aminoglycosides could produce the ototoxic interaction when combined with a loop-inhibiting diuretic. Three antibiotics-viomycin, capreomycin, and polymyxin B- when given with ethacrynic acid were found to produce cochlear hair cell damage that was similar to that produced by aminoglycoside antibiotics administered with ethacrynic acid. Therefore, the interaction appears to be specific to the loop-inhibiting diuretics but not specific for the aminoglycoside antibiotics.

The Effects of Low Dose Ethacrynic Acid on the Guinea Pig Cochlea with Special Reference to Normal Variations in the Stria Vascularis

A controlled study of the effects of ethacrynic acid (5 mg/kg/day) vs. saline for 7 days on the guinea pig cochlea is described. The a.c. cochlear potential, d.c. endocochlear potential, Preyer pinna reflex, number of hair cells and ultrastructure of the cochlear duct were studied as indices of cochlear integrity. There were no differences between control and experimental groups in any of these indices. An unexpectedly wide variation in the histologic and cytologic appearance of the normal stria vascularis at the light and electron microscopic levels is described.