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

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.

The sensitive period for induction of susceptibility to audiogenic seizures by kanamycin in mice

It has been found that administration of kanamycin (400 mg/kg daily) for 5 days was highly effective in inducing susceptibility to audiogenic seizures in BALB/c mice, if the drug was administered between the age of 10-14 postnatal days. The same drug dosage administered between the age of 5-19, 15-19, or 20-24 postnatal days was found to be ineffective. Since induction of seizure susceptibility is highly correlated with the degree of cochlear damage produced by either ototoxic drugs or noise, it was suggested that the age of 10-14 postnatal days could be the most sensitive period for the ototoxic effect of kanamycin.

The ototoxicity of hydroxygentamicin, a new aminoglycoside antibiotic, in guinea pigs

The comparative ototoxicity of hydroxygentamicin (Win 42,122-2), a new aminoglycosidic antibiotic, gentamicin and kanamycin was evaluated in guinea pigs by assessment of the Preyer (pinna) reflex response to pure tone frequencies ranging from 2.5 to 20.0 KHz, and by histologic examination of surface preparations of the organ of Corti. Daily subcutaneous administration of 80.0 mg/kg of gentamicin or 240.0 mg/kg of kanamycin to groups of six guinea pigs for 18 to 45 days resulted in loss of the Preyer reflex in all animals. The Preyer reflex was retained in 5 of 6 guinea pigs given 80.0 mg/kg/day of hydroxygentamicin for 77 days and in 6 of 6 guinea pigs given 160.0 mg/kg/day for the same period. Microscopic examination of cochleas from guinea pigs given gentamicin or kanamycin revealed extensive outer and inner hair cell loss in all animals. Cytocochleograms of 5 of 6 guinea pigs medicated with 160.0 mg/kg of hydroxygentamicin were comparable to those of the controls. In the sixth guinea pig there was a localized lesion involving all three rows of outer hair cells and some inner hair cells in the second turn. The results of this study indicated that hydroxygentamicin may be tolerated better than gentamicin in the guinea pig and therefore warrants further development as a new and less toxic aminoglycosidic antibiotic.

Spiral ganglion neuron loss following organ of Corti loss: a quantitative study

The packing density of spiral ganglion neurons was measured in 2.5- and 13-15-month-old guinea pigs, in guinea pigs at various times after drug-deafening or acoustic trauma, and in Waltzing guinea pigs of various ages. Analysis of variance and Duncan's new multiple range tests were used to determine significant differences between treatment/survival groups. Spiral ganglion neurons in young and old normal ears did not have significantly different packing densities. Drug-deaf guinea pigs showed a significant loss of neurons by 2 weeks following treatment, a further significant loss by 2 months, and a marginally significant loss between 4 and 8 months. The neuronal population was then stable through 15 months, at about 13% of normal. Acoustic trauma ears showed the first significant loss isn the lower second turn at 1 month. Long-term (12-14 months post-exposure) trauma ears were highly variable. Waltzers lost about 50% of their normal neuronal population between 4 and 8 months; they showed an unexpected greater-than-normal density at 2 months, possible explanations of which are discussed. Thus, loss of the organ of Corti from various causes results in a slow but progressive loss of spiral ganglion neurons, the time course of which varies with the type of cochlear insult.

The frequency selectivity of the normal and pathological human cochlea

Human AP tuning curves (tone on tone simultaneous and forward masking curves) were measured during transtympanic electrocochleography. For subjects with near normal thresholds, average Q10 dB values (simultaneous masking) were 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Patients with threshold elevations of more than 40 dB, resulting from sensorineural hearing loss of cochlear origin, had tuning curves less sharply tuned by a factor of 2-3, with Q10 dB values of 1-2 at 2 kHz and at 4 kHz, and 1-2.3 at 8 kHz. AP tuning curves and single fibre tuning curves (frequency threshold curves) were measured in normal guinea pigs; cochlear fibre tuning is sharper than AP tuning (simultaneous masking) by a factor of 1.8 (2-20 kHz). Assuming that this factor can be applied to the human cochlea, estimates of normal human cochlear fibre Q10 dB values are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz.

Are aminosugars ototoxic?

The ototoxicity of the kanamycin fragment 3-amino-3- deoxy-D-glucose (3-aminoglucose, kanosamine), was investigated by perilymphatic perfusion in the guinea pig. Concentrations of 10 or 28 mM of this compound had no effect on cochlear microphonic potentials (CM), contrasting with previous observations (Owada 1962). Kanamycin at 1 mM decreased CM significantly under otherwise identical conditions. The action of kanamycin was at least partially reversible.

Comparative ototoxicity of chloramphenicol and kanamycin with ethacrynic acid

Chloramphenicol is not ototoxic if administered for systemic effect, but topical applications of it to the middle ear produce severe cochlear toxic effects. Ethacrynic acid potentiates the ototoxicity of aminoglycosides. Guinea pigs were administered chloramphenicol or kanamycin sulfate with ethacrynic acid to compare the ototoxicity of chloramphenicol and ethacrynic acid with the ototoxicity of kanamycin and ethacrynic acid. Preyer's reflex audiometry and measurement of the endocochlear dc potential, the cochlear microphonics, and the negative potential of the organ of Corti indicate that ethacrynic acid does not potentiate the ototoxicity of chloramphenicol. There is not even indirect evidence that the blood-cochlear barrier for chloramphenicol is altered by ethacrynic acid. Assuming that the ototoxicity of chloramphenicol and ethacrynic acid are similar for man and guinea pig, the combination of the administration of chloramphenicol and ethacrynic acid of systemic effect in dosages commonly used clinically should not produce greater ototoxicity than either agent administered alone.

Increased ototoxicity in both young and old mice

Preweanling, postadolescent, and post-middle-aged CBA/J mice received injections of kanamycin sulfate for two weeks, followed by electrocochleographic (isoelectric auditory nerve-evoked potential thresholds from 2,000 to 64,000 Hz) and histocochleographic (hair cell counts from cochlea whole-mount preparations) analysis. The preweanling mice had structural and functional losses from all portions of the cochlea, while the postadolescent mice had no structural and minimal functional loss. The oldest mice had basal inner and outer hair cell loss and elevated high frequency thresholds. This is an experimental validation of the clinical observation that infants are most susceptible to aminoglycosidic ototoxicity. It also support the suspicion that older persons are also susceptible to ototoxicity and provides the first animal model for experimentally investigating these age-dependent effects.

Ultrastructural correlates of selective outer hair cell destruction following kanamycin intoxication in the chinchilla

Kanamycin ototoxicity, combined with behavioral audiometry to evaluate threshold shifts, was used to destroy outer hair cells (OHCs) in the basal cochlea of the chincilla while leaving the inner hair cell (IHC) population largely intact. After survival times of four weeks to one year, transmission electron microscopy was employed to determine the condition of surviving hair cells and neural elements. Throughout the region of OHC loss, IHCs and their innervation were normal in appearance if their adjacent supporting cells were undamaged. When IHC supporting cells, specifically the inner pillar cells, were damaged or absent, damage to IHCs was commonly observed. Such supporting cell-related damage included extrusion of the cuticular plate from the surface of the reticular lamina, encapsulation and/or fusion of stereocilia, and gross distortion of hair cell shape. When the outer supporting cells of the organ of Corti were undamaged following OHC loss, outer spiral fibers were found to have survived in near-normal numbers in the region from 0.5-1.0 mm basal to the basal most surviving OHC, but suffered progressive attrition toward the basal end of the cochlea. It is concluded that kanamycin-induced OHC loss can occur without concommitant IHC damage or outer spiral fiber loss.

Combined effects of noise and kanamycin. Cochlear pathology and pharmacology

Concurrent administration of aminoglycoside antibiotics and acoustic exposure is reported to result in a cochlear damage level exceeding that predicted from the effects of either agent given alone. To investigate this interaction, guinea pigs were given daily subcutaneous injections of kanamycin sulfate at 200, 300, or 400 mg/kg followed by a ten-hour noise exposure (115 or 45 dB) for seven consecutive days. Drug levels in plasma and perilymph were measured during the 24 hours after injection and during the seven-day period of drug and noise exposures. Electrophysiological and morphological evaluation of cochlear function confirmed a dramatic interaction at the 300-mg/kg dosage. Augmentation of damage was minimal at 200 mg/kg and masked by ceiling effects at 400 mg/kg. No alteration in accumulation or elimination of kanamycin occurred as a result of high-intensity acoustic exposure.

Histological evaluation of ototoxic reaction due to some aminoglycoside antibiotics

Twenty-one days s.c. treatment with netilmicin, gentamicin, sisomicin, and kanamicin at different doses were performed in albino guinea pigs of both sexes. Block surface preparation of Corti's organ was carried out and missing OHCs and IHCs counted in selected areas of each turn. The animals treated with gentamicin and sisomicin showed a dose-depending missing of hair cells, preferably relative to the outer ones and quantitatively the same for both the antibiotics. Furthermore, a characteristic distribution of the damage progressively increasing from the apex to the basal turn of the cochlea was detected. Kanamicin at 267 and 400 mg/kg gave the complete destruction of OHCs and IHCs along the whole cochlea while at 178 mg/kg did not show any significant damage in comparison to the control group. Finally, netilmicin neither damaged Corti's organ nor statistically determined missing OHCs and IHCs at all the doses used. These histological results and the previous electrophysiological and reflexological observations obtained in the guinea pig show a higher safety of netilmicin in comparison to the other aminoglycosides used for the problem relative to ototoxicity.

Acoustic priming and kanamycin-induced chochlear damage

The cochleae from 3 lines of mice, selectively bred for differential susceptibility to priming-induced audiogenic seizures, were examined following acoustic priming and retest or kanamycin treatment, and the degree of cochlear damage was assessed. After 60 sec of acoustic priming, animals from the high and unselected lines which had subsequently developed audiogenic seizure susceptibility exhibited severe cochlear damage limited to the outer hair cells. Low line mice, which had been selected for resistance to acoustic priming-induced audiogenic seizures and were not seizure susceptible, exhibited no cochlear pathology following acoustic priming. Following kanamycin treatment, all 3 lines developed subsequent audiogenic seizure susceptibility. Histological examination of cochleae from mice so treated revealed a pattern of damage similar to that caused by acoustic priming, except that the cochleae of priming-induced audiogenic seizure resistant low line mice revealed a significant amount of outer hair cell damage. The results are discussed with respect to the physiological mechanism underlying a selectively bred behavioral phenotype in terms of a possible instance of damage/disuse-supersensitivity in the central nervous system.

Ototoxicity of kanamycin in developing rats: relationship with the onset of the auditory function

In order to test the relationship between the ototoxicity of kanamycin and the onset of the auditory function, two groups of developing rats were intoxicated with kanamycin before and after the period of onset of cochlear potentials (8th postnatal day). Kanamycin was shown to have a weak ototoxic effect before the 8th postnatal day and a strong ototoxic effect after this period. These results indicate a critical period of sensitivity to ototoxic antibiotics during auditory development.

Effects of noise on cochlear potentials and endolymph potassium concentration recorded with potassium-selective electrodes

Guinea pig cochleas were exposed to either broad-band noise at intensities between 95 and 115 dBA or octave-band noise centered at 380 Hz or 4.2 kHz at intensities between 115 and 125 dB SPL. Cochlear microphonics (CM), summating potentials (SP) and action potentials (AP) were recorded from differential electrodes in the perilymphatic scalae between successive 20-min periods of noise exposure. The endocochlear potential (EP) and endolymph potassium concentration [Kendo+] were recorded continuously from scala media using double-barreled potassium-sensitive electrodes. It was found that the initial exposure to noise at 115 dBA produced considerable suppression of the CM and AP, while the EP and [Kendo+] were elevated above their normal values. When animals previously treated with kanamycin were subjected to the same level of noise exposure no systematic increase in either EP ro [Kendo+] was observed. After prolonged exposure to 380 Hz octave-band noise at 125 dB SPL, a slow decline of EP and [Kendo+] was observed. The relationships between the changes in EP, [Kendo+] and CM are discussed.

[Dependence of the nephrotoxic effect of kanamycin on its concentration in the blood (an experimental study)]

The kinetics of changes in the urea nitrogen level of the serum was studied experimentally on narcotized cats with constant blood levels of kanamycin. A relationship between the intensity of the nephrotoxic effect of kanamycin and its blood level was found. On the basis of this relationship lower nephrotoxicity of kanamycin as compared to that of gentamicin and streptomycin under conditions of their constant blood levels was shown. However, the concentrations of gentamicin and kanamycin provided in the blood by their use in therapeutic doses differeing 3--4 times allow a conclusion that the nephrotoxic effect of kanamycin and gentamicin to be practically the same.

The effect of topical application of antibiotics on the cerebral cortex: an experimental update

✓ A common complication of intrathecal sepsis is the development of clinical seizure activity. However, some of the newer, commonly used antibiotics may have epileptogenic and electrocortical depressant effects when applied topically to the cerebral cortex. Epileptogenic characteristics of these antibiotics may be masked by the known tendency for intracranial sepsis to produce both early and late clinical seizure problems. In this experimental study, electrocortical spike activity was produced by penicillin, methicillin, cephalothin, carbenicillin, colistimethate, and neomycin, and electrocortical depression was caused by tobramycin and gentamicin. A mixed picture was found with neomycin and carbenicillin.

Quantitative relationships of the ototoxic interaction of kanamycin and ethacrynic acid

We determined the range of doses of kanamycin sulfate and ethacrynic acid that results in an ototoxic interaction in guinea pigs. In addition, we determined the time interval between the administration of the two drugs that is needed to produce this interaction. In all cases, the magnitude of the ototoxic lesion was determined by measuring the cochlea's ability to generate both the sensitivity and intensity functions of the ac cochlear potential. In addition, the cochlear pathologic conditions, as determined by counting the number of missing hair cells in the organ of Corti, was found to correlate highly with the ac cochlear potential data. The dosage range of ethacrynic acid during which the interaction occurs is very narrow, while the dose range of kanamycin is very large.

Interaction of kanamycin and noise exposure

The amount of hair cell damage in the cochleas of guinea pigs after exposure to different experimental conditions suggests that a 'safe' level of kanamycin has a potentiating effect on damage due to noise. Such an effect lasts more than 20 days after the cessation of the drug administration.

Critical bands following the selective destruction of cochlear inner and outer hair cells

Critical bandwidths and absolute intensity thresholds were measured in cats before and after kanamycin treatment which induced selective inner and outer hair cell losses. Hair cell losses were measured from cochleograms constructed from surface preparations of the organ of Corti. Results suggested that, for the test frequencies and stimulus intensities employed, critical bandwidths were not affected for frequencies tonotopically located in cochlear regions where only outer hair cells were lost. Critical bands were widened or not measurable only when inner hair cell losses exceeding 40% were also associated with complete loss of outer hair cells. The experiment suggests that cochlear frequency selectivity can be mediated by inner hair cells alone.

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.

Effects of kanamycin on the auditory evoked responses during postnatal development of the hearing of the rat

The ototoxic effects of kanamycin were studied in rats during the early postnatal period and at an adult age. Brain stem potentials as well as auditory cortical potentials were used for the estimating of ototoxic damage. The auditory potentials decreased promptly and markedly in the animals which were treated daily with 400 mg/kg body weight of kanamycin starting from the 11th day after birth. In these animals, the auditory potentials were almost completely abolished within 10 days after the beginning of the kanamycin treatment. However, when the same amount of kanamycin was applied earlier or later than that, i.e., avoiding the period of the initial appearance and the greatest development of auditory functions (from the 11th to the 15th day after birth in the rat), the auditory potentials were not apparently damaged. In light and scanning electronmicroscopy, marked ototoxic changes were observed which underlay the functional damage. The meaning of these findings is discussed.

Ototoxic effects of the interaction between kanamycin and ethacrynic acid. Cochlear ultrastructure 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.

Behavioral ototoxicology

Methods for the evaluation in experimental animals of toxic substances that produce hearing impairment are described. In the experiments reported here, animals were trained by positive reinforcement operant conditioning procedures so that their hearing could be examined by behavioral means. When normal hearing was established, aminoglycosidic antibiotics (kanamycin and dihydrostreptomycin) were given daily and hearing tests administered in order that the course of hearing loss could be closely followed. Initial loss of sensitivity to the high frequencies always progressed in time to impairment at the low frequencies, and these changes in hearing were correlated with a loss of receptor cells in the inner ear which started in the basal region of the cochlea and advanced toward the apex. Although such behavioral procedures are moderately expensive to instrument and relatively time-consuming to apply, they are shown to yield valid quantitative measures of hearing. Further, they provide for reliable early detection of the toxic process and a measure of behavioral impairment that can be precisely related to the histopathological changes that occur simultaneously in the inner ear and auditory nerve.

A possible involvement of acidic glycosaminoglycans in kanamycin ototoxicity

The content of acidic glycosaminoglycans (AGAG) was determined quantitatively by electrophoretic microanalysis in the cochlea, kidney and brain of the guinea pig. Kanamycin treatment (400 mg/kg body weight/day, i.m., 10 successive days) reduced the content of AGAG markedly in the lateral wall of the membranous cochlea. Furthermore, from the results of the ultrahistochemical and freeze-fracturing study, we propose here an "excretion system for basic aminoglycoside antibiotics" by means of the co-operation of spiral ligament cells and AGAG produced by them. Thus we have tentatively concluded both that kanamycin is excreted via the above mentioned "excretion system" in the lateral wall of the membranous cochlea and that it damages this system to form the circulus vitiosus of its opopoxicity.

Tissue levels of kanamycin in correlation with oto- and nephrotoxicity

The time courses of kanamycin (KM) levels in the perilymph, kidney, liver, brain and blood were observed by a bioassay method in normal guinea pigs and in animals pretreated with KM for 10 successive days. In the kidney and perilymph of the normal guinea pigs, the injected KM became highly concentrated and was eliminated only after a protracted delay. This tendency was much more intensified in kidney and perilymph of the pretreated animals. By contrast, the KM in blood and brain was eliminated rapidly both in the normal and in the pretreated animals. It is concluded that the high accumulation and slow elimination of KM by the inner ear and kidney and, moreover, the enhancement of these phenomena by successive pretreatment are one of the important factors in the origin of oto- and nephrotoxicity.

Potentiation and its mechanism of cochlear damage resulting from furosemide and aminoglycoside antibiotics

The severe ototoxic interaction of the combined administration of furosemide and aminoglycoside antibiotics (kanamycin, streptomycin and gentamicin) was studied in rabbits, and its mechanism clarified. Severe damage occurred not only in the inner ear but also in the kidney when both furosemide and aminoglycoside antibiotics were administered to rabbits. Kanamycin concentration after a single injection of kanamycin with furosemide was much higher not only in the perilymph but also in the cerebrospinal fluid and serum than that after a single injection of kanamycin alone. The ototoxic interaction following the combined use of furosemide and aminoglycoside antibiotics seems to be caused mainly by the inhibitory effect of furosemide on the excretion of aminoglycoside antibiotics from the kidneys.

Quantitative analysis of kanamycin ototoxicosis

The morphological changes after kanamycin intoxication of the inner ear, including both the cochlea and the vestibule, were quantitatively analysed by the surface preparation technique after succinic dehydrogenase staining. 75 guinea pigs were used. The outer hair cells in the basal coil and the inner hair cells in the upper coils of the cochlea were the most severely damaged, but many unusual modes of damage were also revealed. For example, the initial hair cell damage in the cochlea appeared in the upper hair cells. The clearly observed vestibular damage contradicts the general belief that kanamycin is not so toxic to the vestibular hair cells. The utricular macula and the lateral crista were most severely damaged. The delayed ototoxicity of kanamycin was observed for the first time in the vestibular hair cells.

Ototoxicity and the olivocochlear bundle

Cochlear hair cell damage due to kanamycin sulfate was studied in chinchillas receiving 200 mg/kg kanamycin for nine days. The drug was given to a group of animals with lesions of the crossed olivocochlear bundle, a group that had received a sham operative procedure, and a group of normal animals. The animals were sacrificed 14 days after the last drug injection and the cochleae removed for examination by surface preparation. The lesioned animals showed markedly less hair cell loss than the control groups, and this was attributed to the fact that the loss of the efferent endings rendered these animals less susceptible to the ototoxic effects of kanamycin.

Toxicity of aminoglycoside antibiotics

In cats, aminoclycosides cause vestibular damage followed in a few days by renal damage. The reverse is true in the dog, except that streptomycin causes vestibular damage prior to renal damage. To avoid toxicities, therapeutic doses of aminoglycosides should not be given longer than a week and they should be given cautiously in animals with renal impairment. Failure of the kidneys to eliminate aminoglycosides will result in very high blood levels, even with therapeutic doses, that can cause further renal and vestibular damage. The oral administration of aminoglycosides is seldom dangerous when normal therapeutic doses are employed. Although it is remote, the possibility exists that animals with renal impairment and intestinal obstruction may become intoxicated. Kanamycin is less nephrotoxic to dogs than neomycin and it is less destructive to the auditory nerve than vestibular damage than streptomycin. Gentamicin in cats is twice as toxic to the vestibular apparatus as streptomycin and more toxic to the cochlea than streptomycin or dihydrostreptomycin. Neomycin is more toxic than kanamycin, gentamicin, and streptomycin to both cats and dogs. Amikacin causes renal damage in dogs similar to other aminoglycosides. It also causes vestibular damage.

A new aminoglycoside antibiotic complex--the seldomycins. I. Taxonomy, fermentation and antibacterial properties

A soil isolate named Streptomyces hofunensis sp. nov. was found to produce seldomycin factors 1, 2, 3 and 5, new aminoglycoside antibiotics. Taxonomy of the producing organism, a study of cultural conditions for seldomycin production, and antibacterial activity of seldomycins are reported. Seldomycin factor 5 was the most active both in vitro and in vivo against gram-positive and negative bacteria.

[Side effects of aminoglycosides: nephrotoxicity (author's transl)]

Animal experiments showed that all aminoglycosides cause similar toxic tubular and glomerular damage when investigated by qualitative morphology. Quantitative differences in the tubular nephrotoxicity of gentamicin, tobramycin, sisomicin, kanamycin, kanendomycin, amikacin, and butirosin can be demonstrated experimentally by evaluation of the excretion rates of tubular cells and urinary enzymes in rats. By this means dose-effect relationships were established resulting in varying reproduceable toxic threshold doses for each antibiotic, and thus in a scale of increasing nephrotoxicity. The aminoglycosides differed in their affinity to kidney tissue as measured by determination of the accumulating renal concentrations of the drugs at different times during multiple-dose administration. This had a modifying influence on excretion rates of cells and enzymes affecting the scale of toxicity in long-term studies. Comparative investigations on nephrotoxicity in rats and guinea pigs gave similar results. In addition, a study in man suggested that the test results of nephrotoxicity are not species-specific. For human therapy it is concluded that even more caution should be practised with the new aminoglycerides than with gentamicin in order to avoid renal damage.

Further studies on effects of irrigation solutions on rat bladders

Further studies on the effects of certain irrigating fluids on the rat bladder for 18 hours are reported. The results have shown that the degradation product p-choloroaniline is not a significant factor in chlorhexidine-digluconate associated erosive cystitis. A high percentage of kanamycin-colistin and povidone-iodine irrigations were associated with erosive cystitis and suggested a possible complication with human usage. Picloxydine irrigations appeared to have a lower incidence of erosive cystitis but further studies would have to be performed before it could be recommended for use in urological procedures.

The influence of pigmentation of rats and guinea-pigs on the ototoxicity of kanamycin and neomycin

Following the finding that melanin pigment played a role in the accumulation of ototoxic drugs in the inner ear, an investigation was made of the possible influence of the pigmentation of animals on their susceptibility to the ototoxic effects of drugs. Hearing acuity was assessed by measurement of acoustic startle reaction. Preliminary experiments suggested that pigmented animals might be more likely to suffer hearing impairment following ototoxic drug administration. However, in a controlled study using rats treated with kanamycin, it was not possible to confirm this and albino animals appeared no less vulnerable than pigmented animals to kanamycin-induced deafness.