Comparative cochlear toxicities of streptomycin, gentamicin, amikacin and netilmicin in guinea-pigs

Coordination Chemistry, Antibacterial Screening, and In Silico ADME Study of Mononuclear NiII and CuII Complexes of Asymmetric Schiff Base of Streptomycin and Aniline

Two novel metal complexes, that is, Ni (StmAn)2(4) and Cu (StmAn)2(5), were synthesized from unsymmetrical Schiff base ligand StmAn (3). The ligand was prepared by refluxing streptomycin (2) and aniline (1). They were characterized by elemental microanalysis, conductivity measurements, and spectroscopic techniques such as 1H NMR, FT-IR, ESI-mass, and electronic absorption spectral study. Interestingly, the study revealed metal coordination through azomethine nitrogen and N-atom of NH-CH3 of N-methyl-L-glucosamine unit of streptomycin. The electronic absorption spectral study supported an octahedral geometry for complex 4 and a tetrahedral geometry for complex 5. Particle size calculation by Scherrer’s formula indicated their nanocrystalline nature. The geometry optimization of the complexes was achieved by running an MM2 job in Gaussian supported Cs-ChemOffice ultra-12.0.1 and ArgusLab 4.0.1 version software. Based on SwissADME predictions, a theoretical drug profile was generated by analyzing absorption, distribution, metabolism, excretion, and toxicity (ADMET) scores of the compounds. They were screened for in vitro antibacterial activity study against four clinical pathogens such as E. coli, S. pneumoniae, P. vulgaris, and S. aureus. Minimum inhibitory concentration (MIC) study demonstrated greater inhibitory potency of complex (4) (0.024 g/L) for S. aureus relative to ligand (3) and complex (5). Studies show that metal complexes are more toxic to bacteria.

Effect of Dexamethasone Combination with Gentamicin in Chemical Labyrinthectomy on Hearing Preservation and Vertigo Control in Patients with Unilateral Meniere's Disease: A Randomized Controlled Clinical Trial

Chemical labyrinthectomy using gentamicin is a popular method for treating intractable vertigo attacks in Meniere’s disease. However, the risk of hearing loss remains a major concern for clinicians. We investigated the effect of simultaneous dexamethasone and gentamicin application on hearing preservation and vertigo control in patients with intractable unilateral Meniere’s disease. A single-institutional, prospective, single-blinded, randomized clinical trial was conducted. Gentamicin-soaked Gelfoam^® was directly applied on the oval window following middle ear exploration. On the round window, dexamethasone-soaked Gelfoam^® was applied in the gentamicin with dexamethasone group (GD group, n = 18), and saline-soaked Gelfoam^® was applied in the gentamicin with sham reagent group (GO group, n = 19). The hearing change 8 weeks after the procedure and vertigo control 2–12 months after the procedure were investigated. The high-frequency hearing threshold was significantly increased in the GO group (p = 0.005 and 0.012 for 4 and 8 kHz, respectively), but not in the GD group. The short-term (2–6 months) vertigo control was more successful in the GD group (57.89% vs. 94.44%, p = 0.019), but long-term control (6–12 months) was insignificant. In conclusion, the combined application of gentamicin and dexamethasone in chemical labyrinthectomy is an effective method for protecting high-frequency hearing and vertigo control.

Acanthamoeba keratitis in Mexico: Report of a clinical case and importance of sensitivity assays for a better outcome

Acanthamoeba keratitis (AK) is a sight-threatening corneal infection. The early symptoms include redness, pain, photophobia and intense tearing. Chronic infection usually progresses to stromal inflammation, ring ulcers, corneal opacification and hypopyon. Here we document an AK case in a high myopic 38-year-old woman from Mexico City, with a history of wearing contact lenses while swimming. Corneal scrapes cultures were positive only for amoebae, consequently a treatment including netilmicin 0.3% and oral itraconazole 100 mg/12 h was prescribed. The infection was resolved after 8 months, leaving a slight leucoma outside the visual axis, with a visual acuity of 20/150. In the laboratory, the amoebic isolate was axenized in PYG medium, with an optimal growth at 30 °C, and was identified morphologically as Acanthamoeba polyphaga according to the taxonomic criteria of Page (1988) and placed in the T4 group by genotyping. The virulence of this strain (40%) was determined by intranasal inoculation of 1 × 10⁶/20 μl trophozoites in BALB/c mice recovering from brain, proving their invasion ability and by the interaction with monolayers of epithelial cells of the established MDCK line of canine kidney origin (1:2 ratio of interaction), at 1, 3, 6, 8 and 24 h; trophozoites migrated to cell junctions inducing few lytic zones. In addition to the biological characterization, in vitro drug sensitivity tests were performed using chlorhexidine, itraconazole, netilmicin and voriconazole. Results revealed that voriconazole was the most effective compound. A. polyphaga remains as one of the most frequently isolated species producing AK. The treatment of AK case using netilmicin and oral itraconazole solved the disease, but the healing process was wide-ranging (8 months). The use of voriconazole and chlorhexidine may be an alternative treatment of future AK cases in Mexico.

The Effect of Radiotherapy on Gentamicin Ototoxicity

Objective

Patients undergoing radiotherapy (RT) often present with serious bacterial infections requiring the use of antibiotic treatment. Gentamicin is a commonly used aminoglycoside antibiotic, whose ototoxicity remains a major problem in clinical use. The objective of this study was to determine whether radiation exposure can influence gentamicin-induced ototoxicity.

Study Design

Prospective animal study.

Setting

Animal care facilities of the Montreal Children’s Hospital Research Institute.

Methods

Sixteen guinea pigs received low-dose RT unilaterally for 4 weeks (total: 48 Gy). Animals then received low or high doses of gentamicin (40 mg/kg/d and 80 mg/kg/d) for 10 days. The ears were divided into 4 groups: gentamicin 40 mg, gentamicin 80 mg, gentamicin 40 mg + RT, and gentamicin 80 + RT. Auditory brainstem responses and distortion products otoacoustic emissions were assessed at baseline and before and after gentamicin treatment. Cochlear morphology using light and scanning electron microscopy were evaluated.

Results

High-dose gentamicin caused significant auditory brainstem response threshold shifts ( P = .020), with greater hearing loss in the irradiated ear (difference of 23.6 + 7.5 dB). All animals exposed to high-dose gentamicin had head tilts toward the radiated side. Cochlear morphology revealed the greatest hair cell damage in the gentamicin 80 + RT group followed by gentamicin 80.

Conclusion

Results suggest that radiation can exacerbate the ototoxicity of gentamicin at high doses.

Ototoxic effect of daptomycin applied to the guinea pig middle ear

CONCLUSION

Daptomycin applied topically at a concentration of 50 mg/ml caused mild but statistically significant hearing impairment. Outer hair cells were not damaged by daptomycin. Great care must be taken when there is a chance that daptomycin can reach the middle ear.

OBJECTIVE

Ototopic antibiotic eardrops are frequently used to treat external and middle ear infections. Daptomycin is a new anti-methicillin-resistant Staphylococccus aureus (MRSA) drug with unknown ototoxicity. The current study examined the ototoxic effect of daptomycin in topical applications to guinea pig ears.

METHODS

Twenty-three male Hartley guinea pigs (weight, 250-640 g) were divided into three groups receiving daptomycin (50 mg/ml), gentamicin (50 mg/ml, positive control), or saline solution (negative control). After insertion of a pressure-equalizing tube, pretreatment auditory brainstem responses (ABRs) were obtained. Topical solutions of 0.1 ml were applied through the tube into the middle ear twice a day for 7 days. Post-treatment ABRs were obtained 7 days after the last treatment. Hair cell loss was investigated with whole-mount cochlear surface preparations.

RESULTS

The saline-treated (negative control) group showed no deterioration of ABR threshold. The daptomycin-treated group showed mild deterioration and the gentamicin-treated group showed severe deterioration in ABR threshold. Hair cells were preserved in the daptomycin- and saline-treated groups but severely damaged in the gentamicin group.

Transient ischemia/hypoxia enhances gentamicin ototoxicity via caspase-dependent cell death pathway

Aminoglycoside ototoxicity is a common cause of drug-induced hearing loss. Toxicity is dose related, but some patients may still develop hearing loss even under safe dosage. Apart for genetic idiosyncrasy, indirect evidences imply that ischemia may increase the aminoglycoside ototoxic sensitivity because common clinical situations associated with cochlear ischemia such as noise, sepsis, and shock are known to augment the development of aminoglycoside ototoxicity. At present, a direct interaction of cochlear ischemia and aminoglycoside ototoxicity is still lacking. This study demonstrated a direct evidence of increased gentamicin (GM) ototoxic sensitivity in chronic guinea pig models of transient cochlear ischemia. No permanent auditory changes were observed after a single dose of GM (125 mg/kg) or after transient cochlear ischemia for 30 min. Persistent and significant auditory threshold shift was detected when GM was given after transient cochlear ischemia. Cochlear hair cells and spiral ganglion neurons are the major regions affected. Apoptosis contributes to hair cell death during acute interaction of ischemia and GM ototoxicity. Increased apoptotic cell death was also depicted when GM crossreacted with hypoxia in vitro, using cochlear cell lines. Generation of reactive oxygen species, loss of mitochondrial membrane potential, calcium release, and caspase-dependent apoptotic cell death were shown during the interaction of hypoxia and GM ototoxicity in vitro. This synergistic ototoxicity may be critical to aminoglycoside-induced hearing loss in clinical scenarios. The results should improve our understanding of the interacting mechanism and potential preventive strategy to aminoglycoside ototoxicity.

Protective effect of melatonin against gentamicin ototoxicity

Objective:

To research the protective effect of melatonin against gentamicin ototoxicity.

Methods:

Guinea pigs were randomly divided into four groups. The first group received intramuscular gentamicin (120 mg/kg body weight/day) for 17 days. Over the same time period, a second group simultaneously received intramuscular gentamicin (120 mg/kg body weight/day) plus (on the other side) intramuscular melatonin (0.3 ml kg body weight/day). Two groups of controls were treated for 17 days with either intramuscular melatonin or intramuscular saline. After the 17 days, each animal underwent distortion product otoacoustic emission testing (both ears). The guinea pigs were sacrificed by decapitation just after the final injection. Their cochleae were used to produce a tissue section, surface preparation and scanning electron microscope preparation.

Results:

Distortion product otoacoustic emission testing indicated gentamicin-induced hearing loss at 3, 4, 6 and 8 kHz in gentamicin-treated animals. Animals receiving melatonin co-therapy had significantly attenuated hearing loss and their cochleae showed lower rates of outer hair cell loss (comparing the same cochlear turns), compared with gentamicin-treated animals (p < 0.01).

Conclusion:

These findings confirm the occurrence of outer hair cell loss after gentamicin treatment, and the attenuation of such loss following simultaneous melatonin injection, using the method of morphological evaluation. These results suggest that melatonin protects against gentamicin ototoxicity by interfering with cytotoxic mechanisms.

Effects of Piracetam Supplementation on Cochlear Damage Occuring in Guinea Pigs Exposed to Irradiation

In this study we aimed to determine the role of piracetam (PIR) in preventing radiation induced cochlear damage after total-cranium irradiation (radiotherapy; RT). Male albino guinea pigs used in the study were randomly divided into three groups. Group 1 (Control group) (n=11) received neither PIR nor irradiation, but received saline solution intraperitoneally (i.p.) and received sham irradiation. Group 2 (RT group) (n=32) was exposed to total cranium irradiation of 33 Gy in 5 fractions of 6.6 Gy/d for five successive days, with a calculated (alpha/beta=3.5) biological effective dose of fractionated irradiation equal to 60 Gy conventional fractionation, then received saline solution for five successive days i.p. Group 3 (PIR+RT group) (n=33) received total cranium irradiation, plus 350 mg/kg per day PIR for five successive days i.p. After the last dose of RT, the guinea pigs were all sacrificed at the 4th, 24th and 96th hours, respectively. Their cochleas were enucleated for histopathologic examination. It was observed that total cranium irradiation (RT group) promoted degeneration in stria vascularis (SV), spiral ganglion cells (SG), outer hair cells (OHC) and inner hair cell (IHC) of cochleas at these times (p<0.05). While in the PIR+RT group, there was no statistically significant difference on radiation-induced cochlear degeneration in SV and OHC at 4th (p>0.05) and IHC at 4th, 24th hours (p>0.05), there was a significant difference on radiation-induced cochlear degeneration in SV and OHC at 24th and 96th hours (p<0.05), IHC at 96th hour (p<0.05) and SG at 4th, 24th and 96th hours (p<0.05). There was no any cochlear degeneration in the control group. Piracetam might reduce radiation-induced cochlear damage in the guinea pig. These results are pioneer to studies that will be performed with PIR for radiation toxicity protection.