Postauricular hypodermic injection to treat inner ear disorders: experimental feasibility study using magnetic resonance imaging and pharmacokinetic comparison

Ototoxic effects of unilateral postauricular neomycin administration on the inner ears of Guinea pigs

BACKGROUNDS

Due to the therapeutic needs of inner ear diseases, a simple method of inner ear drug delivery has been under exploration. Postauricular administration, which involves injecting the drug through the middle of the retroauricular groove, is a potential novel approach, but its mechanisms remain unclear.

OBJECTIVES

To investigate threshold shifts in the auditory brainstem response (ABR), as well as the morphology and quantity of hair cells on the bilateral inner ear of guinea pigs after postauricular neomycin administration.

MATERIAL AND METHODS

Thirty healthy guinea pigs were divided randomly into two groups and administered either neomycin 200 mg/kg or saline 1 ml via daily postauricular injection for 10 days. Auditory threshold-shifts were examined by tests of the ABR. The quantity and morphology of hair cells in the organ of Corti were assessed by confocal laser scanning microscopy.

RESULTS

The ABR results showed that at a frequency of 16 kHz, the threshold shift was 21.00 ± 14.49 dB in the neomycin injection side, 10.00 ± 16.67 dB in the contralateral side, and 0.50 ± 3.69 dB in the saline group. At a frequency of 24 kHz, the threshold shift was 37.00 ± 16.36 dB in the neomycin injection side, 14.50 ± 9.26 dB in the contralateral side, and 1.00 ± 2.11 dB in the saline group. Histopathological analysis revealed that the outer hair cells (OHCs) in the neomycin injection side suffered significant morphological and numerical loss, while the OHC loss in the contralateral ear was less severe than in the injection side but greater than in the saline group.

CONCLUSIONS AND SIGNIFICANCE

This study confirms that postauricular administration is a novel method of local drug delivery to the inner ear, which has practical value in future experimental modeling and the treatment of inner ear diseases.

Clinical characteristics of sudden hearing loss during pregnancy

Objective

The objective of this study was to explore the clinical characteristics and management of sudden hearing loss (HL) during pregnancy, thus better guiding the clinical practice.

Methods

The clinical and follow-up data of 17 patients (17 ears) with sudden HL during pregnancy were analyzed retrospectively (the observe group). Twelve nonpregnant female patients (12 ears) with sudden HL of similar clinical characteristics were selected as the control group. The prognosis of the two groups was compared. All the patients were followed up after delivery, and two of them were readmitted to the hospital 1-2 months after delivery.

Results

The observe group had better improvement in hearing and a higher response rate compared to the control group. The pure tone hearing and speech recognition rate of patients could still be improved after the readmitted treatment, and the hearing could partially recover spontaneously during follow-up. The laboratory indicators that affect the inflammatory response and coagulation pathway were significantly different between the two groups.

Conclusions

The hearing condition of sudden HL during pregnancy is severe, and the prognosis of these patients is better than nonpregnant patients of similar clinical characteristics. Postpartum treatment is still effective, and some patients showed self-healing with time during follow-up. The inflammatory response and coagulation function may affect the hearing of patients through a metabolic pathway.

The auditory function in migraine model rats induced by postauricular nitroglycerin injection

Objective

The mechanism by which migraines produce inner ear-related symptoms is not well understood. Previous studies have found that the latency of auditory brainstem response (ABR) in animal models of migraine has changed, but the threshold has not changed significantly. Therefore, it is necessary to establish a better animal model with both migraine and hearing loss to explore the relationship between migraine and auditory function deeply.

Methods

In this study, the rat model of migraine was induced by postauricular injection of nitroglycerin (NTG), and the effect on the auditory function of the inner ear was explored by comparing with intraperitoneal injection of nitroglycerin. The rats were given the drug repeatedly on alternate days, a total of 5 dosing, with the body weight monitored during the drug administration. The tactile threshold of the rats' forepaw was measured using von-Frey filaments and auditory function was assessed by ABR.

Results

The results showed that the baseline tactile threshold of rats gradually decreased during the modeling process, and hyperalgesia appeared. Postauricular injection of NTG did not affect the weight gain of rats, while intraperitoneal injection of NTG showed slow or even negative weight gain. The ABR threshold of Click, 4 and 8 kHz of postauricular NTG injection rats increased, the latency was prolonged, and the ABR threshold in the right ear was higher than that in the left ear.

Conclusions

We demonstrated that postauricular injection of nitroglycerin may be safer and more effective than intraperitoneal injection of nitroglycerin in the process of creating rat migraine model without affecting the weight gain. Postauricular injection of nitroglycerin has more damage to the auditory function of rats. Therefore, the migraine model rat induced by postauricular injection of nitroglycerin may be a new model of cochlear migraine.

Serum/glucocorticoid-inducible kinase 1 deficiency induces NLRP3 inflammasome activation and autoinflammation of macrophages in a murine endolymphatic hydrops model

Ménière's disease, a multifactorial disorder of the inner ear, is characterized by severe vertigo episodes and hearing loss. Although the role of immune responses in Ménière's disease has been proposed, the precise mechanisms remain undefined. Here, we show that downregulation of serum/glucocorticoid-inducible kinase 1 is associated with activation of NLRP3 inflammasome in vestibular-resident macrophage-like cells from Ménière's disease patients. Serum/glucocorticoid-inducible kinase 1 depletion markedly enhances IL-1β production which leads to the damage of inner ear hair cells and vestibular nerve. Mechanistically, serum/glucocorticoid-inducible kinase 1 binds to the PYD domain of NLRP3 and phosphorylates it at Serine 5, thereby interfering inflammasome assembly. Sgk^-/- mice show aggravated audiovestibular symptoms and enhanced inflammasome activation in lipopolysaccharide-induced endolymphatic hydrops model, which is ameliorated by blocking NLRP3. Pharmacological inhibition of serum/glucocorticoid-inducible kinase 1 increases the disease severity in vivo. Our studies demonstrate that serum/glucocorticoid-inducible kinase 1 functions as a physiologic inhibitor of NLRP3 inflammasome activation and maintains inner ear immune homeostasis, reciprocally participating in models of Ménière's disease pathogenesis.

Diagnosis, differential diagnosis, and treatment for sudden sensorineural hearing loss: Current otolaryngology practices in China

Introduction

Although sudden sensorineural hearing loss (SSNHL) has been attempted to be understood for 70 years, diagnosis and treatment strategies still have strong heterogeneity worldwide, which are reflected in the guidelines issued by countries and the clinical practice of otolaryngologists.

Methods

Questionnaires were sent to registered otolaryngologists nationwide via an online questionnaire system. We investigated the current views and clinical practices of otolaryngologists in mainland China about the diagnosis, examination, and treatment strategies of SSNHL.

Results

Most otolaryngologists supported diagnostic classification via audiograms. Regional economic situation and hospital grade affected application strategies for differential diagnosis. Regarding corticosteroid therapy, 54.9% of respondents opted to discontinue the drug 5 days after systemic administration. Both intratympanic therapy and post-auricular injections were selected by more than half of the respondents as initial and salvage treatments.

Discussion

Chinese otolaryngologists exhibit heterogeneity in clinical practices for SSNHL, including distinct approaches to combination therapy and local application of steroids. This study pointed out Chinese doctors' similarities, differences, and unique strategies in diagnosing and treating SSNHL and analyzed the possible reasons to help the world understand the current otolaryngology practices in China.

Efficacy of intratympanic or postauricular subperiosteal corticosteroid injection combined with systemic corticosteroid in the treatment of sudden sensorineural hearing loss: A prospective randomized study

Objectives

This study aimed to investigate the efficacy and safety of intratympanic or postauricular subperiosteal glucocorticoid injection combined with systemic glucocorticoid in the treatment of sudden sensorineural hearing loss (SSNHL).

Methods

This study is a prospective randomized controlled study. This study included unilateral SSNHL patients who were hospitalized in our department between January 2020 and June 2021. Patients were randomly divided into three groups (groups A, B, and C). Patients in group A were treated with an intratympanic corticosteroid injection combined with systemic corticosteroid treatment, and patients in group B received a postauricular corticosteroid injection combined with systemic corticosteroid treatment. Patients in group C (control group) were treated with systemic corticosteroid alone. The case number of groups A, B, and C was 311, 375, and 369, respectively.

Results

There was no significant difference in gender distribution, the proportion of left and right affected ears, and the average interval from onset to treatment among the three groups (P > 0.05). However, there were significant differences in their average age, distribution of audiogram type, and hearing loss levels among them (P < 0.01). Our study shows that there was no significant difference in average hearing threshold improvement before and after treatment in the three groups (P > 0.05). Regarding the complications, in group A, 33 patients (10.6%) had a transient vertigo attack during tympanic injection, which lasted for ~1-3 min. In group B, 20 patients (6.43%) complained of pain at the injection site, which disappeared after 1-3 days. No other complications occurred in all the other patients.

Conclusion

The addition of intratympanic or postauricular corticosteroid to systemic steroids did not result in a significant effect on hearing recovery in SSNHL. No obvious complications occur in SSNHL patients treated with intratympanic injection or postauricular injection of corticosteroid.

Clinical trial registration

[chictr.org.cn], registration number: ChiCTR2100048762.

Protective effect of anakinra on audiovestibular function in a murine model of endolymphatic hydrops

Introduction

Ménière's disease (MD), a common disease in the inner ear, is characterized by an increase in endolymph in the cochlear duct and vestibular labyrinth. The pathophysiology of the condition appears to be the immune response. Studies have shown that basal levels of the IL-1β increased in some MD patients.

Methods

Here, we used a murine model of endolymphatic hydrops (EH) to study the effect of anakinra on auditory and vestibular function. Mice were intraperitoneal injected with anakinra or saline before LPS by postauricular injection. Weight and disease severity were measured, histologic changes in auditory were assessed, and inflammation state was evaluated.

Results

We found that anakinra therapy reduced LPS-induced EH, alleviated LPS-induced hearing loss and vestibular dysfunction, and inhibited the expression of the inflammatory cytokines and macrophage infiltration in the cochlea of mice. We further demonstrated that anakinra ameliorated the disorganization and degeneration of myelin sheath, and reduced the neuron damage in cochlea of EH mice.

Discussion

Consequently, anakinra contributes to a promising therapeutic approach to MD, by restricting EH, alleviating auditory and vestibular function, inhibiting inflammation of the inner ear and protecting the cochlear nerve. Further investigations are needed to assess the potential therapeutic benefits of anakinra in patients with MD.

Is postauricular injection a systemic or a topical route for inner ear drug delivery?

The challenges associated with the blood-labyrinth barrier and unwanted systemic adverse effects severely impede the development of systemic drug administration for inner ear therapy. Previous studies have demonstrated that postauricular injection might be an alternative route for the systemic administration for inner ear therapy because it is minimally invasive and can achieve a high drug concentration in the inner ear. However, the in vivo effects remain unclear. This study aimed to compare differences in cisplatin-induced ototoxicity and systemic adverse effects between postauricular and systemic administration. Here, we compared the differences in hair cell loss, body weight change, and renal dysfunction (indicated by serum levels of blood urea nitrogen and creatinine) between these two routes of administration. The results showed that although postauricular injection of cisplatin might induce greater hair cell damage in the ipsilateral cochleae than that after intraperitoneal injection, significant hair cell damage in the contralateral cochleae as well as systemic adverse effects were also observed. Our results indicated that: (1) topical administration effects might occur in the ipsilateral inner ear following postauricular injection, and (2) systemic circulation might also be an underestimated route of drug delivery to the inner ear following postauricular injection. Overall, postauricular injection is a hybrid administration route, which simultaneously shares the features of topical and systemic administration for inner ear drug delivery.

Comparison of the Pathway to the Inner Ear Between Postauricular and Intramuscular Injection of Dexamethasone in Guinea Pigs

Background

Postauricular injection as a local therapy has been confirmed to be effective for inner ear diseases. However, the mechanism for the drugs entering the inner ears remains unknown. This study aims to compare the distribution of dexamethasone by intramuscular injection with that by postauricular injection, and explore the pathway of the drugs entering the inner ears.

Methods

An in vivo optical imaging system was used to conduct a time course observation to compare the distribution of dexamethasone by intramuscular injection with that by postauricular injection in male guinea pigs. The drug availability in the tympanic mucosa, tympanum, endolymphatic sac, and cochlea was observed by a confocal laser scanning microscope.

Results

The local fluorescent intensity by postauricular injection was significantly higher in the inner ears, and lower in partial peripheral organs, than that by the intramuscular injection. The drug metabolism by postauricular injection exhibited an obviously sustained release effect in the inner ears. Drugs by postauricular injection might enter the endolymphatic sac through the posterior auricular artery and occipital artery, as well as the connections of the mastoid emissary vein, sigmoid sinus and endolymphatic sac.

Conclusion

More drugs concentrated in the inner ear for longer therapeutic time and less systemic delivery implied more effective and less risk of side effects through postauricular injection than intramuscular injection safer for the treatment of inner ear diseases.

Postauricular injection of methylprednisolone sodium succinate as a salvage treatment for refractory sudden sensorineural hearing loss

BACKGROUND

Postauricular steroid administration has been popular for treating sudden sensorineural hearing loss. However, there are few reports on its use in patients with refractory sudden sensorineural hearing loss (RSSNHL).

AIMS

The objective of this study was to investigate the therapeutic efficacy of postauricular steroid injection as a salvage treatment for RSSNHL patients.

METHODS

This retrospective study enrolled 63 RSSNHL patients between January 2016 and January 2019. Thirty-three patients of them who have been divided into the treatment group received postauricular methylprednisolone sodium succinate injection. The remaining 30 patients who formed the control group did not receive any steroid as a salvage therapy. Improvements in hearing were evaluated between pre-salvage therapy and 3 months follow-up after salvage therapy.

RESULTS

The median hearing gain in PTA was 9.88 dB HL (quartile range 7.58, 18.65) in the treatment group and 0.90 dB HL (quartile range 0.00, 4.90) in the control group (P<0.01). According to the criteria of Furuhashi, the total percentage for effective prognosis was 48.48% (16/33) in the treatment group and 10.00% (3/30) in the control group (P<0.01). The time interval from onset to study entry was significantly and independently associated with the prognosis for RSSNHL patients (P< 0.01).

CONCLUSIONS

The present findings suggest that postauricular corticosteroid administration as a salvage treatment demonstrated better results than no treatment for RSSNHL patients. The time interval from onset to study entry was mainly the prognostic factor for RSSNHL patients. It is therefore considered that postauricular corticosteroid administration may be used as a salvage therapy for RSSNHL patients.

Postauricular injection in the treatment of all-frequency and high frequency descending sudden hearing loss: A protocol for systematic review and meta-analysis

BACKGROUND

Sudden hearing loss (SHL) is a disease, at the same time a symptom, which needs to be treated in a timely manner and counts as an emergency health problem in the Department of Otolaryngology. There are many types of sudden hearing loss and among them, the occurrence of all-frequency descending sudden hearing loss and high frequency sudden hearing loss are high. The conventional treatment for these 2 types of sudden hearing loss sometimes is not as effective as expected. Postauricular injection of glucocorticoids could be the most effective treatment method. However, the effectiveness and safety of postauricular injection of glucocorticoid needs to be assessed systematically.

METHODS

The protocol for the meta-analysis was conducted under the guidance of Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P). The aim is to undertake a systematic review and meta-analysis on the effectiveness and safety of postauricular injection of glucocorticoid to treat patient diagnosed with all-frequency and high frequency descending sudden hearing loss. We searched through the following databases: English databases (PubMed, EMBASE, Web of Science) and Chinese databases (CNKI, Wanfang databases, CBM, VIP). The final selected articles will be evaluated using Cochrane RCT evaluation criteria. Revman 5.0 will be used for data analysis. Subgroup analysis, sensitivity analysis, and meta regression will detect sources of heterogeneity. Ethics approval was not required for this protocol. The findings will be disseminated through journal articles or conference presentations.

OSF REGISTRATION NUMBER

DOI 10.17605/OSF.IO/5Q9NA.

RESULTS

Objectively, evaluate the efficacy and safety of postauricular injection of glucocorticoid in treating all-frequency descending sudden hearing loss and high frequency sudden hearing loss.

CONCLUSION

To provide evidence-based medicine for glucocorticoid treatment methods in patients with all-frequency descending sudden hearing loss and high frequency descending hearing loss.

Postauricular injection glucocorticoid in the treatment of sudden hearing loss: A protocol for systematic review and meta-analysis

BACKGROUND

Sudden hearing loss is an emergency health problem in the Department of Otolaryngology that must be treated in a timely manner, or may cause lifelong regrets. The application of postauricular injection of glucocorticoid is a popular treatment to recover patients hearing level in recent years. However, the effectiveness and safety of postauricular injection of glucocorticoid needs to be assessed systematically.

METHODS AND ANALYSIS

The purpose of the study is to undertake a systematic review and meta-analysis on the effectiveness and safety of postauricular injection of glucocorticoid to treat patient diagnosed with sudden hearing loss. We will search the following databases from the date of publication to July 1, 2020: PubMed, EMBASE, Web of Science, the Cochrane Library, CNKI, Wanfang databases, the Chinese Biomedical Literature Database (CBM), the Chinese Science and Technology Periodical Database (VIP) and the Chinese Cochrane Centre's Clinical Trial Registry Platform. Observational studies regarding the association between postauricular injection of glucocorticoid and sudden hearing loss were written in English and Chinese were included. RevManV.5.3 software will be used for meta-analysis. According to the heterogeneity of the research results, fixed effects model, random effects model, subgroup analysis, sensitivity analysis, and others will be used. Ethics approval was not required for this protocol. The findings will be disseminated through journal articles and conference presentations.

RESULTS

Objectively, evaluate the efficacy and safety of postauricular injection of glucocorticoid for sudden hearing loss.

CONCLUSION

To provide evidence-based medicine for glucocorticoid treatment methods in patients with sudden hearing loss.

OSF REGISTRATION NUMBER

DOI 10.17605/OSF.IO/N5RV3.

Steroid Administration Approach for Idiopathic Sudden Sensorineural Hearing Loss: A National Survey in China

OBJECTIVE

To optimize a protocol for the steroid administration approach for idiopathic sudden sensorineural hearing loss (ISSNHL) in China.

METHODS

A questionnaire was distributed to otolaryngologists. The data on demographics, indications for first-line and salvage treatment, such as intratympanic administration of steroids (ITS) and postauricular steroids (PAS), and procedures were analyzed.

RESULTS

74 respondents used oral steroids, 112 used intravenous injections, 10 used ITS and 6 used PAS as a monotherapy for first-line treatment, and 135 used ITS or PAS in conjunction with oral or intravenous injection as a first-line treatment. Of the 249 respondents who used ITS, 97.19% adopted it as salvage therapy. The most commonly used steroid was 0.5 ml dexamethasone at 5 mg/ml and the most common side effect was pain. Of the 174 respondents who used PAS, 94.25% used it as salvage therapy. The most commonly used steroid was 0.5 ml methylprednisolone mixed with 0.5 ml lidocaine.

CONCLUSIONS

The obtained data suggested that intravenous injection of steroids was the most popular treatment for ISSNHL and that ITS or PAS were used as a salvage treatment in China.

Effectiveness of Steroid Treatment for Sudden Sensorineural Hearing Loss: A Meta-analysis of Randomized Controlled Trials

Background:

The best way to administer steroids for sudden sensorineural hearing loss (SSHL) is still unclear. The present study was aimed at estimating the efficacy of steroids by intratympanic, systemic, and combined therapy (CT) routes.

Methods:

A systematic literature search was performed from 1950 to October 2019 for randomized controlled trials comparing the use of intratympanic, systemic, and combined steroid therapy for SSHL. The outcomes of recovery rate and pure tone average (PTA) improvement were assessed by random-effects and fixed-effects meta-analysis.

Results:

A total of 20 articles identified from 7 countries were eligible for analysis. Although no significant difference in recovery rate was observed between intratympanic steroid therapy (IST) and systemic steroid therapy (SST), IST did demonstrate better hearing improvement, as evidenced by a higher PTA than SST. Compared with SST, CT comprising IST and SST had significant recovery rate improvement. Patients treated with CT had a significantly higher PTA than those treated with SST. Through subgroup analysis based on the equivalent dose of prednisone, it was shown that CT led to a significantly higher PTA than SST only in the high-dose CT versus high-dose SST groups and moderate-dose CT versus high-dose SST groups.

Conclusion:

Moderate and high dose of CT could accelerate hearing improvement in SSHL.

Sudden Sensorineural Hearing Loss in Children: A Report of 75 Cases

OBJECTIVE

To investigate the characteristics, treatment, and prognostic factors of sudden sensorineural hearing loss (SSNHL) in children.

METHODS

Seventy-five cases (78 ears) of SSNHL in children from February 2011 to June 2016 were retrospectively analyzed. We scrutinized the clinical manifestations, audiological assessments, and serologic examinations of these pediatric cases by univariate and multivariate logistic analysis methods. The patients were divided into four groups according to their audiometric curve type: ascending, descending, flat, and profound.

RESULTS

Of the 75 patients (78 ears), 25 patients were in the ascending group (32.00%), 9 patients were in the descending group (12.00%), 17 patients were in the flat group (22.67%), and 24 patients were in the profound group (32.32%). The overall recovery rates (complete + partial + slight) of the different groups were as follows: ascending group, 96.00%; flat group, 76.47%; profound group, 50.00%; and descending group, 44.44%. The overall recovery rate of all patients was 70.67%. The multivariate logistic analysis showed that the type of audiometric curve and the interval from onset to intervention were two independent risk factors that correlated with the prognosis of SSNHL in children. Some children had positive cytomegaoviyns, rubella virus, and herpes simplex virus immunoglobulin G antibodies. Twenty-one children were treated with additional intratympanic methylprednisolone as salvage therapy and 13 of these children showed improved (complete + partial + slight) recoveries. Three children had postauricular compound betamethasone injections, but none of them showed improvement. One of three children recovered slightly after treatment with intratympanic methylprednisolone combined with postauricular betamethasone injection.

CONCLUSIONS

The prognosis of SSNHL in children is closely related to the type of audiometric curve and the onset of treatment. Intratympanic methylprednisolone and compound betamethasone injected postauricularly could be effective for SSNHL in children.

Preliminary Characterization of Extracellular Vesicles From Auditory HEI-OC1 Cells

Objectives:

Isolate, purify, and characterize extracellular vesicles (EVs) obtained from auditory HEI-OC1 cells, and evaluate their suitability for intracochlear transport and delivery of pharmacological drugs and/or pro-resolution mediators of acute inflammatory processes.

Methods:

HEI-OC1 EVs were isolated and purified using the exoEasy Maxi Kit, and their size was evaluated by nanoparticle tracking techniques. Bottom-up proteomics of the EVs, either freshly obtained or stored for up to 4 months at −20°C, was performed by LC-ESI-MS/MS. LC-ESI-MS/MS-MRM was used to measure the loading of dexamethasone inside EVs following co-incubation at room temperature for 1 hour with and without 5 minutes sonication.

Results:

Routinely, we were able to obtain purified fractions of >2 × 109 EVs/mL, with diameters varying between 50 and 800 nm. Bottom-up proteomics showed that among the most abundant EVs proteins, 19.2% were cytoplasmic, 17.2% were membrane localized, 12.3% were cytosolic, and 14.6% were nucleolar. No significant differences between fresh and stored EVs were detected. Importantly, co-incubation of HEI-OC1 EVs (1 × 108 EVs/mL) with dexamethasone (10 mM) resulted in the incorporation of 10.1 ± 1.9 nM dexamethasone per milliliter of EVs suspension.

Conclusions:

Altogether, the results suggest that EVs from HEI-OC1 cells could be advantageously used as biological nanocarriers for the delivery of specific molecules and pharmacological drugs into the inner ear.

A comparison of systemic and local dexamethasone administration: From perilymph/cochlea concentration to cochlear distribution

Different types of inner ear diseases can damage different cochlear subsites by different mechanisms. Steroids administered by different methods are commonly used for treating inner ear diseases. There is reason to believe that dexamethasone (Dex) may reach cochlear subsite targets via different pathways after administration by different methods: Intratympanic (IT), postaural (PA), and intraperitoneal (IP). The purpose of this study was to explore the cochlear concentration and distribution of Dex after administration by different methods. High-performance liquid chromatography-mass spectrometry and immunofluorescence technology were employed to measure and compare the Dex concentration in the perilymph and cochlear tissue and the cochlear distribution of Dex. IT administration resulted in higher Dex concentrations in the perilymph and cochlear tissues than those with the other administration methods. Intratympanic and postaural administration could result in higher Dex concentrations in the organ of Corti than systemic administration, but systemic administration could result in higher Dex concentrations in the stria vascularis than the other administration methods. A decreasing basal-apical gradient of Dex uptake was present in the cochlea after IT but not IP or PA administration. These results indicate that different administration methods result in different Dex distributions, which can be attributed to features of the cochlear vascular system and intracochlear diffusion. Our results provide clinicians with an experimental basis for the use of different steroid injection routes to optimize the effects on inner ear diseases with different target organs.

Postaurical injection is a systemic delivery supported by symmetric distribution of Gd-DOTA in both the ipsilateral and contralateral ears

Postaurical injection of therapeutics was recently applied in clinical practice to treat inner ear diseases based on supposed existence of a direct channel from the postaurical area to the inner ear. Doubting on the associated reports and aiming to provide evidence on the inner ear uptake mechanism, the present study tracked the dynamic distribution of gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (Gd-DOTA) in rat inner ears after postaurical injection using MRI. A targeted tympanic medial wall delivery was utilized as control. The results showed that, at the early time points after postaurical injection, Gd-DOTA distributed mainly in tissues surrounding the bulla, temporal bone and skull and neck space. In the inner ear, there was gradual uptake of Gd-DOTA on both the ipsilateral and contralateral sides with equal signal intensities. There was no sign of direct channel carrying the agent from the postaurical area to the inner ear. Targeted tympanic medial wall delivery induced significantly greater uptake of Gd-DOTA in the inner ear than did postaurical injection. At 30 min post-administration, targeted tympanic medial wall delivery yielded 4.6-folds higher signal intensity than did postaurical injection. The total dose of Gd-DOTA delivered by the targeted tympanic medial wall approach was only 0.1% of that delivered by postaurical injection. In conclusion, postaurical injection is a systemic administration, which is similar to hypodermic injection, rather than a focal delivery method. By contraries, targeted tympanic medial wall delivery induces fast and abundant uptake of Gd-DOTA in the ipsilateral inner ear without significant distribution in unwanted areas.