A Comparison between Mygind and Kaiteki positions in administration of drops to the olfactory cleft

Olfaction and drug delivery to the human olfactory airspace: current challenges and recent advances

INTRODUCTION

Olfactory function, despite its critical role in human survival and quality of life, is often underappreciated. This could be associated with the fact that symptoms of olfactory dysfunction rarely occur in isolation as they are frequently concomitant with comorbidities. Furthermore, effective treatments for olfactory dysfunction largely remain elusive, and no standardized clinical practice for treating this dysfunction currently exist, thus complicating the initiation of appropriate therapeutic modalities. Intranasal administration of topical medication targeting the olfactory cleft represents a safe, noninvasive and potentially efficacious approach, but several challenges impede effective drug delivery.

AREAS COVERED

This review highlights the importance of human olfaction, assessment of olfactory function, underlying sources of olfactory dysfunction, and challenges involved in developing long-term and effective treatment modalities, particularly in the administration of topical medication to the olfactory cleft intranasally. Advancements in both device-related and administration-related modalities designed to enhance intranasal drug delivery are discussed.

EXPERT OPINION

Clinical management typically prioritizes comorbid conditions, relegating symptoms pertaining olfactory dysfunction to ancillary concerns. Device manufacturers for intranasal administration likewise underestimate the complexity and variabilities of the nasal cavity, and how these impact drug transport. Synergistic implementation of device and formulation strategies can potentially yield enhanced olfactory cleft drug delivery.

Delivering Therapy to the Olfactory Cleft: A Comparison of the Various Methods of Administering Topical Nasal Medications

Background and objective Chronic rhinosinusitis (CRS) is an inflammatory condition affecting the nasal mucosa, and it causes olfactory dysfunction (OD) in up to 78.2% of patients. Corticosteroids are the mainstay of treatment to shrink nasal polyposis, reduce inflammation, and improve olfactory function. While many delivery methods for topical nasal corticosteroids exist, there is scarce data on the efficacy of the various medication delivery methods to the olfactory cleft (OC). In light of this, this study aimed to compare the following delivery methods to the OC: conventional nasal spray (NS), nasal drops in the Kaiteki position (KP), and exhalation delivery system (EDS). Methods We evaluated 16 sinonasal cavities from eight cadaver specimens in this study. Each sinonasal cavity was administered fluorescein dye solution via NS, KP, and EDS. Following administration, nasal endoscopy was employed to capture staining patterns in the OC. OC staining was rated with scores ranging from 0 (no staining) to 3 (heavy staining) after each administration of dye solution. Mean OC staining ratings were calculated and compared using the Kruskal-Wallis rank sum test and the Wilcoxon signed-rank test. Results The mean OC staining score for the different delivery methods was as follows - NS: 1.095 ± 1.008, EDS: 0.670 ± 0.674, and KP: 2.038 ± 1.097. Nasal drops in the KP had a significantly higher staining score compared to NS (p=0.041) and EDS (p=0.003). However, there was no significant difference in staining scores between NS and EDS. Conclusions Nasal drops in the KP are more effective at reaching the OC than NS or EDS and should be considered as a first-line modality for administering topical medications when treating OD.

Visualization and Estimation of Nasal Spray Delivery to Olfactory Mucosa in an Image-Based Transparent Nasal Model

Background: Nose-to-brain (N2B) drug delivery offers unique advantages over intravenous methods; however, the delivery efficiency to the olfactory region using conventional nasal devices and protocols is low. This study proposes a new strategy to effectively deliver high doses to the olfactory region while minimizing dose variability and drug losses in other regions of the nasal cavity. Materials and Methods: The effects of delivery variables on the dosimetry of nasal sprays were systematically evaluated in a 3D-printed anatomical model that was generated from a magnetic resonance image of the nasal airway. The nasal model comprised four parts for regional dose quantification. A transparent nasal cast and fluorescent imaging were used for visualization, enabling detailed examination of the transient liquid film translocation, real-time feedback on input effect, and prompt adjustment to delivery variables, which included the head position, nozzle angle, applied dose, inhalation flow, and solution viscosity. Results: The results showed that the conventional vertex-to-floor head position was not optimal for olfactory delivery. Instead, a head position tilting 45-60° backward from the supine position gave a higher olfactory deposition and lower variability. A two-dose application (250 mg) was necessary to mobilize the liquid film that often accumulated in the front nose following the first dose administration. The presence of an inhalation flow reduced the olfactory deposition and redistributed the sprays to the middle meatus. The recommended olfactory delivery variables include a head position ranging 45-60°, a nozzle angle ranging 5-10°, two doses, and no inhalation flow. With these variables, an olfactory deposition fraction of 22.7 ± 3.7% was achieved in this study, with insignificant discrepancies in olfactory delivery between the right and left nasal passages. Conclusions: It is feasible to deliver clinically significant doses of nasal sprays to the olfactory region by leveraging an optimized combination of delivery variables.

Spatial analysis of transnasal olfactory cleft access: a computed tomography study

Objective

To our knowledge, the spatial access of naris to olfactory cleft has not been quantified. We aimed to study the relationship and space of middle turbinate, septum, anterior nasal spine and cribriform plate to improve topical medication delivery and drug applicators.

Methods

One hundred CT scans of patients (50 males, 50 females) over the age of 18 were included. Subjects with radiographic sinonasal pathology, previous surgery, or specific variant nasal anatomy were excluded. Scans were independently reviewed and bilateral measurements on bony landmarks were taken by two blinded authors. Inter-rater reliability was analysed with intraclass correlation.

Results

The average age was 46.26 years (σ = 14.0). Average distance from the anterior nasal spine to olfactory cleft was 52.3 mm (σ = 4.2 mm), and the average length of cribriform plate was 18.8 mm (σ = 3.8) with an angle relative to hard palate averaging -8.8 degrees below parallel (σ = 5.5 degree). The widths of the olfactory cleft at anterior and posterior edges of cribriform plate were 2.3 mm (σ = 0.7 mm) and 2.0 mm (σ = 0.7 mm).

Conclusions

The findings suggest a 52.3 mm distance from the naris to the anterior border of cribriform plate. The average width along this path was 3.2 mm, suggesting devices narrower than this could potentiate direct drug delivery access.

Effect of Age and Head Position on Total and Regional Aerosol Deposition in Three-Dimensional Models of Human Intranasal Airways Using a Mucosal Atomization Device

Background: This study examined the effect of age and head position on total and regional deposition of aerosol delivered by a mucosal atomization device (MAD™) in three-dimensional (3D) models of the intranasal airways of an 18-, 5-, and 2-year-old human. Models consisted of four pieces: anterior nose and nasal cavity that was divided horizontally into upper, middle, and lower thirds. Methods: Models were tested six times at supine, supine with head backward at 45° (supine45), and sitting with head backward at 45° (sitting45). The MAD delivered saline/fluorescein aerosol into model nostrils, during static airflow. Model pieces were tested for fluorescence using a fluorometer, and deposition calculated as percent fluorescence per piece relative to its reference. Total deposition (four pieces combined) and regional deposition (four pieces separately) were calculated. Results: Age and head position had little effect on total deposition. In contrast, deposition in the upper and middle third supine45 and in the lower third sitting45 was significantly different in the 2-year-old model, compared with the two older models. In addition, some head positions significantly increased deposition in the upper, middle, and lower thirds within each model, compared with other positions. Upper deposition was significantly greater at supine45, compared with sitting45 (18-year-old) and supine45, compared with supine and sitting45 (5-year-old). Middle deposition was significantly greater at supine and supine45, compared with sitting45 (2-year-old). Lower deposition was significantly greater at sitting45, compared with supine45 (18-year-old); supine and sitting45, compared with supine45 (5-year-old); and sitting45, compared with supine45 and supine (2-year-old). Conclusions: Age and head position significantly affected regional deposition of aerosol delivered by the MAD in these 3D models. Such models might be used to study other methods for targeting intranasal regions with aerosolized medications in children and adults.

Steroids and Olfactory Training for Postviral Olfactory Dysfunction: A Systematic Review

Background: Postviral olfactory dysfunction (PVOD) is a clinical challenge due to limited therapeutic options and poor prognosis. Both steroids and olfactory training have been proved to be effective for olfactory dysfunction with varied etiologies. We sought to perform a systematic review to summarize the evidence of steroids or olfactory training for patients with PVOD.

Methods: A systematic literature review using PubMed, Embase, Cochrane Library, and Web of Science was conducted to identify studies assessing olfactory change in patients with PVOD receiving steroid or olfactory training.

Results: Of the initial 273 abstracts reviewed, 20 articles with data from 2,415 patients with PVOD were included. Treatments including topical steroids, systemic steroids, classical olfactory training (COT), modified olfactory training (MOT), and olfactory training with steroid were analyzed. Both psychophysical olfactory testing and subjective symptom scores were utilized to assess the olfactory function. The routine use of nasal steroid spray alone during the management of PVOD seems to have no positive effect on olfactory dysfunction. Direct injection of steroid or nasal steroid spray into the olfactory cleft significantly improved the olfactory function in patients with PVOD. Olfactory improvement is greater than that of the natural course of the disease with short-term COT. Patients with PVOD would benefit more from long-term COT (>12 weeks). Treatment duration, various odorants, olfactory training devices, changing the types of odors periodically, different molecular odorants, and different concentrations of odorants tended to increase the efficiency of MOT. Clinically significant improvement after olfactory training was defined as an increase of threshold, discrimination, and identification (TDI) score ≥6. From week 24 to week 36, both COT and MOT groups reached the maximum therapeutic effect regarding the number of participants achieving clinically significant improvement. A combination of local or oral steroids with olfactory training is more efficient than COT only.

Conclusion: Olfactory function in patients with PVOD was effectively improved through direct steroid administration in the olfactory cleft, COT, or modification of COT. The addition of topical steroids to COT therapy showed a tendency for greater olfactory improvement in patients with PVOD.

Liquid Film Translocation Significantly Enhances Nasal Spray Delivery to Olfactory Region: A Numerical Simulation Study

Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation and translocation after nasal spray applications were simulated for both a standard and a newly proposed delivery system. Results show that the initial droplet deposition in the olfactory region is highly sensitive to the spray plume angle. For the given nasal cavity with a vertex-to-floor head position, a plume angle of 10° with a device orientation of 45° to the nostril delivered the optimal dose to the olfactory region. Liquid wall film translocation enhanced the olfactory dosage by ninefold, compared to the initial olfactory dose, for both the baseline and optimized delivery systems. The optimized delivery system delivered 6.2% of applied sprays to the olfactory region and significantly reduced drug losses in the vestibule. Rheological properties of spray formulations can be explored to harness further the benefits of liquid film translocation in targeted intranasal deliveries.