A Review on: Herbal Nasal Gel

Herbal medicines are used in traditional healthcare systems and remain an important source of compounds investigated for pharmaceutical applications. Plant-derived materials contain diverse constituents, including phenolics, flavonoids, terpenoids, alkaloids and volatile compounds. Their composition may vary with species, plant part, growing conditions, harvest, storage and extraction procedure. Consequently, the development of a herbal dosage form requires botanical authentication, appropriate extraction, quality control and reproducible formulation rather than relying on the plant name or traditional use alone. The nasal route is an accessible, non-invasive route for administering medicines intended for local action, such as treatment of selected nasal conditions, and for systemic delivery of suitable drugs. The nasal mucosa is vascularised and absorbed drugs may avoid hepatic first-pass metabolism. Nevertheless, nasal delivery is affected by mucociliary clearance, mucus, epithelial permeability, formulation volume, deposition pattern and the physicochemical properties of the active substance [1–4]. A conventional nasal liquid may drain from the nostrils or move towards the nasopharynx. Mucoadhesive gels and in-situ gelling systems have therefore been studied to increase contact between a formulation and the nasal mucosa. A successful product must balance retention with ease of administration, spreading, release and compatibility with normal nasal function. Increasing viscosity or adhesion alone does not guarantee improved drug delivery or clinical benefit [5–7].

2. Anatomy and Physiology of The Nasal Cavity

The nasal cavity is divided into right and left sides by the nasal septum. Its principal regions are the vestibule, respiratory region and olfactory region. The vestibule contains hairs that help filter larger particles. The respiratory region, which accounts for most of the nasal cavity, is lined mainly by ciliated epithelium with mucus-producing cells. Mucus traps particles, while coordinated ciliary movement transports the mucus towards the nasopharynx. This protective process is known as mucociliary clearance. The olfactory region is associated with smell and has distinct anatomical and cellular features. Formulation deposition depends on the device, application technique, nasal anatomy and properties of the preparation. Nasal mucus, pH, disease state and ciliary activity can also affect the performance of an intranasal product. A gel should not obstruct the nasal passage, cause unacceptable irritation or impair normal mucociliary function [1,2,5].

3. Concept and Types of Nasal Gel

A gel is a semisolid system in which a liquid phase is held within a three-dimensional network formed by a gelling agent. A nasal gel is designed for application to the nasal cavity and must be formulated with ingredients appropriate for intranasal use. Two broad approaches are commonly discussed:

3.1 Ready-to-use nasal gel

This formulation is a semisolid before administration and is applied using a suitable applicator or delivery system. Its viscosity and adhesion may help maintain contact with the mucosa, but high viscosity can make dosing and spreading difficult.

3.2 In-situ gelling nasal system

An in-situ gelling system is administered as a liquid or lower-viscosity preparation and undergoes sol-to-gel transition after exposure to a physiological trigger. Depending on the formulation, gelation may be triggered by temperature, pH or ions. Such systems may combine ease of administration with increased retention, but gelation, dose delivery, rheology and tolerability must be established experimentally [6,7].

4. Advantages, Limitations and Desirable Characteristics

4.1 Potential advantages

• Potentially prolonged contact with the nasal mucosa through suitable viscosity and mucoadhesion.
• Possible reduction in rapid drainage or leakage when the formulation is appropriately designed.
• Non-invasive administration and potential suitability for local delivery of compatible active ingredients.
• Formulation flexibility through the selection of polymers, vehicles and release-controlling ingredients.
• Potential use as a carrier for standardised herbal extracts after compatibility and safety have been demonstrated.

4.2 Limitations and risks

• Excessive viscosity or adhesion may hinder administration, spreading or normal mucociliary clearance.
• The nasal cavity accepts only limited volumes; dosing and delivery-device performance are important.
• Herbal extracts may vary in composition and can introduce colour, odour, insoluble matter or instability.
• Plant constituents, solvents, preservatives or other excipients may irritate nasal tissue.
• Aqueous formulations may support microbial growth and require appropriate microbiological controls.
• Longer residence time does not by itself prove greater absorption, improved symptom control or clinical efficacy.

4.3 Desirable characteristics of a nasal gel

An ideal candidate should have reproducible composition, suitable pH and osmolality, appropriate viscosity and spreadability, adequate but not excessive mucoadhesion, uniform extract distribution, acceptable release characteristics, microbiological quality, stability, a compatible container-closure system and evidence of nasal tolerability. Acceptance limits should be justified for the specific formulation; a single universal target value cannot be applied to every nasal gel.

5. Herbal Ingredients and Standardisation

A herbal nasal gel may contain a single authenticated plant extract or a combination of extracts selected for a clearly stated research rationale. Selection should consider published evidence, botanical identity, availability, extractability, chemical stability, potential allergens or irritants, compatibility with the polymer and suitability for contact with nasal mucosa. Traditional use and in-vitro pharmacological activity may justify further investigation, but neither establishes intranasal safety or efficacy.

5.1 Botanical authentication and quality

The botanical name, author citation where appropriate, family, plant part and source should be recorded. Plant material should be authenticated by a qualified person or recognised institution, and a voucher specimen should be retained where feasible. Collection, drying, storage and processing conditions should be documented. Relevant controls may include identity testing, foreign matter, moisture content, microbial limits, contaminants and extraction yield, according to the material and applicable standards.

5.2 Extraction methods

The solvent and method should be chosen according to the intended chemical profile, safety requirements and subsequent formulation. Residual solvent should be controlled when relevant. Extraction yield alone is not sufficient: the extract should also be characterised using a suitable analytical fingerprint or marker assay when feasible [8,9].

5.3 Phytochemical characterisation

Preliminary phytochemical tests may indicate broad classes such as phenolics, flavonoids, tannins, saponins or alkaloids. These tests are screening tools and generally do not identify or quantify individual compounds. Where feasible, a validated or fit-for-purpose analytical method such as HPLC, HPTLC, GC or spectrophotometry should be selected according to the expected constituents. Total phenolic content may be useful as a supplementary measure but should not be described as the content of a specific active ingredient.

6. Excipients And Polymers Used In Nasal Gels

Excipients are selected to provide the required gel structure, viscosity, compatibility, stability and delivery characteristics. An ingredient used in a topical or oral product cannot automatically be assumed suitable for intranasal administration. Grade, concentration, impurities, route-specific tolerability and regulatory status must be considered.

Polymer selection should be based on comparative data for viscosity, rheology, spreadability, mucoadhesion, release, stability and nasal compatibility. Carbopol and HPMC may be studied as candidate polymers, but their suitability and the optimum concentration must be established for each extract and formulation [6,7,10].

7. Formulation Development and Preparation

7. 1 General development workflow

1. Authenticate the plant material and document its source and plant part.
2. Select and optimise the extraction method and solvent.
3. Determine extraction yield and characterise the extract using suitable screening and analytical methods.
4. Choose polymers and excipients based on intranasal suitability and compatibility.
5. Prepare preliminary batches under controlled mixing, hydration and processing conditions.
6. Assess appearance, homogeneity, pH, viscosity/rheology and spreadability.
7. Evaluate marker content, mucoadhesion and in-vitro release where analytically appropriate.
8. Assess microbiological quality, packaging compatibility, stability and relevant nasal safety endpoints.
9. Compare batches against predefined criteria and select a candidate only when supported by the data.

7. 2 Dispersion and hydration method

For a polymer that is suitable for this method, the polymer is gradually dispersed into the selected vehicle under controlled mixing to minimise lump formation. It is allowed to hydrate according to the manufacturers or established method requirements. The extract and other compatible ingredients are then incorporated using a process that limits degradation and ensures uniformity. The pH is adjusted only when appropriate for the polymer and extract. The final preparation is checked for homogeneity, entrapped air, pH and rheological properties. Carbomer viscosity commonly depends on neutralisation and the formulation environment; the neutraliser and its quantity should therefore be optimised rather than assumed. HPMC hydration behaviour depends on grade and processing conditions. The preparation procedure should document order of addition, mixing speed and duration, temperature, hydration time, final mass or volume and any deaeration step.

7. 3 Factors influencing formulation quality

Important variables include polymer type and concentration, extract loading, pH, ionic strength, mixing conditions, temperature, hydration time, vehicle composition, preservative system and packaging. Increasing polymer concentration may increase viscosity and alter adhesion and release, but the relationship is formulation-dependent. The final product must remain deliverable at the intended dose and must not impair normal nasal function.

8. Evaluation Of Herbal Nasal Gel

Evaluation methods and acceptance criteria should be chosen according to the type of gel, the intended delivery system and applicable standards. The methods below are common development considerations; not every test is relevant to every formulation, and no result should be assumed before testing.