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INTRODUCTION
Hypertension is one of the most prevalent chronic diseases worldwide and represents the leading modifiable risk factor for cardiovascular morbidity and mortality (Wang et al., 2021). Despite the availability of multiple antihypertensive agents, control rates remain suboptimal, and hypertension continues to contribute substantially to global disease burden, accounting for nearly 9.4 million deaths annually (Lou et al., 2023; Wang et al., 2021). Current international guidelines emphasize the importance of effective blood pressure control to reduce the risk of target organ damage and cardiovascular events. Angiotensin II Receptor Blockers (ARB) are widely recommended as first-line therapy, particularly for patients with comorbidities such as diabetes, renal dysfunction, and heart failure. Azilsartan medoxomil (AZL-M), a novel ARB, has been shown to provide superior and sustained blood pressure reduction compared with other agents in its class (Baker et al., 2012). A recent systematic review and meta-analysis confirmed its efficacy and safety, demonstrating significant reductions in both systolic and diastolic blood pressure without increasing the risk of adverse events (Zhu et al.,, 2024). Among the various antihypertensive agents, Azilsartan Medoxomil (AZL-M), a prodrug of azilsartan and a selective angiotensin II type 1 receptor blocker, is widely used. However, its therapeutic efficacy is often compromised by its poor aqueous solubility (0.0037 mg/mL) and variable oral bioavailability (Chopra et al.,, 2020). Nanoparticle drug delivery systems, particularly those based on biodegradable polymers like chitosan, have gained significant attention due to their ability to enhance solubility, improve permeability, and sustain drug release (Chopra et al.,, 2019; Lou et al.,, 2023). Chitosan is a natural cationic polysaccharide with favorable biocompatibility, biodegradability, and mucoadhesive properties, making it suitable for oral and nasal delivery routes (Chakraborty et al., 2025; Hoang et al., 2022). Among the available fabrication methods, the ionic gelation technique using sodium Tripolyphosphate (TPP) as a cross-linker is simple, non-toxic, and avoids the use of harmful organic solvents. Recent studies have demonstrated that Chitosan Nanoparticles (CH-NP) not only enhance drug solubility but also provide controlled release, improved pharmacokinetics, and potential site-specific delivery chitosan nano particles. For poorly water-soluble drugs like azilsartan medoxomil, encapsulation into CH-NP can significantly improve dissolution and bioavailability, ultimately leading to enhanced therapeutic efficacy (Hoang et al., 2022; Jain et al., 2023). Azilsartan medoxomil belongs to Biopharmaceutical Classification System (BCS) Class II, characterized by poor aqueous solubility and high permeability, which limits its dissolution and oral bioavailability. The present work aims to develop and evaluate azilsartan medoxomil-loaded chitosan nanoparticles using the ionic gelation method. The study focuses on improving solubility, dissolution rate, and overall bioavailability of the drug, with a view to overcoming its biopharmaceutical limitations and providing an efficient alternative drug delivery system (De Pinho Neves et al., 2014; Mohamed et al., 2025).
MATERIALS AND METHODS
Materials
Azilsartan medoxomil, chitosan, tripolyphosphate, hydroxypropyl methylcellulose, microcrystalline cellulose, polyvinylpyrrolidone, mannitol, talc, Starch glycolate, magnesium stearate was used. Unless otherwise stated all chemicals and solvents are used in analytical grade.
Methods
Preformulation Studies
The AZL stock solution was prepared and analysed by using a double beam UV visible spectrometer (UV 1650 PC Shimadzu). The melting points of AZL were determined by the capillary method. Using a digital melting point instrument (Selec TC 303). The solubility of AZL was evaluated in various solvents including water and methanol by saturation solubility method. Drug and physical mixture compatibility were analysed through FTIR Spectrophotometer (Das et al., 2024).
Formulation and Optimization Process
Formulation of nanoparticles by ionic gelation technique and Low, medium, high molecular weight chitosan was dissolved in 1% acetic acid solution and AZL dissolved in methanol, and tripolyphosphate in water with ratio 7:3:3 for preparation of nanoparticles. Chitosan solution set on magnetic stirrer under stirring condition and add AZL solution drop by drop to chitosan solution. Then after opalescent suspension appeared then cross link with the TPP solution. The mixture was homogenized at 7000 rpm at 5mins prior to lyophilization (Van et al., 2023).
Evaluation of Azilsartan Medoxomil Nanoparticles
The average particle size, PDI and zeta potential were measured by using dynamic light scattering principle of Malvern zeta seizer (Malvern Instrument, Malvern, UK). The samples were diluted with water and placed in the disposable cuvvete and electrophoretic cell (Jassem et al., 2017; Madan et al., 2021).
Drug Content
The freeze-dried powder 10 mg would be taken in standard measuring flask and diluted with solvent which solubilize the drug (methanol for Azilsartan medoxomil). Further the stock solution is diluted with same solvent and measured in UV-visible spectroscopy to evaluate the concentration (Das et al., 2024; Tamboli et al., 2020).
Morphological Study by AFM
The surface morphology of drug entrapped nanoparticle was determined using Atomic Force Microscopy (AFM) (Ntegra-Nt-Mdt, RUSSIA). Place the sample securely onto the AFM stage or holder. The sample should be clean and flat to ensure accurate measurements, after mounting Perform system calibration, including the calibration of the AFM cantilever's spring constant, optical lever sensitivity, and other relevant parameters. Use the AFM software to position the AFM tip above the sample at a safe distance. Initiate the scanning process, allowing the AFM tip to raster across the sample surface while measuring the surface topography and collecting data (Jassem et al., 2017).
Morphological Study by SEM
Structural morphology of AZLNPs with CH:AZL:TPP weight ratio 7:3:3 was carried out using Scanning Electron Microscopy (SEM) instrument (ZEISS EVO 18, GERMANY). SEM is a constructive characterization technique that provides information on the surface features and morphology (particles’ shape, size, and arrangement) of the sample. It is comprised of a thermionic gun as an electron source along with other components (Angeli et al., 2013).
Structural Characterization by XRD
To determine the nature of AZL NPs, powder X-ray Diffraction (PXRD) analysis was performed using an Empyrean Series III diffractometer (Malvern Panalytical, UK) with Ni-filtered Cu-Kα radiation. Samples were scanned at 2θ angles ranging from 5º to 120º at room temperature in continuous mode with a step size of 0.02º/s. Changes in the diffraction peak positions of AZL were analysed to evaluate alterations in the crystal structure resulting from nanoparticle formation (Jassem et al., 2017).
Characterization of AZL-NP Tablets
The tablets were prepared (Table 1) and common quality assessment tests of tablets were conducted included weight variation, thickness and diameter, friability, disintegration test, hardness, content uniformity analysis (Jain et al., 2023; De Catrina et al., 2012).
| Sl. No. | Ingredients | Weight (in mg) |
|---|---|---|
| 1 | AZL NP | 173.91 |
| 2 | HPMC | 12 |
| 3 | MCC | 75 |
| 4 | Polyvinyl pyolidone | 15 |
| 5 | Mannitol | 87 |
| 6 | Talc | 2 |
| 7 | Starch glycolate | 15 |
| 8 | Magnesium stearate | 6 |
In vitro Drug Release Studies
Dissolution test was performed using USP apparatus 2 in dissolution testing apparatus (Labindia Instruments Pvt. Ltd., India). Azilsartan medoxomil nanoparticles using phosphate buffer (pH 6.8 and 7.4) dissolution medium of 900 mL, maintained at 37.0±0.5ºC. The paddle rotation speed was set at 75 rpm. For each formulation, six tablets were tested. At predetermined time points, 5 mL samples were withdrawn, and the samples were determined using a UV spectrophotometer (Fan et al., 2012; Madhan et al., 2023).
In vitro Drug Release Kinetics
Dissolution data of dosage form were subjected to kinetic modeling using various mathematical models, namely zero-order, first-order, higuchi, and korsmeyer peppas (Angeli et al., 2013; Ma et al.,, 2017).
Statistical Analysis
The kinetic modeling was performed using DD solver to analyze the order of drug release and type of diffusion from tablet dosage form.
Ethical Statement
Ethical approval was not required as the study is primarily in vitro physicochemical work.
Financial Support and Sponsorship Statement
The research work is completely funded by PSG College of Pharmacy, Coimbatore.
AUTHOR CONTRIBUTIONS
Both authors had contributed in research planning, work done and interpretation of data, scientific content writing. Communication of paper to the journal is covered by Subramanian somaskanthan.
RESULTS
Preformulation Studies UV analysis was performed for AZL has observed maximum lambda max followed by plotted standard curve. The melting point of AZL was found to be 214ºC determined using capillary tube method. The solubility studies observed AZL was soluble in methanol, freely soluble and very slightly soluble in water. FTIR studies conformed no physical interaction occur within the drugs and excipient mixture.
Evaluation of AZL Nanoparticles Low molecular weight showed higher positive zeta potential, lower size, and best PDI. Low molecular weight CH-NP is stable while medium molecular weight CH-NP unstable after 30 mins of preparation by deviating in the value of size, PDI and zeta potential while measuring in zetasizer.
Drug ContentDrug content for azilsartan medoxomil was 0.23 mg in 1 mg of nanoparticles.
Conversion to Solid ParticlesThe drug loaded nanoparticle is intended to freeze to -80ºC and the particles are transferred to freeze drier to sublimate the solvent for 5 days. The obtained lyophilizationproducts are characterized and loaded to tablet (Table 1).
Morphological Study by AFM Formulated nanoparticles were analysed for AFM microscopy showed nanoparticles was 162.943nm for 65536 nanoparticles analysed. Maximum size was 265.716nm, minimum size was 0 nm, Average Roughness was 26.8421nm.
Morphology Study by SEM Further, freeze dried formulated nanoparticles are analysed by the SEM analysis. It revealed that the chitosan nanoparticles exhibited irregular to semi-spherical morphology. Observed size range was approximately 325 to 788 nm (Figure 1).
Structural Characterization by XRDXRD analysis of formulated nanoparticles was performed and observed in 10 to 90º (2θ). A diffuse, broad peak is observed between 10º and 30º (2θ) as shown (Figure 2).
Characterization of AZL-NP Tablet The characterization of AZL-NP tablets, including weight variation, thickness and diameter, friability, hardness, disintegration time, and content uniformity, demonstrated that all parameters fall within their respective ideal ranges (Table 2).
| Evaluation parameter | Observed results |
|---|---|
| Weight variation test | 385.9±2.57 mg |
| Thickness | 4.2±0.075 mm |
| Diameter | 6.9±0.073 mm |
| Friability test | 0.25±0.078% |
| Hardness test | 62±2.85 N |
| Disintegration test | 14.9±0.589 min |
| Content uniformity | 95.1±0.91% |
In vitro Drug Release Studies Azilsartan medoxomil showed an extended release, with 1.17% of the drug released at 5 min and 95.85% within 60 min. These findings suggest that the release profiles of the prepared Azilsartan medoxomil tablet release were extended drug release.
In vitro Drug Release KineticsUsing DD Solver software used for in vitro drug release kinetics. The release kinetics of Azilsartan medoxomil nanoparticles tablet and Azilsartan medoxomil conventional tablets both, followed first-order release (0.8819±0.009 and 0.918±0.014 for AZL and AZL_NP respectively) and korsmeyer peppas (0.522±0.01 and 0.549±0.006 for AZL and AZL_NP respectively) model confirms a non-fickian diffusion mechanism of drug release.
DISCUSSION
In this study low molecular weight chitosan was taken in the ratio of CH: AZL: TPP as (0.1%) 7:3:3 for formulation of nanoparticles with drug (Table 3). Drug content is 100% when compared to theoretical drug content. AFM morphology of AZL-NP with 2 D image (Figure 3) indicates that the particles are irregular shape. XRD sharp peak represents crystalline nature of AZL-NP. Characterization of AZL-NP tablets are compiled with IP standard. AZl-NP are released in extended manner when compared with conventional AZL tablets. Release kinetics also proves the extended drug release with non-fickian diffusion of AZL from AZL-NP tablet.
| Items | Size | PDI | Zeta Potential |
|---|---|---|---|
| Lower | 479.4 nm | 0.239 | 34.2 mv |
| Medium | NA | NA | NA |
CONCLUSION
Azilsartan medoxomil, a poorly water-soluble BCS class II antihypertensive drug, was successfully formulated into stable chitosan-based nanoparticles to overcome its solubility limitations. Optimized nanoparticles demonstrated favorable physicochemical characteristics, with a mean particle size of 479.4 nm, a PDI of 0.239, and a zeta potential of +34.2 mV, confirming good stability. Morphological analyses (AFM and SEM) revealed spherical to semi-spherical particles with uniform distribution, while XRD confirmed partial crystallinity, supporting improved dissolution potential. Lyophilized AZL-NP was effectively converted into tablets that complied with pharmacopeial standards for hardness, friability, and disintegration. In vitro dissolution studies indicated markedly improved drug release compared with conventional tablets, including an 11-fold increase in solubility within 10 min and an 18% enhancement in dissolution rate after 1 hr. Drug release kinetics followed first-order and korsmeyer-peppas models, suggesting a non-fickian diffusion mechanism. Overall, the developed AZL-NP based formulation demonstrated significant improvements in solubility and dissolution, indicating strong potential to enhance oral bioavailability and therapeutic efficacy in the management of hypertension.