Solubility Enhancement of Atazanavir Sulfate by Inclusion Complexation with β-cyclodextrin using Solid Dispersion Technique

 

Thamarai Selvan Dhandapani¹, Raagul Seenivasan¹, Vijayaraghavan Krishnan¹,

Vivekanandan Elango¹, Sakthi Shanmuga Jeyandar Lakshmanan¹, Balagee Muthukumar², Dhandapani Nagasamy Venkatesh¹*

¹Department of Pharmaceutics, JSS College of Pharmacy

(JSS Academy of Higher Education and Research, Mysuru), Ooty – 643001, Nilgiris, Tamil Nadu, India.

²Department of Pharmaceutical Analysis, JSS College of Pharmacy

(JSS Academy of Higher Education and Research, Mysuru), Ooty – 643001, Nilgiris, Tamil Nadu, India.

 

ABSTRACT:

Similar to other antiretroviral medications, atazanavir, is a protease inhibitor (PI) that is used to treat human immunodeficiency virus (HIV) infection. This work aimed to adopt a solid dispersion approach with β-cyclodextrin as the carrier to increase the atazanavir sulfate's water solubility. Different batches of atazanavir sulfate solid dispersions and physical mixes were produced, and the effects of carrier type and concentration on the solubility and dissolution of atazanavir sulfate were systematically examined. Various analytical techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM), were utilized to study the compatibility between the carrier and drug, and the degree of crystallinity and surface morphology of the solid dispersion to assess the increase in the solubility and dissolution rate. Studies on compatibility using FTIR and DSC revealed that there was no interaction between drug with carrier. The batch formulated employing a 1:5 ratio of drug to polymer by kneading method showed good in vitro dissolution properties over the other batches and pure drug. The drug release from the formulation was found to obey first-order kinetics and diffusion as their main mechanism of release.

 

 

 

INTRODUCTION: 

Human Immuno Deficiency Virus (HIV) has become a chronic, manageable condition thanks to the introduction of highly active antiretroviral therapy (HAART), which has greatly decreased HIV-related mortality and morbidity^1,2. Protease inhibitor (PI)-based HAART regimens still struggle with problems such as a heavy pill load, antiviral resistance, and metabolic problems like hyperlipidemia and hyperglycemia^3-4.

 

The seventh Protease inhibitor in the HIV medication family, atazanavir (ATV), may have benefits such as once-daily dosing, a distinct resistance profile, and a reduced risk of insulin resistance and lipid elevation^5,6. Due to these advantages, ATV has been effective in treating HIV patients with both recent and previous diagnoses. ATV exhibits poor aqueous solubility with a Log P (5.86), classified as BCS II of low solubility and high permeability⁷. Most of the newly discovered drugs through high-throughput screening are lipophilic in nature which hampers the development of an oral dosage form and the formulator has to choose for parenteral drug administration. The solubility is considered as one of the important phenomena that affects the delivery of various drugs. In order to exhibit better oral bioavailability, the drug should exhibit good solubility in the GIT environment and also possess good permeability to enter systemic circulation. Research has been focused on the different techniques in improving the solubility of drugs that includes, solid dispersion, co-crystallization, hydrotropy, pH adjustment and co crystallization etc.  There are different techniques were adopted to improve the solubility of drug includes hydrotropy, solid dispersion, micellar solubilization, pH adjustment and co crystallization etc^8-11. Among these techniques solid dispersion technique is widely employed in enhancing the solubility due to its industrial feasibility.

 

MATERIALS AND METHODS:

Atazanavir sulfate and β-Cyclodextrin were obtained as gift samples from Hetero Drugs, Hyderabad and Signet Chemicals, Pune, India respectively. All other reagents used in the study were of analytical reagent (AR) grade.

 

Preparation of solid dispersions:

The kneading method was used to formulate atazanavir sulfate and β-cyclodextrin solid dispersion. To form a physical mixture, the drug and carrier were mixed in various ratios (1:1, 1:2, 1:3, 1:4, and 1:5) (SDI-SDV). Ethanol and water solution (1;1) ratio was used to triturate mixture in a mortar. The resulting slurry was then heated to 45°C to facilitate complete drying. After drying, the powder was ground up and passed through a sieve with a mesh size 80 to get a uniform particle size of solid dispersion. Then, the prepared powder was kept in a desiccator for further evaluation and analysis.¹²

 

Phase solubility studies:

Five distinct concentrations of β-cyclodextrin (BCD) were generated individually for the experiment: 0.001mM, 0.002mM, 0.003mM, 0.004mM, and 0.005mM. Additionally, drug was added in quantities of 0.001M, 0.002M, 0.003M, 0.004M, and 0.005M to each BCD solution. After then, the solutions were kept at constant agitation maintained at 25°C for 24hours and their absorbance was measured. The apparent stability constant was calculated using the formula. 

Ka = Slope/S₀ (1-Slope)

 

Evaluation of solid dispersion:

FT-IR Spectrophotometry:

To investigate potential chemical reactions between a drug (Atazanavir sulfate), a polymer (β-Cyclodextrin), and their combination, an FTIR spectral matching approach was utilized. Pellets were prepared using potassium bromide for all compounds, and the resulting pellets were subjected to FTIR spectroscopy. Infrared light absorption by a sample is measured using the FTIR (Fourier Transform Infrared) spectroscopy technique, which reveals the functional groups and chemical bonds that are present in the sample. By comparing the IR spectra of individual components and their combination, it is possible to detect any changes or interactions that may have occurred. Using an FTIR spectrometer, the pellets containing atazanavir sulfate, Beta-cyclodextrin, and the mixture of the two were scanned between 400 and 400 cm^-1. This spectral range covers a broad range of wavelengths and corresponds to various functional groups present in organic compounds.¹³

 

Differential scanning calorimetry (DSC):

A differential scanning calorimeter (TA-DSC) was used to record the thermograms of the drug and the drug and carrier combination. Each sample was put into a separate aluminum pan and given 10mg before being sealed. The samples were heated between 10 and 300°C at a rate of 5°C/min. An empty pan was used as a reference.

 

Power X-Ray Diffraction studies (XRD):

Japan was used to obtain powder X-ray diffraction (PXRD) patterns. The device used Cu, K(a) radiation that was Ni-filtered and ran at 30mA of current and kV of voltage. A 0.2-inch receiving slit was chosen. The samples were examined at temperatures ranging from 2 to 40°C with scan step sizes of 0.0170(2) and 1 second.

 

SEM studies:

A thin layer of gold-palladium was applied using a sputter coater unit to the pure Atazanavir sulfate medication after being deposited on a double-faced adhesive tape. The coated sample was then subjected to analysis of its surface topography using a Scanning Electron Microscope (SEM).

 

Moisture uptake:

To evaluate the moisture uptake or hygroscopicity of the Atazanavir sulfate solid dispersion, a known mass of the sample (5g) was evenly spread over a clean Petri plate with a diameter of 10cm at room temperature (20-25°C). The sample's weight was then determined at predetermined times, including 0.25, 0.5, 1, 2, 3, and 6 hours. To ensure precision, this experiment was carried out three times. Based on the weight changes that were noticed, the percentage of moisture uptake was estimated.

 

Moisture uptake (%) = Final Weight-Initial weight × 100 / Initial weight

 

Drug content:

The solid dispersions drug content was examined using a UV technique. In this procedure, 0.8ml of methanol was used to dissolve a quantity of powder equal to 10 mg of the combination. With double-distilled water, the volume was then adjusted to 10ml. At 247nm, the solution's absorbance was measured in comparison to a control. The medication content in the solid dispersions was calculated using a specified formula.

 

Drug content (mg/ml) = (Absorbance × slope + intercept) × bath volume/1000

 

In vitro dissolution studies:

Utilizing a USP (XXII) dissolving equipment and the paddle method, dissolution investigations were carried out. The dissolution flask was filled with 900ml of freshly made double phosphate buffer, which was then allowed to warm up to 370.5°C. Size 2 firm gelatin capsules were filled with the solid dispersion, which contained an equivalent of 25mg of atazanavir sulfate, and placed in the basket before being submerged in the dissolution media. For one hour, the basket was rotated at a speed of 50rpm. Five milliliters of the dissolution medium were taken as samples at various intervals of 0, 15, 30, 45 and 60 minutes. To keep the sink conditions, an equal volume of new buffer was introduced to the medium after each withdrawal. By comparing the absorbance at 247nm of the removed samples to a blank, the amount of drug present was calculated.

 

Release kinetics:

By fitting the release profiles to the first order, Korsmeyer-Peppas, and Higuchi theoretical models, the kinetics of the MA released from inclusion complexes were ascertained:

 

F_t= 1-exp (-k₁.t)

Where K1 is the first order release constant and Ft is the amount of the drug dissolved in time t.

 

M_t/M_i= K_KP. TN

Where Mt/Mi represents the drug's fractional release into the dissolving medium, Mt represents the drug's release accumulation, and Mi represents the drug's original dosage. The release exponent ‘n’ serves as a proxy for the drug release mechanism, while KKP stands for the Korsmeyer-Peppas constant.

 

F_t= K_Ht^0.5 + a

Where K_H is a constant describing the initial drug release and an is the Higuchi release constant¹⁴.

 

RESULTS AND DISCUSSION:

Compatibility studies:

Compatibility studies were conducted to assess the interaction between Atazanavir sulfate and the selected carrier, β-Cyclodextrin, using the FTIR spectral matching approach. The analysis revealed that there were no observable changes in the appearance or disappearance of peaks in the spectra. Specific functional groups were examined to further evaluate the compatibility. The C=O stretching at 1674.88 cm^-1, NH at 3351.68 cm^-1, and ether (C=C) bonds at 1533.3 cm^-1 were found to be present, indicating that the hydroxyl groups remained unreacted. Additionally, the presence of C-H bonds at 3056.62 cm^-1 provided further evidence of the non-reactivity between the drug and the carrier. These results indicate that the drug and the carrier were compatible with each other. The formation of a complex between Atazanavir sulfate and β-Cyclodextrin was further examined using a phase solubility diagram, as depicted in Figure 2. The plot showed that the drug's water solubility increased linearly as β-Cyclodextrin concentrations increased. The apparent stability constant for the drug in the complex formation was determined to be 134.66, indicating a favorable interaction between Atazanavir sulfate and β-Cyclodextrin.

 

Phase solubility studies:

Five distinct concentrations of beta-cyclodextrin (BCD) were generated individually for the experiment: 0.001 mM, 0.002mM, 0.003mM, 0.004mM, and 0.005mM. Additionally, Atazanavir sulfate was added in quantities of 0.001M, 0.002M, 0.003M, 0.004M, and 0.005M to each of the BCD solutions. After then, the solutions were not touched for 24hours. After 24hours, the solutions' absorbance was assessed.

 

Ka  = Slope / S₀ (1-Slope)

 

 

Figure 1. Phase solubility studies for Atazanavir sulfate

 

Preparation and characterization of solid dispersion:

Five different batches of solid dispersions were prepared using kneading method, the drug and carrier were combined in ratios of (1:1, 1:2, 1:3, 1:4, and 1:5) and coded as SD-I to SD-V. The resulting solid dispersions underwent a comprehensive assessment involving measurements of average particle size, angle of repose, bulk density, moisture absorption, drug content, and in vitro dissolution behavior. The angle of repose values for the kneaded mixtures ranged between 21 and 24 degrees, signifying favorable flow characteristics. The kneaded mixtures' bulk density values fluctuated from 0.80 to 0.88g/cc. The compressibility values, in the range of 15-19%, indicated an optimal level for tablet formulation. Moisture uptake ranged from 6% to 7% for the kneaded mixtures, suggesting a hygroscopic nature of the powder. Drug content, assessed using kneading, spanned from 95% to 98%.

Table 1: Evaluation of solid dispersions of Atazanavir sulphate

Properties	Code of Formulation
	SD-I	SD-I	SD-I	SD-I	SD-I
Percentage yield (%)	98±1.4	95±1.5	99±1.5	97±1.7	98±1.6
Angle of repose (0)	21±1.3	22±1.4	24±1.1	23±1.5	24±1.1
Bulk density(g/cc)	0.86±0.01	0.87±0.04	0.87±0.03	0.88±0.05	0.80±0.06
Compressibility (%)	16±1.5	17±1.5	15±1.4	19±1.6	18±1.4
Moisture uptake (%)	6±1.5	6±1.5	7±1.4	6±1.6	7±1.2
Drug content (%)	98±1.1	96±1.2	95±1.6	97±1.4	96±1.7

(n=3±SD)

 

FT-IR Spectrophotometry:

An FTIR spectral matching approach was used to look into possible chemical interactions between the drug and polymer. For each component, potassium bromide pellets were made, and these pellets were then exposed to FTIR spectroscopy in the 4000-400 cm-1 range using an FTIR spectrometer. Additionally, individual material samples of Atazanavir sulfate, β-Cyclodextrin, and the combination of Atazanavir sulfate and β-Cyclodextrin were also analyzed using FTIR spectroscopy. The obtained IR spectra provide valuable information about the presence of any chemical interactions between the drug and polymer. Furthermore, thermograms showing the thermal behavior of the samples are presented in Figures 2 and 3.

 

 

Figure 2. FT- IR of Atazanavir Sulfate

 

 

Figure 3. FT-IR Atazanavir Sulfate with β-Cyclodextrin

DSC Study:

DSC study revealed the presence of single endothermic at a temperature of 200.9°C. This peak was also observed with the drug and carrier mixture, suggesting no interaction between the drug and the carrier employed. The DSC thermograms are shown in  figure 4 and 5.

 

 

Figure 4. DSC Thermogram of Atazanavir sulfate

 

 

Figure 5. DSC Thermogram of Atazanavir sulfate with β-Cyclodextrin

 

X-Ray Diffraction Studies (XRD):

The X-Ray Diffraction (XRD) spectra of atazanavir sulfate in its purest form, atazanavir sulfate combined with ß-CD, and atazanavir sulfate alone are shown in Figures 6 and 7. Changes in the drug's crystal structure can be seen by contrasting the diffraction spectra of the solid dispersion, pure drug, carrier, and their mixing. As observed in the figure, the XRD pattern of Atazanavir sulfate + ß-Cyclodextrin exhibits broadened peaks, indicating a lower degree of crystallinity. At specific 2θ angles (10.37, 22.25, 23.78, 24.42), the peaks are overall amorphous with a poor crystalline structure present in the mixture. These findings suggest that the inclusion of ß-Cyclodextrin in the solid dispersion has altered the crystalline nature of Atazanavir sulfate, resulting in reduced crystallinity and increased amorphous character.

 

 

Figure 6. X-Ray Diffraction of Atazanavir sulfate

  

 

Figure 7. X-Ray Diffraction (XRD) of Atazanavir sulfate and β-

                                                                                                                              Cyclodextrin:

Scanning Electron Microscopy Studies (SEM):

The scanning electron microscope (SEM) image of Atazanavir sulfate reveals its crystalline properties. However, when the binary mixture is observed in SEM images, it becomes evident that the mixture contains more agglomerates than the crystalline form of Atazanavir sulfate. This difference in structure contributes to the enhanced solubility of Atazanavir sulfate (Figures 8 and 9)

 

 

Figure 8. SEM of Atazanavir sulfate  

 

Figure 9. SEM of Atazanavir sulfate with β-Cyclodextrin

 

In vitro dissolution studies:

The dissolution studies for the in vitro assessment were conducted using the USP (XXII) dissolution apparatus, employing the paddle method. Pure drug and solid dispersions were examined, utilizing a phosphate buffer with a pH of 7.4 at a temperature of 37±1^oC. At predetermined intervals of 0, 0.25, 0.50, 0.75, and 1 hour, samples were taken and the same quantity of fresh buffer was replaced to maintain sink condition. The findings showed that at the 60 minutes, the drug release from the solid dispersion made using the kneading method was 30.12% (SD-I), 64.21% (SD-II), 51.71% (SD-III), and 53.82% (SD-IV). Notably, a release of 95.42% was observed for the solid dispersion with a ratio of 1:5 (SD-IV), in comparison, the pure drug exhibited a release of only 15.32% at the end of 60 minutes.

 

 

Figure 10. In vitro dissolution study of Atazanavir solid dispersion F-I (■), F-II (▲), F-III (x), F-IV (*), F-V (●) and pure drug (♦)

 

Table 1: Release kinetics of Atazanavir solid dispersion

Code of Formulation	Zero		First order		Higuchi	Korsmeyer Peppas
	r2	Slope	r2	slope	r2	r2	Slope
SD1	0.8925	29.932	-0.91053	-0.15928	0.98364	0.971236	0.345029
SD2	0.978944	3.458101	0.976754	2.018713	0.990594	0.961326	1.125217
SD3	0.993489	2.0045784	0.99918	1.31819	0.997457	0.999002	0.808521
SD4	0.984951	1.20786	0.993434	1.028392	0.99467	0.994995	0.686325
SD5	0.962975	1.478312	0.998208	2.708919	0.984896	0.985575	0.330219

 

CONCLUSION:

This study aimed to produce a solid dispersion of atazanavir sulfate using β-cyclodextrin as a carrier. Atazanavir sulfate was selected as the drug due to its limited solubility in water, and β-cyclodextrin was employed as the carrier. Compatibility studies conducted using FTIR demonstrated that the drug and carrier were compatible, with no observed interactions between them. The solid dispersions prepared using the kneading method were assessed. Based on the findings of the aforementioned studies, it was determined that the batch prepared with a drug-to-polymer 0ratio of 1:5 using the kneading method exhibited a 6.22 fold increased solubility in vitro dissolution performance than pure drug. Through DSC studies, it can be inferred that a chemical complexation occurred between the drug and the carrier, likely contributing to the improved solubility of the drug. X-ray diffraction (XRD) studies revealed an overall amorphous form with a diminished crystalline structure in the mixture, indicating the conversion from crystalline to amorphous form. As a result, it may be said that the medication's solid dispersion complex showed a better dissolving profile than the pure drug. Atazanavir sulfate dosage can be decreased as a result, which might lessen side effects and increase bioavailability.

 

ACKNOWLEDGEMENT:

The authors would like to thank the Department of Science and Technology- fund for the improvement of Science and Technology infrastructure in Universities and Higher Educational Institutions (DST-SIST), New Delhi for their infrastructure support to our department

 

CONFLICTS OF INTEREST:

The authors declare no conflict of interest in this study.

 

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Received on 03.03.2024      Revised on 30.09.2024 Accepted on 27.02.2025      Published on 13.01.2026 Available online from January 17, 2026 Research J. Pharmacy and Technology. 2026;19(1):1-6. DOI: 10.52711/0974-360X.2026.00001 © RJPT All right reserved
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