Study On Use of Solid Dispersion Technique to Improve the Solubility of Poorly Water-Soluble Drug

The oral route remains the most preferred and convenient method for drug administration due to its ease of use, patient compliance, and cost-effectiveness. However, the therapeutic efficacy of many drugs administered orally is often limited by their poor aqueous solubility. According to the Biopharmaceutics Classification System (BCS), a significant number of newly discovered drug candidates belong to Class II and Class IV categories, characterized by low solubility and consequently poor bioavailability. Since dissolution is the rate-limiting step for the absorption of these drugs, improving their solubility has become a major challenge in pharmaceutical formulation development.[1]

Various techniques have been employed to enhance the solubility and dissolution rate of poorly water-soluble drugs, including micronization, salt formation, complexation, use of surfactants, nanotechnology, and solid dispersion systems. Among these approaches, solid dispersion technology has emerged as one of the most effective and widely accepted methods due to its simplicity, versatility, and ability to significantly improve drug dissolution behavior.[2]

Solid dispersion refers to the dispersion of one or more active pharmaceutical ingredients in an inert hydrophilic carrier matrix in the solid state. The enhancement in solubility achieved through this technique is primarily attributed to particle size reduction, improved wettability, increased porosity, and conversion of the drug from a crystalline to an amorphous state. Hydrophilic carriers such as Polyethylene Glycol (PEG), Polyvinylpyrrolidone (PVP), Hydroxypropyl Methylcellulose (HPMC), and Poloxamers are commonly employed to prepare solid dispersions.[3]

Over the years, several methods including fusion (melting), solvent evaporation, spray drying, freeze drying, and hot-melt extrusion have been developed for the preparation of solid dispersions. These techniques have demonstrated considerable success in enhancing the dissolution rate and oral bioavailability of numerous poorly water-soluble drugs such as ibuprofen, ketoconazole, carbamazepine, celecoxib, and nifedipine.[4]

The present study focuses on the use of solid dispersion technology as a promising strategy for improving the solubility and dissolution characteristics of poorly water-soluble drugs. The study aims to provide an understanding of the principles, mechanisms, preparation methods, advantages, limitations, and applications of solid dispersion systems in modern pharmaceutical drug delivery.

Drug Profile of Carvedilol

Carvedilol is a non-selective β-adrenergic blocker with additional α₁-blocking activity used for the treatment of hypertension, congestive heart failure, angina pectoris, and post-myocardial infarction management. It has the molecular formula C₂₄H₂₆N₂O₄ and a molecular weight of 406.5 g/mol. Carvedilol lowers blood pressure and cardiac workload by blocking β₁, β₂, and α₁ receptors, resulting in reduced heart rate and vasodilation. It is a white to off-white crystalline powder with poor water solubility and high lipophilicity and is classified as a BCS Class II drug. The drug exhibits oral bioavailability of approximately 25–35%, is highly protein-bound (98%), undergoes hepatic metabolism mainly by CYP2D6 and CYP2C9, has a half-life of 6–10 hours, and is excreted through feces and urine. Due to its poor aqueous solubility, carvedilol is a suitable candidate for solubility enhancement using solid dispersion technology.[5]

MATERIALS AND METHODS

Materials

The materials used in the study included Carvedilol as the active pharmaceutical ingredient (API). Polyvinylpyrrolidone (PVP K30) was employed as a solid dispersion polymer to enhance the solubility and dissolution rate of the drug. Hydroxypropyl Methylcellulose (HPMC) served as a matrix-forming polymer to stabilize the amorphous form of carvedilol, while Soluplus® was used as a solubilizing polymer to further improve drug dissolution and bioavailability. Ethanol and methanol (analytical grade) were utilized as solvents for the preparation of solid dispersions through the solvent evaporation method and for dissolving the drug and polymers. Distilled water was used for preparing various solutions, and phosphate buffer (pH 6.8) served as the dissolution medium for in-vitro dissolution studies.

Experimental Work

Procurement of Materials

All materials required for the formulation and evaluation of solid dispersions were procured from authenticated and reliable sources. Carvedilol was selected as the model poorly water-soluble drug. Polymers such as Polyvinylpyrrolidone (PVP K30), Hydroxypropyl Methylcellulose (HPMC), and Soluplus® were used as carriers to improve the solubility and dissolution rate of the drug. Analytical-grade ethanol and methanol were employed as solvents during the preparation of solid dispersions. Distilled water and phosphate buffer (pH 6.8) were used for analytical and dissolution studies.[6]

Pre-formulation Studies

Pre-formulation studies were conducted to evaluate the physicochemical properties of Carvedilol before formulation development. These studies provide essential information regarding the drug's characteristics, stability, and compatibility with excipients, helping in the selection of suitable formulation components and optimization of formulation parameters.[7]

Drug Identification

The identity of Carvedilol was confirmed through its physical characteristics, including appearance, color, and odor. Further confirmation was achieved using spectroscopic techniques such as UV-Visible spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). The obtained spectral data were compared with standard reference values to verify the authenticity and purity of the drug.[8]

Solubility Studies

Solubility studies were carried out to determine the solubility profile of Carvedilol in various media. Excess drug was added to distilled water, phosphate buffer solutions of different pH values, and organic solvents such as ethanol and methanol. The samples were shaken until equilibrium was achieved, filtered, and analyzed using UV-Visible spectrophotometry. The results confirmed the poor aqueous solubility of Carvedilol and justified the use of solid dispersion technology for solubility enhancement.[9]

Melting Point Determination

The melting point of Carvedilol was determined using the capillary tube method to assess its purity and identity. A small quantity of the powdered drug was filled into a capillary tube and heated gradually in a melting point apparatus. The temperature range at which complete melting occurred was recorded and compared with the reported standard value. A narrow melting range indicated good purity of the drug.[10]

Drug–Excipient Compatibility Study

Drug–excipient compatibility studies were performed to investigate possible interactions between Carvedilol and the selected polymers (PVP K30, HPMC, and Soluplus®). Compatibility was evaluated using FTIR spectroscopy by comparing the characteristic peaks of the pure drug, polymers, and their physical mixtures. The absence of significant peak shifts, disappearance, or formation of new peaks indicated good compatibility and suitability of the selected excipients for solid dispersion formulation.[11]

Table 6: Key Characteristic FTIR Peaks of Pure Carvedilol

Wavenumber (cm⁻¹)	Functional Group	Explanation
3200–3500	O–H and N–H Stretching	Broad absorption peak due to hydrogen bonding and hydroxyl/amino groups present in Carvedilol.
~1700	C=O Stretching	Sharp and intense peak indicating the presence of carbonyl functional groups.
1500–1600	Aromatic C=C Stretching	Peaks corresponding to aromatic ring vibrations and carbon–carbon double bonds.

 

 

Graph : FTIR Spectrum Of Pure Carvedilol

 

 

 

 

 

 

 

 

Table 8: Percentage Yield of Solid Dispersion Formulations

Batch	% Yield
F1	88%
F2	90%
F3	92%
F4	89%
F5	91%
F6	93%
F7	90%
F8	94%
F9	96%

 

 

 

Table 9: Drug Content of Solid Dispersion Formulations

Batch	Drug Content (%)
F1	95.2
F2	96.1
F3	96.8
F4	95.5
F5	97.0
F6	97.5
F7	96.2
F8	98.1
F9	99.0

 

 

Table 10: Solubility Enhancement of Carvedilol Solid Dispersions

Sample	Solubility (µg/mL)
Pure Drug	Low (Baseline)
F1	Increased
F3	Moderate Increase
F6	High Increase
F9	Maximum Increase

 

 

 

Among all formulations, F9 demonstrated the best overall performance. It showed the highest percentage yield (96%), maximum drug content (99.0%), greatest solubility enhancement, and superior dissolution profile compared to the pure drug and other formulations. The improved performance of F9 may be attributed to the higher concentration of polymer, which enhanced drug wettability, reduced crystallinity, and promoted the formation of an amorphous solid dispersion. Therefore, F9 was selected as the optimized formulation for further studies and stability evaluation.

Solid-State Characterization

a) Differential Scanning Calorimetry (DSC) Analysis

DSC analysis was performed to evaluate the thermal behavior and physical state of Carvedilol in the optimized solid dispersion formulation (F9). The thermogram of pure Carvedilol exhibited a sharp endothermic melting peak at approximately 114.5°C, confirming its crystalline nature. In contrast, formulation F9 showed disappearance or broadening of the characteristic melting peak, indicating a reduction in crystallinity and transformation of the drug into an amorphous form within the polymer matrix.

 

 

The disappearance or broadening of the melting endotherm in formulation F9 confirms the successful formation of a solid dispersion system. This result suggests that Carvedilol was molecularly dispersed in the polymer matrix, leading to reduced crystallinity and enhanced amorphization. Such changes are associated with improved solubility and dissolution behavior of the drug.

b) X-Ray Diffraction (XRD) Analysis

XRD studies were carried out to determine the crystalline or amorphous nature of Carvedilol in the optimized formulation. The diffraction pattern of pure Carvedilol showed sharp and intense peaks, confirming its highly crystalline structure. In contrast, formulation F9 exhibited a broad halo pattern with significantly reduced peak intensity.

 

 

The broad halo pattern observed in F9 indicates a substantial reduction in crystallinity and successful conversion of Carvedilol into an amorphous form. The amorphization of the drug contributes to enhanced solubility and dissolution by increasing the free energy and molecular mobility of the drug particles. The XRD results support the DSC findings and confirm the successful formation of an amorphous solid dispersion.

c) Scanning Electron Microscopy (SEM) Analysis

SEM analysis was performed to examine the surface morphology of pure Carvedilol and the optimized solid dispersion formulation (F9). The micrographs of pure Carvedilol revealed large, well-defined crystalline particles, indicating its crystalline nature. In contrast, formulation F9 exhibited a smooth, porous, and irregular surface with the absence of distinct drug crystals, suggesting successful dispersion of the drug within the polymer matrix.

 

 

The SEM images demonstrated significant morphological changes after solid dispersion formation. The transformation from large crystalline particles to a smooth and porous structure indicates reduced crystallinity and improved drug distribution within the carrier system. The porous surface of F9 provides a larger surface area for contact with the dissolution medium, resulting in enhanced wettability and faster drug dissolution. These findings support the DSC and XRD results, confirming successful amorphization and improved dissolution characteristics of the optimized formulation

 

d) In-vitro Dissolution Study

Table 12: % Drug Release at 60 Minutes

Sample	% Drug Release
Pure Drug	~22%
F1	55%
F3	68%
F5	78%
F7	88%
F9	95–98%

All solid dispersion formulations showed significantly higher drug release than pure Carvedilol. The optimized batch F9exhibited the highest dissolution (95–98%) at 60 minutes, while the pure drug showed only 22% release. The improved dissolution was due to enhanced wettability, reduced crystallinity, decreased particle size, and strong drug–polymer interactions. Therefore, F9 was identified as the best formulation for improving the dissolution rate of Carvedilol.

e) Stability Study of Optimized Batch (F9)

The optimized formulation F9 remained stable throughout the study period with no significant changes in appearance, drug content, or dissolution behavior. Drug content decreased only slightly from 99.0% to 97.8% after 6 months, remaining within acceptable limits. The dissolution profile also showed only a minor reduction, indicating good physical and chemical stability of the solid dispersion. These results confirm that F9 possesses satisfactory stability and can maintain its enhanced solubility and dissolution characteristics during storage.

Top of Form

CONCLUSION

The present study successfully developed and evaluated Carvedilol solid dispersions to improve its solubility and dissolution rate. Preformulation studies confirmed the purity and compatibility of Carvedilol with the selected polymers. Among all formulations (F1–F9), formulation F9 showed the best performance with the highest percentage yield, drug content, solubility enhancement, and drug release (95–98%).Characterization studies using FTIR, DSC, XRD, and SEM confirmed successful dispersion of the drug within the polymer matrix and conversion of Carvedilol from a crystalline to a more amorphous form. The optimized formulation also remained stable during stability studies with minimal changes in drug content and dissolution behavior.Overall, the results demonstrated that solid dispersion technology is an effective approach for enhancing the solubility and dissolution of poorly water-soluble drugs like Carvedilol. The optimized formulation (F9) showed significant potential for improving oral bioavailability and therapeutic efficacy.

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