Current Trends on Solid Dispersions: Past, Present, and Future

Solid dispersions have achieved significant interest as an effective means of enhancing the dissolution rate and thus the bioavailability of a range of weakly water-soluble drugs. Solid dispersions of weakly water-soluble drugs with water-soluble carriers have lowered the frequency of these problems and improved dissolution. Solid dispersion is a solubilization technology emphasizing mainly on, drug-polymer two-component systems in which drug dispersion and its stabilization is the key to formulation development. Therefore, this technology is recognized as an exceptionally useful means of improving the dissolution properties of poorly water-soluble drugs and in the latest years, a big deal of understanding has been accumulated about solid dispersion, however, their commercial application is limited. In this review article, emphasis is placed on solubility, BCS classification, and carriers. Moreover, this article presents the diverse preparation techniques for solid dispersion and gathers some of the recent technological transfers. The different types of solid dispersions based on the carrier used and molecular arrangement were underlined. Additionally, it summarizes the mechanisms, the methods of preparing solid dispersions, and the marketed drugs that are available using solid dispersion approaches.


Introduction
e oral route is the most convenience route for drug adminstration and favore mode of delivery [1]. From the patient's standpoint, swallowing and medication is a comfortable and familiar method of taking medication. As a result, orally delivered drugs are often more effective than alternative modes of administration, such as parenteral, in terms of patient compliance and drug treatment. When an active substance is given orally, it must first dissolve in the stomach and/or intestinal fluids before it can pass through the GI tract's membranes and reach systemic circulation [2]. erefore, water solubility and/or membrane permeability of the drug molecule are significant contributors to drug absorption from the gastrointestinal (GI) tract, which causes low medication bioavailability of the medications. Consequently, a drug with weak aqueous solubility usually shows a dissolution rate of limited absorption, while a drug with weak membrane permeability usually shows a permeation rate of limited absorption [3].
Pharmaceutical scientists have two approaches to improving the oral bioavailability of pharmacologically active agents: (i) improving the solubility and dissolution rate of poorly water-soluble medications, and (ii) improving the permeability of poorly permeable drugs [4].
In the pharmaceutical literature, a variety of strategies have been used to improve the dissolving capabilities of weakly water-soluble medications other than solid dispersions. Some of these strategies are salt creation, complexation with cyclodextrins, solubilization of pharmaceuticals in solvent(s), and particle size reduction; however, each of these procedures has significant limitations, such as poor yield, expensive, time consuming, and very low drug solubility [5]. On the other hand, formulating pharmaceuticals as solid dispersions provides several processing and excipient alternatives, allowing for greater flexibility for formulating oral delivery systems of poorly tolerated water-soluble medications [6].
Much of the research that has been published on solid dispersion technologies includes medications that are poorly water-soluble and highly permeable to biological membranes as with these drugs dissolution is the rate-limiting step to absorption. As a result, the rate of in vivo absorption will be enhanced in tandem with an increase in the drug dissolution rate. Medications having limited water solubility and strong membrane permeability are classified as class II drugs in the biopharmaceutical classification system (BCS). As a result, solid disperion technology has many promises to enhance the oral absorption of BCS Class II drugs and thier bioavailability [7]. e weak solubility of many discovered drugs is a barrier to their possible therapeutic activity. According to statistical reports, it has been estimated that 40 per cent of the novel chemical entities identified today are water-insoluble [8]. Unfortunately, many of these prospective medications are abandoned in the early phases of development due to solubility difficulties. As a result, it is becoming increasingly crucial to identify new ways to overcome solubility limits so that the potential therapeutic benefits of these active compounds can be realized [9].
Solid dispersion formulation is one of the most promising and practical approaches for increasing solubility. According to Chiou and Riegelman [3], solid dispersion systems are "the solid-state dispersion of one or more active substances in an inert carrier or matrix generated by the fusion, solvent evaporation, or melting-solvent process." Matrix is hydrophilic, whereas the medication is hydrophobic. Simple eutectic mixtures, solid solutions, glass solutions, and glass suspensions, amorphous precipitation in a crystalline carrier, compound, or complicated forms are solid dispersion types [3].

Solubility
At a particular temperature and pressure, the solubility of a substance is the amount that has entered the solution when an equilibrium is reached between the solution and the excess, that is, an undissolved substance. e dissolved substance is referred to as the "solute," and the dissolving fluid in which the solute is dissolved is referred to as the solvent, and the two together are referred to as the solution [10]. Table 1 lists the definitions of various solubility terms.

Biopharmaceutical Classification System (BCS)
. e biopharmaceutical classification system was first devised in 1995 by Amidon and his co-workers [7]. According to the biopharmaceutical classification system, drug substances can be classified as shown in Table 2.
Bioavailability may be improved by enhancing the solubility and dissolving rate of the class II medication in the gastrointestinal fluids. Medication release is a critical and limiting step for oral drug bioavailability, especially for medicines with limited gastrointestinal solubility. Optimizing the drug release profile of these drugs makes it feasible to improve their bioavailability and reduce side effects [11,12].
e World Health Organization's (WHO) model list of essential medicines has assigned a biopharmaceutical classification system categorization based on publicly available data. Unfortunately, only 61 of the 130 orally given medications on the WHO list could be classified with accuracy. Eighty-four percent of these medications are classified as class I, seventeen percent as class II, forty-nine percent as class III, and ten percent as class IV [10].

Mechanisms Involved in Enhancing Drug Solubilization by Solid Dispersion Technique.
Although the mechanism is not well understood yet, the basic principle includes the complete removal of drug crystallinity and molecular dispersion of the poorly soluble compound in a hydrophilic polymeric carrier [13]. When the solid dispersion is exposed to the aqueous media, the carrier dissolves and the drug is released as fine colloidal particles. is increases the surface area of the dissolution rate and hence the bioavailability of poorly water-soluble drugs. e drug is a soluble hydrophilic carrier and has a better dissolution rate due to the reduction of the particle size and the increase of the particle porosity. e potential advantage of this technique is enormous. Recently, surfactants were included to improve formulations, as in many cases. However, thermodynamic instability and recrystallization of the drug became a problem. Hence, surfactants are used to avoid recrystallization and to potentiate their solubility [14].

e Justification behind the Use of the Solid Dispersion
Technique in the Pharmaceutical Industry. e primary purposes of using this technique in pharmaceuticals are [15] Figure 1 summarizes the different types of solid dispersion.

Based on the Carrier Used.
A carrier must meet the following criteria to be appropriate for enhancing the dissolution rate of a drug. Materials used as carriers are given in Table 3.
(i) freely water-soluble with intrinsic quick-dissolving capabilities (ii) nontoxic and pharmacologically inert (iii) e melting process must be heat stable and it should have a low melting point (iv) It must be soluble in a wide range of solvents (v) It should be able to preferably increase the aqueous solubility of the drug (vi) Ideally, it should be able to boost the medication's water solubility and be chemically compatible with the drug and should not form a firmly bound complex with it [17] Based on the carrier used, solid dispersions can be classified into the following four generations [18]: First generation: Solid dispersions were formed as the first carriers to be applied in solid dispersions [19]. In this generation, crystalline carriers are used such as sugars and urea. e disadvatange of the first generation is the presence of crystalline nature of the carrier. In which they are thermodynamically stable, and the drug will not be released as fast as the amorphous form [20]. Second generation: is generation involves the use of amorphous carriers which are usually polymers [21]. ese polymers could be synthetic such as polyethene

Types of Solid Dispersions
On the basis of the carrier used [8] First generation Second generation ird generation

Fourth generation
On the basis of their molecular arrangement [9] Eutectics Systems

Solid Solutions
Amorphous precipitation in a crystalline carrier Figure 1: Schematic representation of the solid dispersion types [15]. Advances in Pharmacological and Pharmaceutical Sciences glycols (PEG), povidone, polyvinyl pyrrolidine, and polymethacrylates or natural-based polymers, such as ethyl cellulose, hydroxypropyl methylcellulose (HPMC), and starch derivatives such as cyclodextrins or hydroxypropyl cellulose [22]. ird generation: It has been proved that the dissolution profile can be enhanced by using a carrier with surface active agent properties. As a result, the use of surface-active agents such as poloxamer 407, compritol 888, ATO, inutec SP1, gelucire 44/14, and inulin as carriers was revealed to be effective in achieving a high purity level of the polymorphic and for increasing in vivo bioavailability [23]. Fourth generation: is type of dispersion is described as controlled release solid dispersion. It contains poorly watersoluble drugs with a short biological half-life. e carriers used are either water-soluble carriers or insoluble water carriers. Solubility enhancement and extended drug release in a controlled manner are the two targets in controlledrelease solid dispersion. e water-soluble carriers used in controlled-release solid dispersion include ethyl cellulose, Eudragit, Hydroxypropyl cellulose, and others [24]. is mixture composes of two compounds in the liquid state that are completely miscible but in the solid state only to a very limited extent. It is prepared through fast solidification of the fused melt of the two compounds, giving a complete liquid miscible product and very little solid-solid solubility. Such a system is thermodynamically intimately mixed with the physical mixture of its two crystalline compounds [26].

Glass Solution and Suspensions. Glass solution refers
to the homogeneous glassy system in which a solute is dissolved in a glass carrier, whereas the glass suspensions, in which the precipitated particles are present, are suspended in glass solvent. e lattice energy in such systems is low, and the melting point is not sharp, examples of carriers that form glass solutions and suspensions are urea, citric acid, polyethene glycol, polyvinyl pyrrolidine, and sugars such as dextrose, sucrose, and galactose [26].

Solid Solution.
In this system, when the two components crystallize together, they form a single homogeneous phase system. e drug particle size is decreased to its molecular size in the solid solution. As a result, a faster rate of dissolution will be achieved in the solid solution than in the corresponding eutectic mixture. e solution can be categorized (as continuous or discontinuous) depending on the level of miscibility of the two compounds or how the solvate molecules are circulated (substitutional, interstitial, or amorphous) [26].   Advances in Pharmacological and Pharmaceutical Sciences (i) Continuous solid solutions: e components are miscible in all proportions in a continuous solid solution. Hypothetically, this indicates that the bonding strength between the two components is greater than the bonding strength between the molecules of each individual component. However, solid solutions of this type have not been reported in the pharmaceutical world to date [27].
(ii) Discontinuous solid solutions: In the case of discontinuous solid solutions, the solubility of each component in the other component is limited [27]. (iii) Substitutional solid solutions: is type of solid solution occurs only if the size of the solute molecules is variable by less than 15% or so from the solvent particles [28]. (iv) Interstitial solid solutions: In interstitial solid solutions, the soluble particles fill the interstitial gaps between the solvent molecules in the crystal lattice. erefore, the solute molecule diameter should be less than 0.59 times that of the solvent molecular diameter [28].

Amorphous Precipitation in the Crystalline Matrix.
In the crystalline carrier, the drug may also precipitate in an amorphous form instead of simultaneous crystallization of the drug and the carrier (eutectic system). High dissolution rates are usually produced in this form because of the high energy of the drug in the amorphous state [25].

Method of Preparation
Several techniques for preparing solid dispersion are listed in Figure 3. Generally speaking, there is no best method in solid dispersion to enhance poorly water-soluble drugs. It depends on factors such as the hydrophilicity-hydrophobicity balance of the drug, drug dose, and drug molecular weight. erefore, trial and error is the best approach the check the proper method that could enhance the drug solubility.

Fusion.
Sekiguchi and Obi proposed the fusion method in 1961, also known as the melt method. A physical mixture of drug and polymer is heated to generate a molten mixture, which is then cooled and hardened while vigorous stirring is performed. To reach the desired particle size, the solid mass is crushed, pulverized, and sieved. Despite its popularity, several drawbacks to employing this process in making solid dispersions are present. ese drawbacks include a lack of drug-polymer miscibility at the heating temperature. However, surfactants may be used to avoid this issue. Additionally, medications and polymers must be thermally stable at melting temperatures, therefore lower production temperatures are desirable. In addition, the fused mixture must be resistant to recrystallization and phase separation [11]. Table 4 shows examples of decent case studies for the preparation of solid dispersion using the fusion method.

Hot-Melt Extrusion Method.
e hot-melt extrusion method is the modern version of the fusion method in which the extruder induces intense mixing of the components. Compared with the traditional fusion method, melt extrusion offers the potential to shape the molten drug-polymer mixture into implants, pellets, or oral dosage forms [4]. However, this method requires the complete miscibility of the drug and the polymer in the molten state. Solubility parameter phase diagrams can be used to predict miscibility and to rationally select the compatible polymer [11].
is process has various advantages, which includes the following [11]: (1) Fewer processing steps because the components are not compressed and the product is not dried, making this procedure simple, continuous, and efficient. (2) Entire mixing at a high shear rate and temperature disaggregates the particles, resulting in a uniform distribution of tiny drug particles in the polymer matrix and molecular level dispersion. (3) In addition, unlike the classical fusion approach, this technique allows for continuous manufacturing, making it appropriate for large-scale production. HPMC, HPMCAS, PVP, PVP, vinyl acetate, and polyethylene oxide are some of the most often utilized polymeric materials in hot-melt extrusion [4].
Over the last decade, hot-melt extrusion (HME) has developed as an effective technique for drug delivery and has started to host such molecules previously considered unviable as drugs. Hot-melt extrusion is an efficient technology for creating solid molecular dispersions and has been proven to produce sustained, modified, and targeted drug delivery after improved drug bioavailability [34]. Nonsteroidal antiinflammatory drugs (NSAID) and paracetamol were Advances in Pharmacological and Pharmaceutical Sciences prepared as orally disintegrating tablets using the hot-melt extrusion method [35]. Paracetamol was prepared using the hot-melt extrusion method through granulation paracetamol and filler excipients with different low molecular weight polyethylene glycol using the hot-melt extrusion process. e granules achieved were then mixed with disintegrants and lubricant and were compacted into tablets. e HME granules showed an enhanced drug release profile as compared to the original tablets. More than 80% of the drug was released by tablets that contained 15% of polyethylene glycol within 30 minutes [36], which is the needed amount for paracetamol tablets in the USP 30.

Coprecipitation Method (Coevaporate).
e carrier is accurately weighed and dissolved in water, while the medication is dissolved in an organic solvent. e aqueous carrier solution is then added to the organic drug solution after complete dissolution. After that, the solvents are ejected. e dispersion is crushed, sieved, and dried using a pestle and mortar [37]. Figure 4 shows a demonstration of the process. Table 5 shows examples of decent case studies for the preparation of solid dispersion using the fusion method.
Ibuprofen is one of the examples of medication that undergoes solubility enhancement using a coprecipitation process. e solubility and the dissolution rate were improved by two-fold and one-fold, respectively.

Solvent Method.
e solvent approach entails dissolving both the medication and the polymer in a single solvent and then removing the solvent to create a solid dispersion. is method allows for molecule-level mixing, which is favored for improving product solubility and stability [37]. e fundamental advantage of this approach is that it avoids drug and polymer thermal degradation, which is common when organic solvents are evaporated at low temperatures. When utilizing this strategy, however, formulation scientists face two obstacles [48]. e first issue is  Figure 4: Schematic presentation coprecipitation process [37].
to combine the medication and the polymer in a single solvent, which can be challenging if the polarity differences are large. Surfactants are sometimes developed to facilitate medication or polymer solubility in certain solvents. However, their amount in the final dosage form is frequently large, reducing drug loading capacity and potentially causing issues if they are not well tolerated in the body. In addition, this method is expensive due to the necessity to evaporate a substantial amount of the solvent [40]. e second issue is phase separation, which can occur when the solvent is removed. e solution is usually dried by vacuum drying. A rotary evaporator is sometimes used to accomplish rapid drying. e use of higher drying temperatures reduces the time for phase separation. e high molecular mobility of medicine and polymers at high temperatures may speed phase separation [37]. Table 5 shows examples of decent case studies for the preparation of solid dispersion using the solvent evaporation method.
One study was performed with furosemide as it had limited bioavailability, poor solubility, and permeability. e research study intended to assess coprecipitation, kneading, and solvent evaporation by solubility and dissolution enhancement methods. All the approaches were found to enhance the solubility to some extent; however solvent evaporation gave the best results. However, the following order was observed; solvent evaporation > kneading > physical mixtures > coprecipitation [49].

Spray
Drying. Spray drying has become a prominent processing method for creating solid drug dispersions. It is used to turn a liquid or a suspension into a dry powder in one step. is method allows for more precise control of process factors, resulting in powders with the required size, shape, density, flow characteristics, and crystalline forms [50]. In spray drying, the solvent evaporates at a rapid rate, resulting in a dramatic increase in viscosity and trapping of drug molecules in the polymer matrix. Drugs with limited water solubility can be spray-dried into extremely fine particles if they are soluble in certain spray-drying solvents. However, the chemical properties of the medication influence the nature of the solid particles generated and spray drying can result in amorphous material, crystalline forms, imperfect crystals, or metastable crystals. Indeed, Mahlin and Bergstrom [51] studied various drug compounds and found that developing an amorphous form is more dependent on the chemical composition of the medications than on process variables. However, the stability of the amorphous forms depends on the process variables. Spray drying provides excellent control over powder characteristics, and it has become the most popular solvent-based production process due to lower manufacturing costs, simplicity of scaleup, and continuous batch production. Table 6 shows a few examples of decent case studies for the preparation of solid dispersion using the spray drying method.
One study used solid dispersion (SD) techniques and modified the locust bean gum (MLBG) as a carrier to enhance lovastatin drug solubility. Solubility and dissolution studies were used, respectively, to examine the effects of polymer concentration and preparation methods on solubility enhancement. According to the solubility study's findings, lovastatin's solubility increased as MLBG concentration increased. It was discovered that the method used for making the solid dispersions affected the dissolution rate of lovastatin. According to dissolution research, among the different ways of preparing solid dispersions, modified solvent evaporation is the most practical and successful method for improving the solubility of weakly water-soluble lovastatin. e kneading method improves the dissolution rate better than that of coprecipitation because it has other trituration influences on the drug. Spray drying improves the dissolution rate of lovastatin due to enhanced wettability of drug particles and a significant decrease in particle size in the spray drying procedure. e explanation for the greater dissolution rate of solvent evaporation in comparison with Advances in Pharmacological and Pharmaceutical Sciences 7 other solid dispersions could be due to the availability of increased surface area of particles in the suspension [46].

Supercritical Fluid (SCF)
Method. Supercritical fluids have both liquid and gas characteristics. Materials exhibit liquid-like solvent characteristics and gas-like viscosity, diffusivity, and thermal conductivity under supercritical conditions. While the solvent properties are advantageous for drug/polymer solubilization, the gas-like properties considerably improve the fluids' mass transport characteristics [55]. is approach is most commonly used with supercritical carbon dioxide (CO 2 ) as a drug and polymer solvent or as an antisolvent. e polymer and medicine are dissolved in supercritical CO 2 and blasted into a lowpressure zone through a nozzle, generating adiabatic CO 2 expansion and fast cooling. As a result, this approach enables the creation of drug particles with much smaller particle sizes. e rapid expansion of supercritical solutions is the common name for this technology (RESS) [56]. Current supercritical fluid approaches have shown the ability to generate nanoparticulate suspensions of particles with sizes ranging from 5-2000 nm. is process is considered environmentally friendly because it does not require the use of organic solvents and the small amount of residual CO 2 trapped inside the polymer causes no risk to patients. CO 2 's propensity to plasticize and swell polymers can also be exploited. However, the limited solubility of most medicinal chemicals in CO 2 prevents this method from being used in practice. Several supercritical fluid-processing approaches have been developed to address specific parts of these flaws and to increase solubility. ese approaches involve precipitation with a compressed antisolvent, supercritical fluidenhanced dispersion, supercritical antisolvent processes, gas antisolvent recrystallization, and an aerosol supercritical extraction system [57]. e drug solubility in supercritical CO 2 has a huge effect on the diameter ranges of the particles formulated by the RESS process. is was demonstrated in a study by Kim et al. [58] when they utilized RESS for the formulation of ultrafine drug particles by applying supercritical CO 2 , with no organic solvent. ree different drugs were used (lidocaine, griseofulvin, benzoic acid) with various solubilities in supercritical CO 2 , and orifice disks and capillary tubes were fitted as an expansion apparatus. e drug solubilities in supercritical CO 2 and the impacts of different operating parameters on the physical characteristics of the particles formulated by the RESS procedure were experimentally studied. e results showed that the average particle diameter reduced with the solubility for all the drug substances and operating conditions. Response surface methodology was utilized for the optimization of the outcomes, and it was shown that the smallest particle size may be achieved at a temperature of 50°C, a pressure of 17.7 MPa, and a spray distance of 10 cm [59].

Kneading Method.
In a glass, a mixture of precisely weighed medication and carriers is wetted with a solvent and is thoroughly kneaded for sometime [16]. In the kneading method, the liquid (which may be water or a hydroalcoholic mixture) is added dropwise while the drug and polymers are triturated in a pestle and mortar. is results in the formation of a slurry and the reduction of particle size, which increases bioavailability because of the kneading action. en, the mixture is dried and placed through the mesh to bring the contents into homogeneity [60]. Satranidazole-cyclodextrin complexes were made. Following the examination of this complexation, it was discovered that there had been a noticeable increase in solubility [61]. In one study, Olmesartan medoxomil inclusion complexes were created using the kneading approach and were introduced as mouth-dissolving tablets. Complexation increased the solubility and the mechanical stability of the tablets as well as their solubility and dissolution [62]. Efavirenz in PVP K-30 was prepared by two methods, that is, kneading and conventional solvent methods. e two formulations were characterized by DSC, FT-IR, SEM, XRD, and dissolution profile.
A higher dissolution rate has been seen in solid dispersions made by the kneading technique [63]. By kneading approach, Patel created etoricoxib-cyclodextrin complexes. For each material, phase solubility studies were performed to design the phase solubility diagram. Inclusion complexes from this approach showed a significant increase in solubility [64]. By adopting the complexation through kneading approach, nimesulide dissolution was improved [65]. In one study, a BCS class II medication was identified called azithromycin using physical characterization and melting point determination. Melting, kneading, and solvent evaporation were used to generate azithromycin's solid dispersions. From the study's findings, it can be determined that the melting and kneading approaches successfully increased the solubility of the azithromycin to the maximum compared to the solvent evaporation method [66].

Electrospinning Method.
is technology combines solid dispersion technology with nanotechnology to be used in the polymer industry. is technique exposes a liquid stream of  [67]. e generated fibres can be collected on a screen to make a woven fabric, or they can be gathered on a spinning mandrel as the solvent evaporates. Surface tension, dielectric constant, feeding rate, and electric field strength all influence the fibre diameter. Because it is the simplest and cheapest technology for preparing nanofibers and controlling the release of medicines, it has enormous potential. In the future, this approach could be used to make solid dispersions [16]. e simplicity and low cost of this method make it advantageous. is technique works well for making nanofibers and managing the release of biomedical treatments. By electrospinning, a nanofiber of polyvinyl alcohol (PVA) : ketoprofen (1 : 1, w/w) was created. e dissolution rate of this nanofiber was significantly greater than that of ketoprofen alone (p < 0.05). In a different investigation, indomethacin and griseofulvin were combined in an amorphous form using the electrospinning technique and the PVP was the carrier. For eight months, this mixture remained stable in a desiccator [68].

Solid Dispersion Characterization
In solid dispersions, the medication in the matrix can take on a variety of molecular configurations. e molecular arrangement in solid dispersions has been studied in several ways. However, much work has gone into distinguishing between amorphous and crystalline materials [16]. For this purpose, many approaches exist to detect the amount of crystalline material in the dispersion. e amount of amorphous material in a sample can never be directly measured, but it can be estimated based on the amount of Table 7: Different characterization methods to assess solid dispersion [6].

Characterization
Technique Purpose [69] Drug-carrier interactions Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and solid-state NMR studies Used for studying biological reactions and for the validation of production materials and identification of unknown compounds. It is also used for detecting any new interaction Drug-carrier miscibility Hot-stage microscopy (HSM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) Used for identifying thermal transition and for achieving a threedimensional model

Surface properties
Dynamic vapour sorption, inverse gas chromatography, atomic force microscopy, and Raman microscopy Used for supplying details on particle surface thermodynamic properties, such as surface free energy, acid-base interactions, enthalpy, and entropy. Moreover, it is also used for providing details of the solvent quantity that was absorbed on the sample surface crystalline material present. It should be highlighted that using crystallinity to measure the amount of amorphous drug makes it impossible to distinguish whether the drug is present as amorphous drug particles or as molecularly dispersed molecules. Table 7 summarizes the different methods applied to characterize solid dispersions [6].

Marketed Products Used the Solid Dispersion Approach.
Several drugs are already on the market and have been prepared using the various approaches of solid dispersion [12]. Some of the products are shown in Table 8. Different approaches can perform solid dispersion. As a result, solid dispersion methods have been extensively used to improve the solubility of poorly water-soluble drugs. Table 6 shows the Praziquantel drugs that have been studied using different solid dispersion methods with various carriers.

Solid Dispersion in Polymeric Matrices for In Vitro Studies.
is section covers solid dispersions (SDs) used to improve the characteristics and release of poorly soluble natural and synthetic medicines and drug candidates [78]. e synthesis and usage of SDs have been reported in many in vitro investigations, which have been numerically quantified and categorized in Figure 5 based on the biological activities of   their active compounds, with the major information from this research summarized in Table 9.

In Vivo Studies on Solid Dispersions in Polymeric Matrices.
As previously indicated, solid dispersions (SDs) have been employed in pharmaceutical technology to overcome some of the limits posed by pharmaceuticals and new bioactive substances, such as the limited solubility and bioavailability [78]. In this regard, as seen in Figure 3 and quantitatively quantified in Figure 6, this section discusses in vivo studies on SDs with various biological activities. Table 10 summarizes the most important aspects of this research. In Vivo studies

Drawbacks of Solid Dispersions
ere are several drawbacks that limit the use of solid dispersion in the drug formulation process, including [18] the following: (i) Demanding and costly techniques of preparation (ii) Physicochemical properties reproducibility (iii) Difficulty merging dosage forms into the formulation (iv) Scaling up of the manufacturing process (v) Stability of medications and solvent 6. Conclusion e oral route of medicine administration is the most common and preferred form of delivery due to its simplicity and convenience of oral administration. From the patient's perspective, ingesting medicine is a convenient and accustomed way to take medicines. As a result, oral medication delivery is frequently more efficient in terms of patient compliance and drug therapy than alternate modes of administration, such as parenteral. When taken orally, an active drug must dissolve in the stomach and/or intestinal fluids before it can cross the GI tract's membranes and enter the bloodstream.
As a result, low medication bioavailability is caused by low drug absorption from the gastrointestinal (GI) tract, which is significantly influenced by the drug's molecule's water solubility and membrane permeability. Solid dispersion systems have proven to be a valuable method for increasing the dissolving properties of poorly water-soluble medications. Solid dispersion technology has gained much knowledge in recent years, but its practical use is still limited. Several ways have recently been tried to overcome limitations and make the preparation more realistic. In addition, the issues involved in incorporating dosage forms into formulation have been increasingly resolved with the development of various solutions. Spraying sugar beads and directly filling capsules are two examples. is study has addressed the aim as well as objectives. is research study was performed by using a review design. ere were some major limitations in the study. is research study has no specific methodology section, where the design was specifically described and evidenced. is article has also not talked about any of the processes by which data were collected and the number of articles selected for data collection. ese limitations should be addressed in future research studies.
Although there are significant challenges to solve, such as scale-up and production costs, solid dispersion technology has considerable potential for improving the drug release profile of poorly water-soluble medicines.

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