Inclusion of fenofibrate in a series of mesoporous silicas using microwave irradiation

Investigating the Influence of Processing Conditions on Dissolution and Physical Stability of Solid Dispersions with Fenofibrate and Mesoporous Silica

The study aimed to enhance the solubility of the poorly water-soluble drug, fenofibrate, by loading it onto mesoporous silica, forming amorphous solid dispersions. Solid dispersions with 30% fenofibrate were prepared using the solvent evaporation method with three solvents (ethyl acetate, acetone, and isopropanol) at different temperatures (40 °C, boiling point temperature). Various characteristics, including solid-state properties, particle morphology, and drug release, were evaluated by different methods and compared to a pure drug and a physical mixture of fenofibrate and silica. Results revealed that higher solvent temperatures facilitated complete amorphization and rapid drug release, with solvent choice having a lesser impact. The optimal conditions for preparation were identified as ethyl acetate at boiling point temperature. Solid dispersions with different fenofibrate amounts (20%, 25%, 35%) were prepared under these conditions. All formulations were fully amorphous, and their dissolution profiles were comparable to the formulation with 30% fenofibrate. Stability assessments after 8 weeks at 40 °C and 75% relative humidity indicated that formulations prepared with ethyl acetate and at 40 °C were physically stable. Interestingly, some formulations showed improved dissolution profiles compared to initial tests. In conclusion, mesoporous silica-based solid dispersions effectively improved fenofibrate dissolution and demonstrated good physical stability if prepared under appropriate conditions.

The processes behind drug loading and release in porous drug delivery systems

Porous materials are ubiquitous and exhibit properties suitable for depositing therapeutic compounds. Drug loading in porous materials can protect the drug, control its release rate, and improve its solubility. However, to achieve such outcomes from porous delivery systems, effective incorporation of the drug in the internal porosity of the carrier must be guaranteed. Mechanistic knowledge of the factors influencing drug loading and release from porous carriers allows rational design of formulations by selecting a suitable carrier for each application. Much of this knowledge exists in research areas other than drug delivery. Thus, a comprehensive overview of this topic from the drug delivery aspect is warranted. This review aims to identify the loading processes and carrier characteristics influencing the drug delivery outcome with porous materials. Additionally, the kinetics of drug release from porous materials are elucidated, and the common approaches to mathematical modeling of these processes are outlined.

Unexpected Factors Affecting the Kinetics of Guest Molecule Release from Investigation of Binary Chemical Systems Trapped in a Single Void of Mesoporous Silica Particles

In this work, we present results for loading of well-defined binary systems (cocrystal, solid solution) and untreated materials (physical mixtures) into the voids of MCM-41 mesoporous silica particles employing three different filling methods. The applied techniques belong to the group of "wet methods" (diffusion supported loading - DiSupLo) and "solvent-free methods" (mechanical ball-mill loading - MeLo, thermal solvent free - TSF). As probes for testing the guest1-guest2 interactions inside the MCM-41 pores we employed the benzoic acid (BA), perfluorobenzoic acid (PFBA), and 4-fluorobenzoic acid (4-FBA). The guests intermolecular contacts and phase changes were monitored employing magic angle spinning (MAS) NMR Spectroscopy techniques and powder X-ray diffraction (PXRD). Since mesoporous silica materials are commonly used in drug delivery system research, special attention has been paid to factors affecting guest release kinetics. It has been proven that not only the content and composition of binary systems, but also the loading technique have a strong impact on the rate of guests release. Innovative methods of visualizing differences in release kinetics are presented.

Superiority of Mesoporous Silica-Based Amorphous Formulations over Spray-Dried Solid Dispersions

The aim of this study was to compare the performance of two amorphous formulation strategies: mesoporous silica via solvent impregnation, and solid dispersions by spray drying. Poorly soluble fenofibrate was chosen as the model drug compound. A total of 30% Fenofibrate-loaded mesoporous silica and spray-dried solid dispersions (SDD) were prepared for head-to-head comparisons, including accelerated stability, manufacturability, and in vitro biorelevant dissolution. In the accelerated stability study under 40 °C/75% RH in open dish, mesoporous silica was able to maintain amorphous fenofibrate for up to 3 months based on solid-state characterizations by PXRD and DSC. This result was superior compared to SDD, as recrystallization was observed within 2 weeks. Under the same drug load, fenofibrate-loaded mesoporous silica showed much better flowability than fenofibrate-loaded SDD, which is beneficial for powder handling of the intermediate product during the downstream process. The in vitro 2-stage dissolution results indicated a well-controlled release of fenofibrate from mesoporous silica in the biorelevant media, rather than a burst release followed by fast precipitation due to the recrystallization in the early simulated gastric phase for SDD. The present study demonstrates that mesoporous silica is a promising formulation platform alternative to prevailing spray-dried solid dispersions for oral drug product development.

Recent Advances in Enhancement of Dissolution and Supersaturation of Poorly Water-Soluble Drug in Amorphous Pharmaceutical Solids: A Review

Amorphization is one of the most effective pharmaceutical approaches to enhance the dissolution and oral bioavailability of poorly water-soluble drugs. In recent years, amorphous formulations have been experiencing rapid development both in theoretical and practical application. Based on using different types of stabilizing agents, amorphous formulations can be mainly classified as polymer-based amorphous solid dispersion, coamorphous formulation, mesoporous silica-based amorphous formulation, etc. This paper summarizes recent advances in the dissolution and supersaturation of these amorphous formulations. Moreover, we also highlight the roles of stabilizing agents such as polymers, low molecular weight co-formers, and mesoporous silica. Maintaining supersaturation in solution is a key factor for the enhancement of dissolution profile and oral bioavailability, and thus, the strategies and challenges for maintaining supersaturation are also discussed. With an in-depth understanding of the inherent mechanisms of dissolution behaviors, the design of amorphous pharmaceutical formulations will become more scientific and reasonable, leading to vigorous development of commercial amorphous drug products.

Application of commercially available mesoporous silica for drug dissolution enhancement in oral drug delivery

Due to the high number of poorly water-soluble active pharmaceutical ingredients, oral drug delivery development has become challenging. One of the strategies to enhance drug solubility and to achieve high oral bioavailability is to formulate such compounds into amorphous solid dispersions. In recent years, porous materials have been investigated as possible carriers into which a drug can be adsorbed, such as mesoporous silica, in particular. Unlike the ordered mesoporous network of silica, non-ordered silica already has a "generally regarded as safe" status, and is already used as an excipient in pharmaceutical and cosmetic products. Thus, it is reasonable to expect that products that contain solid dispersions with non-ordered carriers will reach the market sooner and more easily than those with ordered mesoporous carriers. The emphasis of this review is therefore on non-ordered commercially available mesoporous silica and the progress that has been made in development of the use of these materials for improved dissolution rates in oral drug delivery. First, a thorough categorisation of the drug loading methods is presented, followed by discussion on the most important characteristics of solid dispersions (i.e., physical state, stability, drug release). Finally, manufacturability and production of a final solid dosage form are considered.

Drug loading to mesoporous silica carriers by solvent evaporation: A comparative study of amorphization capacity and release kinetics

The sorption of poorly aqueous soluble active pharmaceutical ingredients (API) to mesoporous silica carriers is an increasingly common formulation strategy for dissolution rate enhancement for this challenging group of substances. However, the success of this approach for a particular API depends on an array of factors including the properties of the porous carrier, the loading method, or the attempted mass fraction of the API. At present, there is no established methodology for the rational selection of these parameters. In the present work, we report a systematic comparison of four well-characterised silica carriers and seven APIs loaded by the same solvent evaporation method. In each case, we find the maximum amorphization capacity by x-ray powder diffraction analysis and measure the in vitro drug release kinetics. For a selected case, we also demonstrate the potential for bioavailability enhancement by a permeation essay.

Mesoporous Silica Particles as Drug Delivery Systems-The State of the Art in Loading Methods and the Recent Progress in Analytical Techniques for Monitoring These Processes

Conventional administration of drugs is limited by poor water solubility, low permeability, and mediocre targeting. Safe and effective delivery of drugs and therapeutic agents remains a challenge, especially for complex therapies, such as cancer treatment, pain management, heart failure medication, among several others. Thus, delivery systems designed to improve the pharmacokinetics of loaded molecules, and allowing controlled release and target specific delivery, have received considerable attention in recent years. The last two decades have seen a growing interest among scientists and the pharmaceutical industry in mesoporous silica nanoparticles (MSNs) as drug delivery systems (DDS). This interest is due to the unique physicochemical properties, including high loading capacity, excellent biocompatibility, and easy functionalization. In this review, we discuss the current state of the art related to the preparation of drug-loaded MSNs and their analysis, focusing on the newest advancements, and highlighting the advantages and disadvantages of different methods. Finally, we provide a concise outlook for the remaining challenges in the field.

In-Vitro and In-Vivo Evaluation of Velpatasvir- Loaded Mesoporous Silica Scaffolds. A Prospective Carrier for Drug Bioavailability Enhancement

The limited aqueous solubility of many active pharmaceutical ingredients (APIs) is responsible for their poor performance and low drug levels in blood and at target sites. Various approaches have been adopted to tackle this issue. Most recently, mesoporous silica nanoparticles (MSN) have gained attention of pharmaceutical scientists for bio-imaging, bio-sensing, gene delivery, drug solubility enhancement, and controlled and targeted drug release. Here, we have successfully incorporated the poorly water soluble antiviral drug velpatasvir (VLP) in MSN. These spherical particles were 186 nm in diameter with polydispersity index of 0.244. Blank MSN have specific surface area and pore diameter of 602.5 ± 0.7 m2/g and 5.9 nm, respectively, which reduced after successful incorporation of drug. Drug was in amorphous form in synthesized VLP-loaded silica particles (VLP-MSN) with no significant interaction with carrier. Pure VLP showed poor dissolution with progressive increment in pH of dissolution media which could limit its availability in systemic circulation after oral administration. After VLP loading in silica carriers, drug released rapidly over a wide range of pH values, i.e., 1.2 to 6.8, thus indicating an improvement in the solubility profile of VLP. These particles were biocompatible, with an LD50 of 448 µg/mL, and in-vivo pharmacokinetic results demonstrated that VLP-MSN significantly enhanced the bioavailability as compared to pure drug. The above results clearly demonstrate satisfactory in-vitro performance, biocompatibility, non-toxicity and in-vivo bioavailability enhancement with VLP-MSN.

Myristic Acid Coated Protein Immobilised Mesoporous Silica Particles as pH Induced Oral Delivery System for the Delivery of Biomolecules

Solid core drug delivery systems (SCDDS) were prepared for the oral delivery of biomolecules using mesoporous silica as core, bovine haemoglobin (bHb) as model drug and supercritical fluid (SCF) processing as encapsulation technique. The use of organic solvents or harsh processing conditions in the development of drug delivery systems for biomolecules can be detrimental for the structural integrity of the molecule. Hence, the coating on protein-immobilised particles was performed via supercritical carbon dioxide (scCO₂) processing at a temperature lower than the melting point of myristic acid (MA) to avoid any thermal degradation of bHb. The SCDDS were prepared by bHb immobilisation on mesoporous silica followed by myristic acid (MA) coating at 43 °C and 100 bar in scCO₂. bHb-immobilised silica particles were also coated via solvent evaporation (SE) to compare the protein release with scCO₂ processed formulations. In both cases, MA coating provided required enteric protection and restricted the bHb release for the first two hours in simulated gastric fluid (SGF). The protein release was immediate upon the change of media to simulated intestinal fluid (SIF), reaching 70% within three hours. The release from SCF processed samples was slower than SE formulations, indicating superior surface coverage of MA on particles in comparison to the SE method. Most importantly, the protein conformation remained unchanged after the release from SCDDS as confirmed by circular dichroism. This study clearly demonstrates that the approach involving protein immobilisation on silica and scCO₂ assisted melt-coating method can protect biomolecules from gastric environment and provide the required release of a biologic in intestine without any untoward effects on protein conformation during processing or after release.

Effect of solvent selection on drug loading and amorphisation in mesoporous silica particles

Increasing the dissolution rate of poorly water-soluble active pharmaceutical ingredients (APIs) is a key strategy used for improving their oral bioavailability. One of the formulation approaches is API loading to mesoporous carrier particles, which can increase the dissolution rate through the combination of improved powder wettability and dispersion, higher surface area, and API conversion from crystalline to the amorphous state. From the formulation process point of view, the maximum achievable drug loading is a crucial parameter, which depends on the loading method. Drug loading by sorption from a solution is a technologically attractive approach, since it involves familiar unit operations (mixing, filtration, drying). However, the success of the equilibrium sorption approach depends on the choice of the solvent. In this work we present an experimental study of loading efficiency to mesoporous silica particles, based on a set of 10 APIs combined with 6 different solvents at a range of concentrations. We show that due to the competitive nature of the adsorption process, the solvent with the highest API solubility is not necessarily the best candidate for maximising the API loading. Based on the investigated drug-solvent combinations, we show that the dielectric constant of the solvent is a good predictor of loading efficiency and can be used as a general guideline for solvent selection. On the other hand, we did not find any systematic correlation between commonly measured API properties such as logP and their loading efficiency.

Bioavailability Enhancement of Aripiprazole Via Silicosan Particles: Preparation, Characterization and In vivo Evaluation

The aim of this study was to design a novel carrier for enhancing the bioavailability of the poorly water-soluble drug, aripiprazole (ARP). Silicosan, the applied carrier, was obtained by chemical interaction between tetraethyl orthosilicate (TEOS) and chitosan HCl. Different ARP-loaded silicosan particles were successfully prepared in absence and presence of one of the following surfactants; Tween 80, Poloxamer 407 and cetyltrimethylammonium bromide (CTAB). The prepared ARP-loaded silicosan particles were thoroughly investigated for their structures using FTIR, XRD, and DSC analysis as well as their particle size, zeta potential, flowability, drug content, and in vitro drug release efficiencies. The prepared ARP-loaded silicosan particles were characterized by amorphous structure, high drug entrapment efficiency and a remarkable improvement in the release of aripiprazole in simulated gastric fluid. SEM and EDX revealed that the morphology and silica atom content in the prepared ARP-loaded silicosan particles were affected by the used surfactant in their formulations. The selected ARP-loaded silicosan particles were subjected to in vivo study using rabbits. The obtained pharmacokinetic results showed that the relative bioavailability for orally administered ARP-loaded silicosan particles (SC-2-CTAB) was 66% higher relative to the oral suspension (AUC_0-10h was 16.38 ± 3.21 and 27.23 ± 2.35 ng.h/mL for drug powder and SC-2-CTAB formulation, respectively). The obtained results suggested the unique-structured silicosan particles to be used as successful vehicle for ARP.

Enhancing the dissolution of phenylbutazone using Syloid® based mesoporous silicas for oral equine applications

Three mesoporous silica excipients (Syloid® silicas AL-1 FP, XDP 3050 and XDP 3150) were formulated with a model drug known for its poor aqueous solubility, namely phenylbutazone, in an attempt to enhance the extent and rate of drug dissolution. Although other forms of mesoporous silica have been investigated in previous studies, the effect of inclusion with these specific Syloid® silica based excipients and more interestingly, with phenylbutazone, is unknown. This work reports a significant enhancement for both the extent and rate of drug release for all three forms of Syloid® silica at a 1:1 drug:silica ratio over a period of 30 min. An explanation for this increase was determined to be conversion to the amorphous form and an enhanced drug loading ability within the pores. Differences between the release profiles of the three silicas were concluded to be a consequence of the physicochemical differences between the three forms. Overall, this study confirms that Syloid® silica based excipients can be used to enhance dissolution, and potentially therefore bioavailability, for compounds with poor aqueous solubility such as phenylbutazone. In addition, it has been confirmed that drug release can be carefully tailored based on the choice of Syloid® silica and desired release profile.

Role of Drug Adsorption onto the Silica Surface in Drug Release from Mesoporous Silica Systems

Factors contributing to incomplete drug release from a number of mesoporous silica formulations are not well understood. This study aims to address this gap in knowledge by exploring the role of drug adsorption onto silica substrates during the drug release process in dissolution media. Adsorption isotherms were generated to understand drug adsorption behavior onto the silica surface. Two silica materials were selected (SBA-15 (mesoporous) and Aerosil 200 (nonporous)) to investigate the influence of porous architecture on the adsorption/dissolution processes. The ability of the dissolution medium to wet the silica surface, particularly the porous network, was investigated by the addition of a surfactant to the dissolution medium. The results demonstrated that a larger amount of drug was bound/m² to the nonporous surface than to the mesoporous material. Adsorption isotherms proved useful in understanding drug adsorption/release behavior for the nonporous silica formulation. However, the quantity of drug remaining on the mesoporous silica surface after dissolution was significantly higher than the amount predicted using adsorption isotherm data. These results suggest that a fraction of loaded drug molecules were tightly bound to the silica surface or attached to sites which are inaccessible for the dissolution media. The presence of surfactant, sodium dodecyl sulfate, in the media enhanced drug release from the silica surface. This behavior can be attributed to both the improved wetting characteristics of the media and adsorption of the surfactant to the silica surface. The findings of this study reinforce the significance of the role that silica porous architecture plays in the dissolution process and indicates that accessible surface area is an important parameter to consider for mesoporous systems in relation to drug release.

Mesoporous silica materials: From physico-chemical properties to enhanced dissolution of poorly water-soluble drugs

New approaches in pharmaceutical chemistry have resulted in more complex drug molecules in the quest to achieve higher affinity to their targets. However, these 'highly active' drugs can also suffer from poor water solubility. Hence, poorly water soluble drugs became a major challenge in drug formulation, and this problem is increasing, as currently about 40 of the marketed drugs and 90% of drug candidates are classified as poorly water soluble. Various approaches exist to circumvent poor water solubility and poor dissolution rate in aqueous environment, however, each having disadvantages and certain limitations. Recently, mesoporous silica materials (MSMs) have been proposed to be used as matrices for enhancing the apparent solubility and dissolution rate of different drug molecules. MSMs are ideal candidates for this purpose, as silica is a "generally regarded as safe" (GRAS) material, is biodegradable, and can be readily surface-modified in order to optimize drug loading and subsequent release in the human body. The major advantage of mesoporous silica as drug delivery systems (DDSs) for poorly water soluble drugs lies in their pore size, pore morphology, and versatility in alteration of the surface groups, which can result in optimized interactions between a drug candidate and MSM carrier by modifying the pore surfaces. Furthermore, the drug of interest can be loaded into these pores in a preferably amorphous state, which can increase the drug dissolution properties dramatically. The highlights of this review include a critical discussion about the modification of the physico-chemical properties of MSMs and how these physico-chemical modifications influence the drug loading and the subsequent dissolution of poorly water soluble drugs. It aims to further promote the use of MSMs as alternative strategy to common methods like solubility enhancement by cyclodextrins, micronization, or microemulsion techniques. This review can provide guidance on how to tailor MSMs to achieve optimized drug loading and drug dissolution.

Porous Inorganic Drug Delivery Systems-a Review

Innovative methods and materials have been developed to overcome limitations associated with current drug delivery systems. Significant developments have led to the use of a variety of materials (as excipients) such as inorganic and metallic structures, marking a transition from conventional polymers. Inorganic materials, especially those possessing significant porosity, are emerging as good candidates for the delivery of a range of drugs (antibiotics, anticancer and anti-inflammatories), providing several advantages in formulation and engineering (encapsulation of drug in amorphous form, controlled delivery and improved targeting). This review focuses on key selected developments in porous drug delivery systems. The review provides a short broad overview of porous polymeric materials for drug delivery before focusing on porous inorganic materials (e.g. Santa Barbara Amorphous (SBA) and Mobil Composition of Matter (MCM)) and their utilisation in drug dosage form development. Methods for their preparation and drug loading thereafter are detailed. Several examples of porous inorganic materials, drugs used and outcomes are discussed providing the reader with an understanding of advances in the field and realistic opportunities.

In vitro dissolution models for the prediction of in vivo performance of an oral mesoporous silica formulation

Drug release from mesoporous silica systems has been widely investigated in vitro using USP Type II (paddle) dissolution apparatus. However, it is not clear if the observed enhanced in vitro dissolution can forecast drug bioavailability in vivo. In this study, the ability of different in vitro dissolution models to predict in vivo oral bioavailability in a pig model was examined. The fenofibrate-loaded mesoporous silica formulation was compared directly to a commercial reference product, Lipantil Supra®. Three in vitro dissolution methods were considered; USP Type II (paddle) apparatus, USP Type IV (flow-through cell) apparatus and a USP IV Transfer model (incorporating a SGF to FaSSIF-V2 media transfer). In silico modelling, using a physiologically based pharmacokinetic modelling and simulation software package (Gastroplus™), to generate in vitro/in vivo relationships, was also investigated. The study demonstrates that the in vitro dissolution performance of a mesoporous silica formulation varies depending on the dissolution apparatus utilised and experimental design. The findings show that the USP IV transfer model was the best predictor of in vivo bioavailability. The USP Type II (paddle) apparatus was not effective at forecasting in vivo behaviour. This observation is likely due to hydrodynamic differences between the two apparatus and the ability of the transfer model to better simulate gastrointestinal transit. The transfer model is advantageous in forecasting in vivo behaviour for formulations which promote drug supersaturation and as a result are prone to precipitation to a more energetically favourable, less soluble form. The USP IV transfer model could prove useful in future mesoporous silica formulation development. In silico modelling has the potential to assist in this process. However, further investigation is required to overcome the limitations of the model for solubility enhancing formulations.