Drug release from an ensemble of swellable crosslinked polymer particles

Preparation of biocompatibility coating on magnesium alloy surface by sodium alginate and carboxymethyl chitosan hydrogel

Magnesium alloy is an excellent material for biodegradable cerebrovascular stents. However, the rapid degradation rate of magnesium alloy will make stent unstable. To improve the biocompatibility of magnesium alloy, in this study, biodegradable sodium alginate and carboxymethyl chitosan (SA/CMCS) was used to coat onto hydrothermally treated the surface of magnesium alloy by a dipping coating method. The results show that the SA/CMCS coating facilitates the growth, proliferation, and migration of endothelial cells and promotes neovascularization. Moreover, the SA/CMCS coating suppresses macrophage activation while promoting their transformation into M2 type macrophages. Overall, the SA/CMCS coating demonstrates positive effects on the safety and biocompatibility of magnesium alloy after implantation, and provide a promising therapy for the treatment of intracranial atherosclerotic stenosis in the future.

Dissolution of irregularly-shaped drug particles: mathematical modelling

The prediction of drug dissolution profiles is crucial for elucidating the pharmacokinetic behaviour of drugs and the bioavailability of dosage forms. In this work, we develop a mathematical model to describe the dissolution process of irregularly shaped particles. We use a complete dissolution model that accounts for both surface kinetics and convective diffusion. The mechanistic relationship between the mass transfer coefficient and the local curvature is derived from the fundamental physical laws governing these processes. Our model theoretically shows that the dissolution rate depends nonlinearly on the surface curvature. The subsequent recrystallization process in the bulk fluid is also considered. The main result of this work is its simplicity, since only two coupled nonlinear ordinary differential equations are needed to describe the dissolution process. Another remarkable advantage is the possibility to determine the model parameters using common independent techniques, so that the importance of the wettability of solids on the dissolution process can be evaluated. Finally, the proposed model demonstrated the importance of particle shape in describing the experimental dissolution data of theophylline monohydrate.

Computational pharmaceutics - A new paradigm of drug delivery

In recent decades pharmaceutics and drug delivery have become increasingly critical in the pharmaceutical industry due to longer time, higher cost, and less productivity of new molecular entities (NMEs). However, current formulation development still relies on traditional trial-and-error experiments, which are time-consuming, costly, and unpredictable. With the exponential growth of computing capability and algorithms, in recent ten years, a new discipline named "computational pharmaceutics" integrates with big data, artificial intelligence, and multi-scale modeling techniques into pharmaceutics, which offered great potential to shift the paradigm of drug delivery. Computational pharmaceutics can provide multi-scale lenses to pharmaceutical scientists, revealing physical, chemical, mathematical, and data-driven details ranging across pre-formulation studies, formulation screening, in vivo prediction in the human body, and precision medicine in the clinic. The present paper provides a comprehensive and detailed review in all areas of computational pharmaceutics and "Pharma 4.0", including artificial intelligence and machine learning algorithms, molecular modeling, mathematical modeling, process simulation, and physiologically based pharmacokinetic (PBPK) modeling. We not only summarized the theories and progress of these technologies but also discussed the regulatory requirements, current challenges, and future perspectives in the area, such as talent training and a culture change in the future pharmaceutical industry.

Preliminary studies on drug delivery of polymeric primaquine microparticles using the liver high uptake effect based on size of particles to improve malaria treatment

Malaria is the most common parasitic disease around the world, especially in tropical and sub-tropical regions. This parasitic disease can have a rapid and severe evolution. It is transmitted by female anopheline mosquitoes. There is no reliable vaccine or diagnostic test against malaria; instead, Artesunate is used for the treatment of severe malaria and Artemisinin is used for uncomplicated falciparum malaria. However, these treatments are not efficient against severe malaria and improvements are needed. Primaquine (PQ) is one of the most widely used antimalarial drugs. It is the only available drug to date for combating the relapsing form of malaria. Nevertheless, it has severe side effects. Particle drug-delivery systems present the ability to enhance the therapeutic properties of drugs and decrease their side effects. Here, we report the development of Polymeric Primaquine Microparticles (PPM) labeled with 99mTc for therapeutic strategy against malaria infection. The amount of primaquine encapsulated into the PPM was 79.54%. PPM presented a mean size of 929.47 ± 37.72 nm, with a PDI of 0.228 ± 0.05 showing a homogeneous size for the microparticles and a monodispersive behavior. Furthermore, the biodistribution test showed that primaquine microparticles have a high liver accumulation. In vivo experiments using mice show that the PPM treatments resulted in partial efficacy and protection against the development of the parasite compared to free Primaquine. These results suggest that microparticles drug delivery systems of primaquine could be a possible approach for malaria prevention and treatment.

Dissolution of an ensemble of differently shaped poly-dispersed drug particles undergoing solubility reduction: mathematical modelling

The aim of this theoretical paper is to develop a mathematical model for describing the dissolution process, in a finite liquid environment, of an ensemble of poly-dispersed drug particles, in form of sphere, cylinder and parallelepiped that can undergo solubility reduction due to phase transition induced by dissolution. The main result of this work consists in its simplicity as, whatever the particular particles size distribution, only two ordinary differential equations are needed to describe the dissolution process. This, in turn, reflects in a very powerful and agile theoretical tool that can be easily implemented in electronic sheets, a widespread tool among the research community. Another model advantage lies on the possibility of determining its parameters by means of common independent techniques thus enabling the evaluation of the importance of solid wettability on the dissolution process.

Investigation of Dissolution Mechanism and Release Kinetics of Poorly Water-Soluble Tadalafil from Amorphous Solid Dispersions Prepared by Various Methods

The aims of this study were to investigate how the release of tadalafil is influenced by two grades of polyvinylpyrrolidone (Kollidon® 12 PF and Kollidon® VA 64) and various methods of preparing solid dispersions (solvent evaporation, spray drying and hot-melt extrusion). Tadalafil is poorly water-soluble and its high melting point makes it very sensitive to the solid dispersion preparation method. Therefore, the objectives were to make a comparative evaluation among different solid dispersions and to assess the effect of the physicochemical nature of solid dispersions on the drug release profile with respect to the erosion-diffusion mechanism. The solid dispersions were evaluated for dissolution profiles, XRD, SEM, FT-IR, DSC, and solubility or stability studies. It was found that tadalafil release was influenced by polymer molecular weight. Therefore, solid dispersions containing Kollidon® 12 PF showed a faster dissolution rate compared to Kollidon® VA 64. Tadalafil was released from solid dispersions containing Kollidon® 12 PF because of the combination of erosion and diffusion mechanisms. The diffusion mechanisms were predominant in the initial phase of the experiment and the slow erosion was dissolution-controlling at the second stage of the dissolution. On the contrary, the tadalafil release rate from solid dispersions containing Kollidon® VA 64 was controlled solely by the erosion mechanism.

Theoretical Importance of PVP-Alginate Hydrogels Structure on Drug Release Kinetics

BACKGROUND

The new concepts of personalized and precision medicine require the design of more and more refined delivery systems. In this frame, hydrogels can play a very important role as they represent the best surrogate of soft living tissues for what concerns rheological properties. Thus, this paper focusses on a global theoretical approach able to describe how hydrogel polymeric networks can affect the release kinetics of drugs characterized by different sizes. The attention is focused on a case study dealing with an interpenetrated hydrogel made up by alginate and poly(N-vinyl-2-pyrrolidone).

METHODS

Information about polymeric network characteristics (mesh size distribution and polymer volume fraction) is deduced from the theoretical interpretation of the rheological and the low field Nuclear Magnetic Resonance (NMR) characterization of hydrogels. This information is then, embodied in the mass balance equation whose resolution provides the release kinetics.

RESULTS

Our simulations indicate the influence of network characteristics on release kinetics. In addition, the reliability of the proposed approach is supported by the comparison of the model outcome with experimental release data.

CONCLUSIONS

This study underlines the necessity of a global theoretical approach in order to design reliable delivery systems based on hydrogels.

Investigation of the Size Distribution for Diffusion-Controlled Drug Release From Drug Delivery Systems of Various Geometries

Various drug delivery systems (DDSs) are often used in modern medicine to achieve controlled and targeted drug release. Diffusional release of drugs from DDSs is often the main mechanism, especially at early times. Generally, average dimensions of DDS are used to model the drug release, but our recent work on drug release from fibers demonstrated that taking into account diameter distribution is essential. This work systematically investigated the effect of size distribution on diffusional drug release from DDSs of various geometric forms such as membranes, fibers, and spherical particles. The investigation clearly demonstrated that the size distribution has the largest effect on the drug release profiles from spherical particles compared to other geometric forms. Published experimental data for drug release from polymer microparticles and nanoparticles were fitted, and the diffusion coefficients were determined assuming reported radius distributions. Assuming the average radius when fitting the data leads to up to 5 times underestimation of the diffusion coefficient of drug in the polymer.

Characterization of alginate/chitosan-based nanoparticles and mathematical modeling of their SpBMP-9 release inducing neuronal differentiation of human SH-SY5Y cells

The incidence of brain degenerative disease such as Alzheimer's disease (AD) will increase as the world population is ageing. While current AD treatments have only a transient effect, there are many evidences indicating that some growth factors, such as BMP-9, may be used to treat AD. However, growth factors cannot readily access the brain because of their size and the presence of the blood brain barrier. We have therefore developed a small peptide derived from BMP-9, SpBMP-9, which can promote the differentiation of cholinergic neurons and inactivate GSK3beta, a Tau kinase. Here, we investigated the potential of a nanoparticle-based delivery system of SpBMP-9, made of alginate and chitosan (Alg/Chit NPs), as a new therapeutic strategy against AD. The Alg/Chit NPs size distribution revealed NPs with an average diameter of ∼240nm. The encapsulation efficiency of SpBMP-9 was ∼70% of the initial peptide mass loading. Release kinetics of SpBMP-9 were performed in physiological conditions and modelled with a mechanistic framework that took into account the size distribution of Alg/Chit NPs. The release of SpBMP-9 revealed to be mostly diffusive, but there were interactions between the peptide and the alginate chains. The Alg/Chit NPs could also increase the viability of SH-SY5Y cells in comparison to the control. Finally, the SpBMP-9 released from Alg/Chit NPs promoted the SH-SY5Y differentiation into mature neurons as demonstrated by a higher neurite outgrowth and an increased expression of the neuronal markers NSE and VAchT. In conclusion, the nano-scale SpBMP-9 delivery system made of Alg/Chit may be a promising therapeutic strategy against AD.

Mathematical Modeling of Drug Release from Natural Polysaccharides Based Matrices

The new concept of personalized medicine and the affirmation of Nucleic Acid Based Drugs (NABDs), an emerging class of bio-drugs constituted by short sequences of either DNA or RNA, represent a new challenge for the mathematical modelling in the drug delivery and adsorption field. Indeed, whether patient uniqueness asks for the use of theoretical tools enabling a rational approach adapting to each patient, NABDs delivery brings to our attention new aspects of drug delivery due to the NABDs fragile nature and way of action. This review aims to present and discuss the mathematical modelling of drug release from natural polysaccharides matrices with particular care to the description of the chemical and physical phenomena ruling drug delivery.

Mathematical modelling of the drug release from an ensemble of coated pellets

BACKGROUND AND PURPOSE

Coated pellets are widely used as oral drug delivery systems, being highly accepted by patients and with several advantages compared to single unit devices. However, their behaviour needs to be elucidated so as to improve the effectiveness of the formulations and reduce production costs. In spite of this important issue, few mathematical modelling studies have been attempted, mostly due to the complexities arising from the system's polydispersity (non-homogeneous multiple-unit particulate systems), which has been scarcely investigated using mechanistic models.

EXPERIMENTAL APPROACH

A mechanistic mathematical model was developed that was able to describe the single pellet behaviour in terms of hydration, drug dissolution, diffusion and release and particle size. This model was then extended to describe and predict the behaviour of mono- and polydispersed ensembles of pellets.

KEY RESULTS

The polydispersity arising from the size and distribution of the inert core was shown to have a minimal effect on the drug release profile, whereas the thickness and distribution of the polymeric film was found to be the key parameter determining the drug release.

CONCLUSIONS AND IMPLICATIONS

The mechanistic model developed, which is capable of determining the polydispersity of the drug delivery system, was able to predict the release kinetics from ensembles of pellets and to highlight the key parameters that need to be controlled in the production of pellet-based drug delivery systems, demonstrating its use as a powerful predictive tool.

Biosorption of lead, copper and cadmium using the extracellular polysaccharides (EPS) of Bacillus sp., from solar salterns

Extracellular Polysaccharides (EPS) from both prokaryotes and eukaryotes have a great deal of research interest as they protect the producer from different stresses including antibiotics, ionic stress, desiccation and assist in bio-film formation, pathogenesis, adhesion, etc. In this study haloalkaliphilic Bacillus sp., known to cope with osmophilic stress, was selected and screened for EPS production. The EPS were isolated, partially purified and chemical characteristics were documented using liquid FT-IR followed by assessment of heavy metal biosorption (lead, copper and cadmium) using Atomic Absorption Spectroscopy (AAS). The EPS extracted from three isolates B. licheniformis NSPA5, B. cereus NSPA8 and B. subtilis NSPA13 showed maximum biosorption of Lead followed by Copper and Cadmium. Of the tested isolates, the EPS from isolate B. cereus NSPA8 showed maximum (90 %) biosorption of the lead.

Synthesis and in vitro evaluation of melatonin entrapped PLA nanoparticles: an oxidative stress and T-cell response using golden hamster

This study was carried out to evaluate the effects of melatonin entrapped PLA nanoparticles (Mel-NPs) and pure Mel on impact of reactive oxygen species (ROS), blastogenic responses (%SR) in terms of proliferation of splenocytes. ROS have been proposed to play an important role in balancing the pro- and antioxidant homeostasis during different physiological condition of organism. Melatonin has been suggested as an effective free radical scavenger that may have an important role during this process. Mel-NPs were prepared by using emulsification (o/w) nanoprecipitation method and their physicochemical characterizations were studied for evaluation of particle size and encapsulation efficiency by using SEM, TEM, particle size analyzer, DSC and FTIR. The TEM micrograph showed excellent findings regarding size, shape, encapsulation efficiency and difference between pure PLA nanoparticles and Mel-NPs. The SEM micrographs of Mel-NPs showed spherical shape, smooth surfaces and the homogeneous particle size distribution. In TEM micrograph, the average diameter of Mel-NPs was found to be 36 ± 8 nm with ∼78% (w/w) of entrapment efficiency. The size of pure PLA nanoparticles was found to be larger as compared to Mel-NPs which confirm that the drug supports the reduction of the size of Mel-NPs. In in vitro study, we observed that Mel-NPs significantly reduce the level of ROS in splenocytes and increased the level %SR at 96 h of splenocytes culture as compared to the culture with pure Mel. Thus our results propose high clinical value for improvement of depressed immunity by Mel-NPs.

Application of mathematical modeling in sustained release delivery systems

INTRODUCTION

This review, presenting as starting point the concept of the mathematical modeling, is aimed at the physical and mathematical description of the most important mechanisms regulating drug delivery from matrix systems. The precise knowledge of the delivery mechanisms allows us to set up powerful mathematical models which, in turn, are essential for the design and optimization of appropriate drug delivery systems.

AREAS COVERED

The fundamental mechanisms for drug delivery from matrices are represented by drug diffusion, matrix swelling, matrix erosion, drug dissolution with possible recrystallization (e.g., as in the case of amorphous and nanocrystalline drugs), initial drug distribution inside the matrix, matrix geometry, matrix size distribution (in the case of spherical matrices of different diameter) and osmotic pressure. Depending on matrix characteristics, the above-reported variables may play a different role in drug delivery; thus the mathematical model needs to be built solely on the most relevant mechanisms of the particular matrix considered.

EXPERT OPINION

Despite the somewhat diffident behavior of the industrial world, in the light of the most recent findings, we believe that mathematical modeling may have a tremendous potential impact in the pharmaceutical field. We do believe that mathematical modeling will be more and more important in the future especially in the light of the rapid advent of personalized medicine, a novel therapeutic approach intended to treat each single patient instead of the 'average' patient.

Tandem ATRP/Diels–Alder synthesis of polyHEMA-based hydrogels

An efficient controlled process for the preparation of HEMA-based hydrogels by means of the Diels–Alder reaction.

Physiologic and metabolic characterization of a new marine isolate (BM39) of Pantoea sp. producing high levels of exopolysaccharide

Background

Marine environments are the widest fonts of biodiversity representing a resource of both unexploited or unknown microorganisms and new substances having potential applications. Among microbial products, exopolysaccharides (EPS) have many physiological functions and practical applications. Since EPS production by many bacteria is too scarce for practical use and only few species are known for their high levels of production, the search of new high EPS producers is of paramount importance. Many marine bacteria, that produce EPS to cope with strong environmental stress, could be potentially exploited at the industrial level.

Results

A novel bacterium, strain BM39, previously isolated from sediments collected in the Tyrrhenian Sea, was selected for its production of very high levels of EPS. BM39 was affiliated to Pantoea sp. (Enterobacteriaceae) by 16S rRNA gene sequencing and biochemical tests. According to the phylogenetic tree, this strain, being quite far from the closest known Pantoea species (96% identity with P. agglomerans and P. ananatis) could belong to a new species. EPS production was fast (maximum of ca. 21 g/L in 24 h on glucose medium) and mainly obtained during the exponential growth. Preliminary characterization, carried out by thin layer and gel filtration chromatography, showed that the EPS, being a glucose homopolymer with MW of ca. 830 kDa, appeared to be different from those of other bacteria of same genus. The bacterium showed a typical slightly halophilic behavior growing optimally at NaCl 40 ‰ (growing range 0-100 ‰). Flow cytometry studies indicated that good cell survival was maintained for 24 h at 120 ‰. Survival decreased dramatically with the increase of salinity being only 1 h at 280 ‰. The biochemical characterization, carried out with the Biolog system, showed that MB39 had a rather limited metabolic capacity. Its ability, rather lower than that of P. agglomerans, was almost only confined to the metabolization of simple sugars and their derivatives. Few alcohols, organic acids and nitrogen compounds were partially used too.

Conclusions

Strain BM39, probably belonging to a new species, due to its remarkable EPS production, comparable to those of known industrial bacterial producers, could be suggested as a new microorganism for industrial applications.

The initial release of cisplatin from poly(lactide-co-glycolide) microspheres

PLGA microspheres loaded with cisplatin were produced using a single emulsion method. A semi-empirical model, with bi-exponential terms, was found to give a better fit to the drug release profiles compared to a mono-exponential model. This model suggests that there are two separate fractions of drug present in the depot. A fraction of the drug is located near/at the surface of the depot, and is readily released during immersion in buffer. A second fraction of drug is entrapped deeper within the depot and is subsequently released. It was also found that the initial release of cisplatin from PLGA microsphere is highly diffusion-controlled and the classical Higuchi model provides a good fit. From studies of water diffusion using PFG-NMR, results suggested that 50:50 PLGA microsphere was most susceptible to swelling and this might have promoted the faster initial drug release. Results from NMR cryoporometry also indicated that the developed PLGA microspheres could have "ink-bottle" pores.

Superficial distribution and identification of antifungal/antimicrobial agents on a modified tissue conditioner by SEM-EDS microanalysis: a preliminary study

PURPOSE

This study evaluated the incorporation pattern of antifungal/antimicrobial agents added to a tissue conditioner by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis.

MATERIALS AND METHODS

The nystatin dosages incorporated into the tissue conditioner (Softone, Bosworth Co., Skokie, IL) powder were 500,000 U (G1) and 1,000,000 U (G2). The addition of miconazole was at 125 mg (G3) and 250 mg (G4), and ketoconazole was at 100 mg (G5) and 200 mg (G6). Chlorhexidine diacetate was blended at levels of 5% (G7) and 10% (G8) w/w of the total amount (6.35 g) of the tissue conditioner. The drug powder concentrations were blended with the tissue conditioner powder at different concentrations before the addition of the tissue conditioner liquid (5 mL) to the mixture. One group (G0) without any drug incorporation was used as control. Specimens (n = 5) (36 x 7 x 6 mm(3)) were plasticized at room temperature for 10 minutes and carbon sputter coated. All specimens were submitted to SEM-EDS analysis.

RESULTS

Nystatin and miconazole specimens exhibited particles with irregular shapes and sizes uniformly distributed. Ketoconazole specimens showed small spherical particles with a slight distribution throughout the matrix. Chlorhexidine specimens exhibited irregular particles up to approximately 50 mum in size randomly dispersed within the matrix.

CONCLUSIONS

Within the limitations of this in vitro study, the modified tissue conditioner showed differences in the particle distribution and size of the antifungal/antimicrobial agent added to the plasticized matrix. Further studies would discriminate the most important particle features that may influence the drug leaching from the plasticized matrix.

Current Perspectives of Solubilization: Potential for Improved Bioavailability

This review focuses on the recent techniques of solubilization for the attainment of effective absorption and improved bioavailability. Solubilization may be affected due to cosolvent water interaction or altered crystal structure by cosolvent addition. Micellar solubilization could be affected by both ionic strength and pH. Addition of cosolvents to the surfactant solutions offers only a small advantage because of the decrease in the solubilization capacity of the micelles. Polymorphism is known to influence dissolution and bioavailability of the drugs. Molecular modeling study of cyclodextrin inclusion complexations can predict the inclusion modes, stoichiometry of the complex, and the relative complexing efficiency of cyclodextrins with various drug molecules.

Doxorubicin and beta-lapachone release and interaction with micellar core materials: experiment and modeling

Polymer micelles with two different core-forming blocks, poly(d,l -lactide) (PLA) and poly(epsilon-caprolactone) (PCL), but the same coronal material, poly(ethylene glycol) (PEG), were investigated in this study as nanoscopic drug carriers. The release of two different drugs, doxorubicin (DOX) and beta-lapachone (beta-lap), from PEG(5k)-b-PCL(5k) and PEG(5k)-b-PLA(5k) micelles was studied at pH 5.0 and 7.4. Mathematical solutions of both Higuchi's model and Fickian diffusion equations were utilized to elucidate the differences between the micelle core materials for the two drugs. The neutral and smaller of the two drugs tested, beta-lap, demonstrated faster, pH-independent release, suggesting that no substantial changes occurred in either micelle core at lower pH. In contrast, the release rate of DOX was found to noticeably increase at lower pH with a larger cumulative amount of drug released. Different core materials were shown to have considerable influence on the release kinetics of both drugs: in both cases, the more hydrophobic PCL core showed slower drug release rates compared with the less hydrophobic PLA core.

Multifunctional polyvinylpyrrolidinone-polyacrylic acid copolymer hydrogels for biomedical applications

Copolymers of N-vinylpyrrolidinone and acrylic acid, crosslinked with ethylene glycol dimethacrylate and polyethylene glycol 600 dimethacrylate were prepared by UV-polymerisation. These polymers were analysed for their extractable content by Soxhlet extraction of the samples at 100 degrees C for 72 h. Aspirin and paracetamol were incorporated into the polymer structure at 25 wt.% during the curing process and their presence confirmed by Fourier transform infrared spectroscopy. It was found that the release rate of the drug from the polymer matrix was dependent on intermolecular bonding between the polymer and active agent with aspirin being released slower than paracetamol in all cases. Results showed that paracetamol was completely released after 24h whereas complete release of aspirin took up to 70 h. Finally preliminary in vitro biocompatibility testing was performed for crosslinked polyvinylpyrrolidinone, by determining human hepatoma HepG2 cell viability in the MTT assay and DNA damage in the comet assay following direct contact with various concentrations of polyvinylpyrrolidinone-containing media. Cytotoxicity data suggests a dose-dependent effect for both crosslinkers, with concentrations in the range 0.025-2.5 mg ml(-1) showing a marginal decrease in viability to, at most, 70% that of untreated cells. Again DNA migration in the comet assay following short-term exposure to EGDMA crosslinked hydrogels correlates with MTT data.

Entrapment ability and release profile of corticosteroids from starch-based microparticles

We previously described the synthesis of starch-based microparticles that were shown to be bioactive (when combined with Bioactive Glass 45S5) and noncytotoxic. To further assess their potential for biomedical applications such as controlled release, three corticosteroids with a similar basic structure-dexamethasone (DEX), 16alpha-methylprednisonole (MP), and 16alpha-methylprednisolone acetate (MPA)-were used as models for the entrapment and release of bioactive agents. DEX, MP, and MPA were entrapped into starch-based microparticles at 10% wt/wt of the starch-based polymer and the loading efficiencies, as well as the release profiles, were evaluated. Differences were found for the loading efficiencies of the three corticosteroids, with DEX and MPA being the most successfully loaded (82 and 84%, respectively), followed by MP (51%). These differences might be explained based on the differential distribution of the molecules within the matrix of the microparticles. Furthermore, a differential burst release was observed in the first 24 h for all corticosteroids with DEX and MP being more pronounced (around 25%), whereas only 12% of MPA was released during the same time period. Whereas the water uptake profile can account for this first stage burst release, the subsequent slower release stage was mainly attributed to degradation of the microparticle network. Differences in the release profiles can be explained based on the structure of the molecule, because MPA, a more bulky and hydrophobic molecule, is released at a slower rate compared with DEX and MP. In this work, it is shown that these carriers were able to sustain a controlled release of the entrapped corticosteroids over 30 days, which confirms the potential of these systems to be used as carriers for the delivery of bioactive agents.

Theoretical analysis of drug release into a finite medium from sphere ensembles with various size and concentration distributions

Release kinetics for heterogeneous sphere ensembles with a dissolved drug, i.e., initial drug loading below or equal to the drug solubility in the matrix, in a finite external medium was modeled with consideration of heterogeneity among and within spheres. Numerical solutions were obtained using the finite element method for sphere ensemble with normal or log-normal distribution of particle size or initial drug loading among spheres. Exact series solutions were derived for ensembles with various initial loading distributions within spheres, namely linear, quadratic, sigmoidal and uniform distribution, using their mean or average radii. Simplified solutions retaining only one term of the series for non-uniform distributions and three terms for uniform distribution were suggested because of their good approximation to the exact solution. The results of finite element analysis showed that the release rate of an ensemble decreased with increasing standard deviation of particle size. Using weight-average radii in the exact solution gave a prediction of release profile closer to that from the actual size distribution than using mean radii. The three non-uniform loading patterns within spheres all showed reduced initial burst and release rate, leading to more steady release rates than uniform loading, among which the sigmoidal distribution offered the best near-zero order release. Non-uniform initial loading among spheres seemed to have insignificant influence on the release profiles. The volume ratio of liquid to a sphere ensemble played an important role in release kinetics. The derived analytical solutions are applicable to multiple spheres or a single sphere in a finite medium or in a perfect sink.

Effect of the size of biodegradable microparticles on drug release: experiment and theory

The aim of this study was to investigate the effect of the size of biodegradable microparticles (monolithic dispersions) on the release rate of an incorporated drug in a quantitative way. 5-Fluorouracil-loaded, poly(lactic-co-glycolic acid)-based microparticles were prepared with a solid-in-oil-in-water solvent extraction technique. In vitro drug release from different-sized particle fractions was measured in phosphate buffer pH 7.4. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and size exclusion chromatography (SEC) were used to monitor the degradation behavior of the polymer and morphological changes of the microparticles upon exposure to the release medium. Based on these experimental results, an appropriate mathematical theory was identified and used to get further insight into the underlying physical and chemical processes, which are involved in the control of drug release. Interestingly, the relative as well as the absolute release rate of the drug increased with increasing microparticle radius, despite of the increasing diffusion pathways. SEC, DSC and SEM analysis revealed that the degradation behavior of the matrix forming polymer was not significantly affected by the size of the devices and that autocatalytic effects do not seem to play a major role. Importantly, the initial drug loading significantly increased with increasing radius of the drug delivery system. Thus, large microparticles became more porous during drug release than small microparticles, leading to higher apparent diffusivities and drug transport rates. This effect overcompensated the effect of the increasing diffusion pathways with increasing microparticle radius, resulting in increased drug release rates with increasing device dimension. The applied mathematical model, considering drug diffusion with non-constant diffusivities (to account for polymer degradation) was able to quantitatively describe the observed drug release patterns. Importantly, an exponential relationship could be established between the diffusion coefficient and the initial loading of the drug. Based on this dependency, it was possible to predict the resulting drug release kinetics for arbitrary microparticle sizes in a quantitative way.

In vitro Nimesulide Absorption from Different Formulations

In light of improving the bioavailability of poorly water-soluble drugs, this work focused on the comparison among different nimesulide formulations resorting to in vitro absorption experiments through everted rat intestine. The performance of a nimesulide ethanol-triacetin solution, an activated system made up by cogrinding nimesulide/polyvinylpyrrolidone and simple solid nimesulide were compared with that of a reference nimesulide solution. Although ethanol-triacetin solution showed a better performance than the solid nimesulide because wettability problems connected with nimesulide were completely zeroed, the activated system showed a better performance than the reference solution one. This was due to the fact that the activated system allowed to overcome both the wettability and solubility problems connected with nimesulide. Moreover, as proved by intestinal pictures taken before and after permeation experiments, we observed the adhesion of polymeric particles to intestinal villi, this giving origin to a thin layer, surrounding the intestine, characterized by a nimesulide concentration higher than that in the release environment bulk. A proper mathematical model, based on Fick's second law, was developed to model drug absorption in the case of solution and activated system. In this manner, we could calculate nimesulide permeability through the intestinal wall, and we could better define the nature of the above-mentioned thin layer surrounding the intestine. Finally, the mathematical model was used to verify the theoretical correctness of the widely employed technique consisting in data correction for dilution when sample withdrawal and replacement were needed to measure drug concentration in the receiver environment.

Theoretical and experimental study on theophylline release from stearic acid cylindrical delivery systems

The purpose of this study is to evaluate the possibility of developing a cylindrical sustained-release dosage form for theophylline directly by means of a ram extrusion process. In particular, the formulations contained: stearic acid as a low melting binder, monohydrate lactose and polyethylene glycol 6000 as hydrophilic fillers. The influence of type and percentage of the components was studied considering different parameters such as the time required for 50% of the drug release (t50%)and the drug diffusion coefficient in the delivery system. The choice of the different formulations to be tested is carried out employing an axial design with constraint domains. The limits of each component were fixed on the basis of preliminary trials. The analysis of the t50% values revealed that the release kinetics is mainly affected by stearic acid and theophylline content, whilst lactose effect is almost negligible. A substantial correspondence between the experimental results and the analysis of the drug release kinetics performed by means of an ad hoc developed mathematical model was found. The proposed mathematical model allows to conclude that wherever the release mechanism is initially ruled by dissolution, then diffusion plays the most important role.

Characterization of a quaternary liquid system improving the bioavailability of poorly water soluble drugs

The aim of this work is the characterization of the quaternary system composed of water, triacetin (oil), ethanol (alcohol), and Tween 80 (surfactant), as its results enable the enhancement of the bioavailability of nimesulide, a poorly water soluble nonsteroidal antiinflammatory drug widely employed in the pharmaceutical field. Particular attention is devoted to the surfactant-free ternary system, as it proved able to solubilize nimesulide as well, and the absence of a surfactant is desirable in order to keep the preparation as tolerable as possible. Both bulk and interfacial properties of this system are investigated, and a mathematical model to calculate the interface composition of a three-component two-phase system is developed. This model is based on Gibbs' theory on interfaces, which considers an arbitrary mathematical dividing surface so that the two phases continue uniformly up to it, although interface regions have no sharply defined boundaries. We find that both the quaternary and the ternary systems investigated show a miscibility lacuna and that, in the surfactant-free ternary system, an increase of the ethanol weight fraction is reflected as an impoverishment of the ethanol interfacial molar fraction.