Preparation in high-shear mixer of sustained-release pellets by melt pelletisation

Question-based review for pharmaceutical development: An enhanced quality approach

Over the last years, the pharmaceutical industry has faced real challenges regarding quality assurance. In this context, the establishment of more holistic approaches to the pharmaceutical development has been encouraged. The emergence of the Quality by Design (QbD) paradigm as systematic, scientific and risk-based methodology introduced a new concept of pharmaceutical quality. In essence, QbD can be interpreted as a strategy to maximize time and cost savings. An in-depth understanding of the formulation and manufacturing process is demanded to optimize the safety, efficacy and quality of a drug product at all stages of development. This innovative approach streamlines the pharmaceutical Research and Development (R&D) process, provides greater manufacturing flexibility and reduces regulatory burden. To assist in QbD implementation, International Conference on Harmonisation (ICH), U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) organized and launched QbD principles in their guidance for industry, identifying key concepts and tools to design and develop a high-quality drug product. Despite the undeniable advantages of the QbD approach, and the widespread information on QbD regulatory expectations, its full implementation in the pharmaceutical field is still limited. The present review aims to establish a crosswise overview on the current application status of QbD within the framework of the ICH guidelines (ICH Q8(R2) - Q14 and ICH Q2(R2)). Moreover, it outlines the way information gathered from the QbD methodology is being harmonized in Marketing Authorization Applications (MAAs) for European market approval. This work also highlights the challenges that hinder the deployment of the QbD strategy as a standard practice.

Twin-Screw Melt Granulation for Oral Solid Pharmaceutical Products

This article highlights the advantages of pharmaceutical continuous melt granulation by twin-screw extrusion. The different melt granulation process options and excipients are described and compared, and a case is made for expanded use of twin-screw melt granulation since it is a flexible and continuous process. Methods for binder selection are profiled with a focus on rheology and physical stability impacts. For twin-screw melt granulation, the mechanism of granulation and process impact on granule properties are described. Pharmaceutical applications of melt granulation ranging from immediate release of soluble and insoluble APIs, taste-masking, and sustained release formulation are reviewed, demonstrating the range of possibilities afforded by twin-screw melt granulation.

Prilling of API/fatty acid suspensions: Processability and characterisation

Current study evaluated the processability and characteristics of prills made of an active pharmaceutical ingredient/fatty acid (API/FA) suspension instead of previously studied API/FA solutions to enlarge the application field of prilling. Metformin hydrochloride (MET) and paracetamol (PAR) were used as model APIs while both the effect of drug load (10-40%) and FA chain length (C14-C22) were evaluated. API/FA suspensions were processable on lab-scale prilling equipment without thermal degradation, nozzle obstruction or sedimentation in function of processing time. The collected prills were spherical (AR ≥ 0.898) with a smooth surface (sphericity ≥ 0.914) and a particle size of ±2.3 mm and 2.4 mm for MET and PAR prills, respectively, independent of drug load and/or FA chain length. In vitro drug release evaluation revealed a faster drug release at higher drug load, higher API water solubility and shorter FA chain length. Solid state characterisation via XRD and Raman spectroscopy showed that API and FA crystallinity was maintained after thermal processing via prilling and during storage. Evaluation of the similarity factor indicated a stable drug release (f₂ > 50) from MET and PAR prills after 6 months storage at 25 °C or 40 °C.

Exploring mechanochemical parameters using a DoE approach: Crystal structure solution from synchrotron XRPD and characterization of a new praziquantel polymorph

A rotated Doehlert matrix was utilized to explore the experimental design space around the milling parameters of Praziquantel (PZQ) polymorph B formation in terms of frequency and milling time. Three experimental responses were evaluated on the resulting ground samples: two quantitative responses, i.e. median particle size by Laser Light scattering (LLS) and drug recovery by HPLC, and one qualitative dependent variable, i.e. the obtained PZQ crystalline form, characterized through X-Ray Powder Diffraction (XRPD) and confirmed by Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA). Temperature inside the jars was kept under constant control during the milling process by using temperature sensor equipped jars (thermojars), thus allowing evaluation of the obtained solid states at each experimental point, considering the specific temperature of the process. This explorative analysis led to the finding of a novel PZQ polymorph, named "Form C", produced without degradation, then fully characterized, including by means of Synchrotron XRPD, Polarimetric, FT-IR, SS-NMR, ESEM and saturation solubility. Crystal structure was solved from XRPD data and its geometry was optimized by DFT calculations (CASTEP). Finally, Form C and Form A activity against adult schistosoma mansoni were compared through in vitro testing, and Form C's physical stability checked. The new polymorph, crystallizing in space group I2/c, physically stable for approximately 2 months, showed a m.p. of 106.84 °C and displayed excellent biopharmaceutical properties (water solubility of 382.69±9.26 mg/l), while preserving excellent activity levels against adult schistosoma mansoni.

Controlled-Release Fine Particles Prepared by Melt Adsorption for Orally Disintegrating Tablets

Melt adsorption is a manufacturing method that offers precise control of particle size distribution of granules and circumvents the disadvantages of conventional melt granulation. However, drug release from particles adsorbed with hydrophobic materials has not been fully investigated, and there are missing details as to whether particles manufactured by this technique can be applied to orally disintegrating tablets (ODT). In this report, we aimed to optimize process parameters and formulation to manufacture ODT containing melt adsorption-particles with the specific characteristic of sustained release. Melt adsorption particles containing Neusilin US2 as the adsorbent were prepared by using various waxes to determine the most suitable material for controlled release formulation. Glycerol fatty acid ester (Poem TR-FB: TR-FB) was the optimal wax examined because of its drug release pattern and tabletability. We then optimized manufacturing conditions by examining granulation time, disintegrant amount per tablet and compression force on the tablet for ODT that meet the criteria of controlled drug release, tensile strength and disintegration of the tablet. Multiple regression analysis revealed the effect of process parameters on tablet properties and drug release with increasing the granulation time affording sustained release of the drug. The analysis also showed that a high compression force crushed the granules coated by TR-FB, which impaired sustained drug release. From the regression model the optimal manufacturing conditions were determined, and the tablet prepared under these conditions concurred with the predicted values and met all criteria. This new technique should contribute to the development of ODT to improve medication adherence.

Melt Adsorption as a Manufacturing Method for Fine Particles of Wax Matrices without Any Agglomerates

We have focused on melt adsorption as manufacture method of wax matrices to control particles size of granules more easily than melt granulation. The purpose of present study was to investigate the possibility of identifying a hydrophobic material with a low melting point, currently used as a meltable binder of melt granulation, to apply as a novel carrier in melt adsorption. Glyceryl monostearate (GM) and stearic acid (SA) were selected as candidate hydrophobic materials with low melting points. Neusilin US2 (US2), with a particle diameter of around 100 µm was selected as a surface adsorbent, while dibasic calcium phosphate dihydrate (DCPD), was used as a non-adsorbent control to prepare melting granules as a standard for comparison. We prepared granules containing ibuprofen (IBU) by melt adsorption or melt granulation and evaluated the particle size, physical properties and crystallinity of granules. Compared with melt granulation using DCPD, melt adsorption can be performed over a wide range of 14 to 70% for the ratio of molten components. Moreover, the particle size; d50 of obtained granules was 100-200 µm, and these physical properties showed good flowability and roundness. The process of melt adsorption did not affect the crystalline form of IBU. Therefore, the present study has demonstrated for the first time that melt adsorption using a hydrophobic material, GM or SA, has the potential capability to control the particle size of granules and offers the possibility of application as a novel controlled release technique.

Solvent-free melting techniques for the preparation of lipid-based solid oral formulations

Lipid excipients are applied for numerous purposes such as taste masking, controlled release, improvement of swallowability and moisture protection. Several melting techniques have evolved in the last decades. Common examples are melt coating, melt granulation and melt extrusion. The required equipment ranges from ordinary glass beakers for lab scale up to large machines such as fluid bed coaters, spray dryers or extruders. This allows for upscaling to pilot or production scale. Solvent free melt processing provides a cost-effective, time-saving and eco-friendly method for the food and pharmaceutical industries. This review intends to give a critical overview of the published literature on experiences, formulations and challenges and to show possibilities for future developments in this promising field. Moreover, it should serve as a guide for selecting the best excipients and manufacturing techniques for the development of a product with specific properties using solvent free melt processing.

Melt granulation in fluidized bed: a comparative study of spray-on versus in situ procedure

OBJECTIVE

The aim of this study was to investigate the influence of process parameters, binder content and binder addition method on characteristics of the granules obtained by melt granulation (MG) in fluidized bed.

METHODS

Spray-on experiments were performed according to 2(3) full factorial design. The effect of binder content, molten binder feed rate, and spray air pressure on granule size and size distribution, granule shape, flowability and drug release rate was investigated. In the in situ experiments, the influence of binder particle size and binder content was evaluated. Solid-state characterization was performed by means of differential scanning calorimetry, X-ray powder diffraction and Fourier transform infrared spectroscopy.

RESULTS

Size of the granules obtained by spray-on procedure was significantly influenced by binder content and spray air pressure, while the width of particle size distribution was mainly affected by binder feed rate. Spray air pressure showed the most significant influence on granule shape. It was shown that smooth and spherical particles with good flow properties may be obtained by both procedures, spray-on and in situ MG. The results obtained indicated the influence of agglomeration mechanism on granule sphericity, with higher degree of granule sphericity observed when immersion and layering was the dominant mechanism. Paracetamol release from granulates was very rapid, but after compression of the granules into tablets, drug release was considerably slower. Solid-state analysis confirmed that the physical form of the granulate components remained unaffected after the MG process.

CONCLUSION

The results presented indicate that MG in fluidized bed could be a good alternative to conventional granulation techniques.

Preparation of lipid aspirin sustained-release pellets by solvent-free extrusion/spheronization and an investigation of their stability

A novel solvent-free extrusion/spheronization technique was investigated for preparing stable aspirin sustained-release pellets. Lipids as binders and the matrix in this technique were extruded below their melting points, and spheronized in a thermomechanical process. Four types of lipids (adeps solidus, Compritol(®) 888 ATO, Precirol(®) ATO5 and Compritol(®) HD5 ATO) and their admixture in different ratios were used to obtain spherical and extended-release pellets. Pellets containing 80% aspirin, 15% adeps solidus and 5% Compritol(®) 888 ATO had the best spherical geometry and met the dissolution requirements of aspirin extended-release tablets in USP 31. Storage stability studies showed that the content of free salicylic acid increased sharply in the traditional pellets produced by wet extrusion/spheronization, from 1.91 to 7.84%, whereas there was little increase in the lipid pellets (from 0.48 to 1.08%). The dissolution rate from the optimal pellets (F11) stored at 26°C did not change, but became faster at 40°C/RH75% after 5 months. Powder X-ray diffraction, scanning electron microscopy (SEM) and differential scanning calorimetry were used to investigate the physical properties of the pellets during stability testing. The increase in the rate of drug release from aged pellets (40°C/RH75%) may result from the partially melted adeps solidus observed in SEM photographs. This study suggests that it is possible to prepare sustained-release pellets by solvent-free extrusion/spheronization using an appropriate mixture of lipids with high stability. In particular, this novel technique is excellent for hygroscopic drugs.

Melt extruded helical waxy matrices as a new sustained drug delivery system

The aim of this research was to prepare helical and cylindrical extrudates by melt extrusion and to evaluate their potential as sustained release dosage form. The systems contained theophylline as water-soluble model drug and microcrystalline wax as thermoplastic binder. The temperature suitable to ensure a successful extrusion process of formulations containing the wax in three different percentages was found to be below the melting point of the excipient. After the production of the extrudates in three different helical shapes (having 2, 3 and 4 blades) and a classical cylindrical shape, the systems were studied by means of X-ray powder diffraction and differential scanning calorimetry to check possible variations of the solid state of the drug during the thermal process. The morphology and chemical composition of the surface of the extrudates were examined by Scanning Electron Microscopy/Energy Dispersive X-ray Microanalysis to evaluate the presence of the drug on the surface of the extrudates and to monitor changes on the aspect of the waxy matrix during dissolution. Then, the different systems were analysed from the in vitro dissolution point of view to study the influence of the shape and of the composition on the drug release. An in vivo pilot study on the best performing system (helix with 3 blades) was carried out on five healthy volunteers and monitoring the intestinal transit by X-ray images. The resulting plasma profiles were analysed by means of a suitable pharmacokinetic analysis. Finally, an ad hoc mathematical model was developed to perform an accurate description of the in vitro release and in vivo performance of the 3-blades helical system.

Design of in situ dispersible and calcium cross-linked alginate pellets as intestinal-specific drug carrier by melt pelletization technique

Conventional alginate pellets underwent rapid drug dissolution and loss of multiparticulate characteristics such as aggregation in acidic medium, thereby promoting oral dose dumping. This study aimed to design sustained-release dispersible alginate pellets through rapid in situ matrix dispersion and cross-linking by calcium salts during dissolution. Pellets made of alginate and calcium salts were prepared using a solvent-free melt pelletization technique that prevented reaction between processing materials during agglomeration and allowed such a reaction to occur only in dissolution phase. Drug release was remarkably retarded in acidic medium when pellets were formulated with water-soluble calcium acetate instead of acid-soluble calcium carbonate. Different from calcium salt-free and calcium carbonate-loaded matrices that aggregated or underwent gradual erosion, rapid in situ solvation of calcium acetate in pellets during dissolution resulted in burst of gas bubbles, fast pellet breakup, and dispersion. The dispersed fragments, though exhibiting a larger specific surface area for drug dissolution than intact matrix, were rapidly cross-linked by Ca(2+) from calcium acetate and had drug release retarded till a change in medium pH from 1.2 to 6.8. Being dispersible and pH-dependent in drug dissolution, these pellets are useful as multiparticulate intestinal-specific drug carrier without exhibiting dose dumping tendency of a "single-unit-like" system via pellet aggregation.

Formulation of ketotifen fumarate fast-melt granulation sublingual tablet

The purpose of this study was to prepare sublingual tablets, containing the antiasthmatic drug ketotifen fumarate which suffers an extensive first-pass effect, using the fast-melt granulation technique. The powder mixtures containing the drug were agglomerated using a blend of polyethylene glycol 400 and 6000 as meltable hydrophilic binders. Granular mannitol or granular mannitol/sucrose mixture were used as fillers. A mechanical mixer was used to prepare the granules at 40 degrees C. The method involved no water or organic solvents, which are used in conventional granulation, and hence no drying step was included, which saved time. Twelve formulations were prepared and characterized using official and non official tests. Three formulations showed the best results and were subjected to an ex vivo permeation study using excised chicken cheek pouches. The formulation F4I possessed the highest permeation coefficient due to the presence of the permeation enhancer (polyethylene glycol) in an amount which allowed maximum drug permeation, and was subjected to a pharmacokinetic study using rabbits as an animal model. The bioavailability of F4I was significantly higher than that of a commercially available dosage form (Zaditen solution-Novartis Pharma-Egypt) (p > 0.05). Thus, fast-melt granulation allowed for rapid tablet disintegration and an enhanced permeation of the drug through the sublingual mucosa, resulting in increased bioavailabililty.

Preparation of sustained release matrix pellets by melt agglomeration in the fluidized bed: influence of formulation variables and modelling of agglomerate growth

The one-step preparation of sustained release matrix pellets, using a melting procedure in a fluidized bed apparatus, was tested in a 2(3) full factorial design of experiments, using microcrystalline wax as lipophilic binder, theophylline as model drug and talc as additional matrix forming agent. The three influence parameters were (A) size of binder particles, (B) fraction of theophylline in solid particles and (C) fraction of microcrystalline wax in formulation. The response variables were agglomerate size and size distribution, dissolution time, agglomerate crush resistance, sphericity, yield and porosity. Nearly spherical pellets comprising a smooth, closed surface could be obtained with the used method, exhibiting the hollow core typical for the immersion and layering mechanism. The reproducibility was very good concerning all responses. The size of agglomerates is proportional to the size of the binder particles, which serve as cores for pellet formation in the molten state in the fluidized bed. Additionally, the agglomerate size is influenced by the volume of the solid particles in relation to the binder particles, with more solid particles leading to larger agglomerates and vice versa. Dissolution times vary in a very wide range, resulting from the interplay between amount of drug in relation to the meltable matrix substance microcrystalline wax and the non-meltable matrix substance talc. The change of binder particle size does not lead to a structural change of the matrix; both dissolution times and porosity are not significantly altered. Agglomerate crush resistance is low due to the hollow core of the pellets. However, it is significantly increased if the volume fraction of microcrystalline wax in the matrix is high, which means that the matrix is mechanically better stabilized. A theoretical model has been established to quantitatively explain agglomerate growth and very good accordance of the full particle size distributions between predicted and actual values could be shown. A low volumetric binder to solids ratio is compensated by a more porous layer. On the basis of this model, in-depth understanding on the mechanism and influence of product properties could be gained; and an a priori estimation of particle size distributions for new formulas can be performed, with densities, formula, and binder particle size distribution as input parameters.

Production variables affecting characteristics of pellets in melt pelletization with wax combination in a laboratory scale spheronizer

The purpose of the study was to evaluate the suitability of laboratory scale spheronizer for the production of spherical pellets loaded with diltiazem hydrochloride by wax combination. The 1:1 combination of cetyl alcohol and hydrogenated castor oil, as low and high melting point waxes, were used. The various production variables affecting the different characteristics of pellets and the process efficiency were evaluated. Drug loaded pellets were evaluated for drug release in distilled water. Bowl temperature primarily affects the sphericity and adhesion of pellets to the bowl. Mass temperature has a pronounced effect on size, size distribution and sphericity of pellets. Wax concentration affects all characteristics of pellets but adhesion was least affected. The effect of these three variables can be compensated by optimizing the friction plate speed. It has been found that the highest yield of pellets (850--1400 microm) with maximum sphericity can be produced by using 45 degrees C bowl temperature, 52 degrees C mass temperature and 1400 rpm friction plate speed.

Effect of Formulation and Processing Variables on the Granulation Kinetics of Hot Melt Granulation (HMG) Process

The objective of the study was to evaluate the effect of formulation factors, such as type of drug and particulate properties of a drug, and processing variables, i.e. jacket temperature, impeller speed, and scale, on granulation kinetics the of hot-melt granulation (HMG) process. Two model active pharmaceutical ingredients (API) Ro-A and indomethacin were selected for this evaluation using poloxamer 188 as a meltable binder. The effect of solid-state properties of API was investigated for Ro-A, whereas the binder properties were maintained constant. General factorial design was used to investigate the effect of independent process variables, impeller speed and jacket temperature using impeller motor power consumption as response variable. Consistent granulation could be developed for Ro-A by optimizing the binder level and impeller speed, however, the addition of third excipient was necessary for indomethacin. The granulation rate was related to the bulk density and the surface area of the drug. The jacket temperature affected overall granulation time but had no significant effect on the granulation kinetics, suggesting that faster heating rate is desirable for optimal productivity. A significant increase in the granulation rate was observed with increase in impeller speed. The effect of impeller speed was further confirmed at 5 L and 25 L scale. From the formulation prospective, the critical factors were the level of binder, inherent binding properties of the API, the solid-state properties of API and binder. From processing perspectives, the impeller speed had a significant effect on the granulation kinetics.

Impact of a non-meltable additive on melt agglomeration with a hydrophobic meltable binder in high-shear mixer

The present study aims to investigate the behavior of melt agglomeration with a low-viscosity hydrophobic meltable binder by using a non-meltable additive. The size, crushing strength, and pore size distribution of resultant agglomerates, the rheological, surface tension, and wetting properties of the molten binder, as well as, the flow characteristics of preagglomeration powder blend were determined. The use of additive showed contradictory agglomerate growth-promoting and -retarding effects on the molten binder surface tension and the interparticulate frictional forces. Critical concentration effects of additive corresponded to threshold transition of agglomeration-promoting to -retarding behavior were discussed.

Oral lipid-based formulations

Poor drug solubility remains a significant and frequently encountered problem for pharmaceutical scientists. The ability of lipid-based formulations to facilitate gastrointestinal absorption of many poorly soluble drug candidates has been thoroughly documented in the published literature. However, a considerable gap exists between our knowledge of this technology and the know-how required for its application. This commentary provides a comprehensive summary of the development, characterization, and utilization of oral lipid-based formulations, from both physicochemical and biopharmaceutical perspectives. The characteristics of currently available lipid excipients are reviewed in context of their application to the basic lipid-based formulation modalities. The fundamental concepts of in vitro and in vivo evaluation of lipid-based formulations are summarized followed by a forward-looking summary of unrealized opportunities and potential limitations to more widespread use of this technology.

Development and optimization of solid dispersion containing pellets of itraconazole prepared by high shear pelletization

This study investigated the solid dispersion containing pellets of itraconazole for enhanced drug dissolution rate. The influence of process parameters used during high shear pelletization on the pellet properties including pellet size and dissolution rate was also studied. Solid dispersions of itraconazole were prepared with Eudragit E100, a hydrophilic polymer, by a simple fusion method followed by powdered and characterized by differential scanning calorimetry and X-ray powder diffraction. Solid dispersions containing pellets were consequently prepared using a lab-scale high shear mixer. In order to improve the product quality, a central composite design was applied to optimize the critical process variables, such as impeller speed and kneading time, and the results were modeled statistically. Itraconazole was presented as an amorphous state in the solid dispersion prepared at a drug to polymer ratio of 1:2. Both studied parameters had great effect on the responses. Powdered solid dispersion and pellets prepared using the optimal parameter settings showed approximately 30- and 70-fold increases in dissolution rate over the pure drug, respectively. Solid dispersion prepared by simple fusion method could be an option for itraconazole solubility enhancement. Pelletization process in high shear mixer can be optimized effectively by central composite design.

Physicochemical characterization of papain entrapped in ionotropically cross-linked kappa-carrageenan gel beads for stability improvement using Doehlert shell design

This work examines the influence of various process parameters on papain entrapped in cross-linked kappa-carrageenan beads for improvement of its stability. A Doehlert shell design (DSD) was employed to investigate the effect of three process variables, namely kappa-carrageenan concentration, KCl concentration, and hardening time, on the entrapment, time required for 50% enzyme release (T50), time required for 90% enzyme release (T90), and particle size. The beads were prepared by dropping the kappa-carrageenan containing papain into a magnetically stirred KCl solution. Topographical characterization was carried out by scanning electron microscopy and entrapment was confirmed by Fourier transform infrared spectroscopy and differential scanning calorimetry. Stability testing was carried out according to the International Conference on Harmonization (ICH) guidelines for zone III and IV. A polymeric matrix was prepared with kappa-carrageenan (3.5% w/v) and potassium chloride (0.5 M) using the ionotropic gelation method, with a hardening time of 20 min. Beads characterized by a spherical disc shape with a collapsed center, an absence of aggregates, an entrapment of 82.75%, a T90 value of 55.36 min, and a composite index of 88.55 were produced. The shelf-life of the enzyme-loaded beads was found to increase to 3.63 years compared with 1.01 years for the conventional formulation. It can be inferred that the proposed methodology can be used to prepare papain-loaded kappa-carrageenan beads for stability improvement.

Effect of a melt agglomeration process on agglomerates containing solid dispersions

The purpose was to produce solid dispersions of a poorly water-soluble drug, Lu-X, by melt agglomeration in a laboratory scale rotary processor. The effect of binder type and method of manufacturing on the dissolution profile of Lu-X was investigated. Lactose monohydrate and Lu-X were melt agglomerated with Rylo MG12, Gelucire 50/13, PEG 3000, or poloxamer 188. Either a mixture of binder, drug, and excipient was heated to a temperature above the melting point of the binder (melt-in procedure) or a dispersion of drug in molten binder was sprayed on the heated excipient (spray-on procedure). The agglomerates were characterized by DSC, XRPD, SEM, and EDX-SEM. The study showed that the agglomerates containing solid dispersions had improved dissolution rates compared to physical mixtures and pure drug. The melt-in procedure gave a higher dissolution rate than the spray-on procedure with PEG 3000, poloxamer 188, and Gelucire 50/13, whereas the opposite was found with Rylo MG12. This was explained by differences in mechanisms of agglomerate formation and growth, which were dominated by immersion with PEG 3000, poloxamer 188, and Gelucire 50/13, and by distribution and coalescence with Rylo MG12. The spray-on procedure resulted in a higher content of Lu-X in the core of the agglomerates when immersion was the dominating mechanism, and in a higher content in the agglomerate surface when distribution was dominating. The melt-in procedure resulted generally in a homogeneous distribution of Lu-X in the agglomerates. The compounds in the agglomerates were found primarily to be crystalline, and the dissolution profiles were unchanged after 12 weeks storage at 25 degrees C at 50% RH.

Solid lipid microparticles: formulation, preparation, characterisation, drug release and applications

This review details the properties of solid lipid microparticles (SLMs): a promising drug carrier system that has been until now rather unexploited. First, the advantages of SLMs compared with other drug carrier systems are listed. Then an overview of SLM manufacturing compounds and techniques is presented. A detailed discussion of the characteristics of SLMs follows, and includes the determination of particle size distribution, the determination of SLM morphology, the solid-state analysis, the determination of SLM drug loading and the factors influencing it. The in vitro drug release studies that have been carried out so far and the parameters affecting them are also described. Some preliminary in vivo aspects (in vivo drug release studies, biocompatibility studies and in vivo fate) are also considered.

Iron(II) sulfate release from drop-formed lipophilic matrices developed by special hot-melt technology

Iron(II) sulfate-containing lipophilic matrices were developed by a special hot-melt technology (melt solidification in drops), using stearin, white wax and their mixture as conventional bed materials. The special technology resulted in spherical particles which can be filled directly into capsules; these store iron as a depot and ensure a slow and uniform release, whereby the irritation of the gastric mucosa by the iron can be decreased. The rates of dissolution of the iron(II) sulfate from the various lipophilic matrices were different, but fundamentally low. Kinetic calculations demonstrated that the rate of dissolution of the iron(II) sulfate was of approximately zero kinetic order. The results of in vivo experiments on rabbits correlated well with the in vitro data. The plasma curves for the animals treated with the iron(II) sulfate preparations varied with the excipients in the depot products. The properties and ratio of the bed materials influenced the release of the iron(II) sulfate. In all probability, the release of the active agent can be regulated through the use of a melt of stearin and white wax in different ratios. The development products functioned as a sustained-release system and ensured elimination of the irritation of the gastric mucosa. At the same time, the results justified the applicability of the special hot-melt technology in the development of the solid dosage form.

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.

Investigation of melt agglomeration process with a hydrophobic binder in combination with sucrose stearate

The melt agglomeration process of lactose powder with hydrogenated cottonseed oil (HCO) as the hydrophobic meltable binder was investigated by studying the physicochemical properties of molten HCO modified by sucrose stearates S170, S770 and S1570. The size, size distribution, micromeritic and adhesion properties of agglomerates as well as surface tension, contact angle, viscosity and specific volume of molten HCO, with and without sucrose stearates, were examined. The viscosity, specific volume and surface tension of molten HCO were found to be modified to varying extents by sucrose stearates which are available in different HLB values and melt properties. The growth of melt agglomerates was promoted predominantly by an increase in viscosity, an increase in specific volume or a decrease in surface tension of the molten binding liquid. The agglomerate growth propensity was higher with an increase in inter-particulate binding strength, agglomerate surface wetness and extent of agglomerate consolidation which enhanced the liquid migration from agglomerate core to periphery leading to an increased surface plasticity for coalescence. The inclusion of high concentrations of completely meltable sucrose stearate S170 greatly induced the growth of agglomerates through increased specific volume and viscosity of the molten binding liquid. On the other hand, the inclusion of incompletely meltable sucrose stearates S770 and S1570 promoted the agglomeration mainly via the reduction in surface tension of the molten binding liquid with declining agglomerate growth propensity at high sucrose stearate concentrations. In addition to being an agglomeration modifier, sucrose stearate demonstrated anti-adherent property in melt agglomeration process. The properties of molten HCO and melt agglomerates were dependent on the type and concentration of sucrose stearate added.

Formulation design of carbamazepine fast-release tablets prepared by melt granulation technique

This work describes a new approach to prepare a fast-release dosage form for carbamazepine (CBZ), involving the use of melt granulation process in high shear mixer for the production of tablets. In particular, the granules containing CBZ were prepared using polyethylene glycol (PEG) 4000 as a melting binder and lactose monohydrate as a hydrophilic filler. The potential of the intragranular addition of crospovidone as a dissolution enhancer and a disintegrant agent was also evaluated. After the analysis of their solid state performed by means of X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC), the granules were characterised from the technological and dissolution point of view. The subsequent step encompassed the preparation and the evaluation of the tablets, including the effect of the extragranular introduction of crospovidone. Besides the remarkable enhancement of drug dissolution rate of the granulates in comparison to physical mixtures and pure drug, no significant differences were found between the dissolution profiles of the granulates containing lactose or crospovidone. However, the difficult disintegration and bad dissolution performance of the tablets not containing intragranular crospovidone highlight the necessity of this disintegrant in the granulating mixture. Moreover, the extragranular addition of a small amount of crospovidone gave rise to a further amelioration of the disintegration and dissolution performances.

Preparation and evaluation of a melt pelletised paracetamol/stearic acid sustained release delivery system

The potential of a sustained release formulation for paracetamol produced by melt pelletisation was investigated. The chosen formulation was based on the combination of stearic acid as a melting binder and anhydrous lactose as a filler. After determination of the size distribution, the pellet characterisation included scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area and true density determination. Hence, the in vitro release from every single size fraction (2000, 1250, 800, 630, <630 microm) was evaluated and the release mechanism was analysed with the help of an appropriate mathematical model. The results of drug content and superficial atomic composition were found to be constant in all pellets size fractions, attesting the ability of melt pelletisation in a high shear mixer to form a product with homogeneous composition. The mathematical model is built on the hypotheses that drug diffusion and solid drug dissolution in the release environment are the key phenomena affecting drug release kinetics. Smaller classes apart (particles are not perfectly spherical), the comparison between model best fitting and experimental data indicated the reasonability of these hypotheses. Moreover, model reliability is proved by its ability of predicting drug release from a known mixture of the above mentioned particles classes.

Controlled release of verapamil hydrochloride from waxy microparticles prepared by spray congealing

In this work, the potential of waxes for preparing with the ultrasonic spray congealing technique microparticles for controlling the in vitro release of verapamil HCl was investigated. The first part of the study encompassed the optimisation of the formulation to achieve an efficient drug incorporation together with a satisfactory in vitro drug release rate. In particular, microcrystalline wax, stearyl alcohol and mixtures of the two were used. Also a surfactant (soya lecithin) was added to the formulations. After the particle size analysis, the characterisation of the microparticles involved the study of the solid state of drug and carriers in the systems (DSC, HSM and XRD) and the morphological and chemical analyses of the microparticle surface (SEM and XPS). Finally, the drug release mechanism from these devices was evaluated using the statistical moment analysis. The results of this study show that by selecting the type and the amount of the carriers, microparticles with a spherical shape and a good encapsulation efficiency were observed. These particles showed a zero-order release for 8 h, without modifying the solid state properties of the drug. Therefore, waxy microparticles prepared by the ultrasonic spray congealing technique are promising solvent-free devices for controlling the release of verapamil HCl.

Development and evaluation of prolonged release pellets obtained by the melt pelletization process

This study was performed in order to evaluate the possibility of obtaining prolonged release matrix pellets by a melt pelletization process in a laboratory high shear mixer (Mi-Pro, Pro-C-epT). Phenylephrine hydrochloride pellet formulations based on lactose 450 mesh and a mixture of Compritol 888 and Precirol ATO 5 as melting binders were evaluated. The fatty binder content of pellets was substantially increased (from 18 to 80% w/w). The effects of jacket temperature, massing time (MT) and impeller speed (IS) on the pellet characteristics were investigated. It was shown that pellets of narrow size distribution can be produced by using an IS of 800 rpm, a chopper speed of 4000 rpm and a MT of 8 min. On the other hand, the applicability of this technique for the production of sustained-release pellets using ciprofloxacin hydrochloride, ketoprofen and theophylline as less water soluble model drugs than phenylephrine hydrochloride was also studied. This study demonstrated that formulations based on an appropriate mixture of Precirol and Compritol can be used to produce in a short time prolonged release pellets for very hydrosoluble drugs like phenylephrine hydrochloride as well as for the other drugs tested.

Preparation and characterisation of ibuprofen-poloxamer 188 granules obtained by melt granulation

The aim of this study was to prepare, by melt granulation, granules containing ibuprofen as a poorly water soluble model drug in order to improve its dissolution rate and its availability; lactose as a diluent and poloxamer 188 (Lutrol F68), as a new meltable hydrophilic binder, were used. The granules were prepared in a laboratory-scale high-shear mixer, using a jacket temperature of 50 degrees C and an impeller speed of 500 rpm. The particle size analysis shows that the main fraction was between 200 and 500 microm, while the determination of drug content indicated that ibuprofen was quite uniformly distributed in all the fractions. Scanning Electron Microscopy (SEM), image and fractal analysis revealed that the granules did not have a perfect spherical shape and a rugged surface (D(s)=2.6475). The in vitro dissolution tests showed an increase in the dissolution rate of granules compared to pure drug and physical mixture. The characterisation of the samples, performed by Differential Scanning Calorimetry (DSC) and X-ray powder diffraction (XRD), suggests that the improvement of dissolution rate could be correlated to the formation of a eutectic mixture between the drug and the binder. Stability studies indicated that the granule properties do not change, at least after 1 year of storage at 25 degrees C. In conclusion, the results of this work suggest that the melt granulation technique is an easy and fast method to improve the dissolution rate of ibuprofen, using poloxamer 188 as a new hydrophilic meltable binder.

Melt agglomeration with polyethylene glycol beads at a low impeller speed in a high shear mixer

This study was performed in order to evaluate the possibility of obtaining spherical agglomerates with a high content of meltable binder by a melt agglomeration process in a high shear mixer. Lactose monohydrate was melt agglomerated with polyethylene glycol (PEG) 1500 or 6000 in a 10-l high shear mixer at an impeller speed of 400 rpm. The PEG 1500 was used as a size fraction of beads, and the PEG 6000 as a fine powder, a powder, unfractionated beads, and size fractions of beads. It was found to be possible to incorporate a high amount of PEG (28% m/m of the amount of lactose), because the rather low impeller speed applied in the present experiments caused less densification of the agglomerates. The fine powder of the PEG 6000 caused a complete adhesion of the mass to the bowl shortly after melting. A rapid agglomerate growth by coalescence was found to be the dominant growth mechanism when agglomeration was performed with the PEG 6000 powder. The PEG beads resulted in a slow and more controllable agglomerate growth, because the growth occurred primarily by an immersion of the lactose particles in the surface of the molten binder droplets. The initial shape of the agglomerates produced with the PEG beads was similar to the spherical shape of the beads. This shape could not be maintained during the process due to a breakage of the agglomerates caused by a hollow structure of the PEG beads.

Melt pelletization in high shear mixer using a hydrophobic melt binder: influence of some apparatus and process variables

The effects of process conditions and the apparatus variables on the granulometric characteristics of a formulation containing a hydrophobic binder (stearic acid), lactose and paracetamol prepared by melt pelletization process were investigated in a 10-litre high shear mixer. The factors under investigation were: impeller speed, massing time, type of impeller blades and presence of the deflector and their reciprocal interactions. Two granule characteristics were analysed: the percentage of aggregates larger than 3000 microm (Y(1)) and the yield of the 2000-microm pellet size fraction (Y(2)). In order to estimate simultaneously the above-mentioned factors, a particular experimental design was adopted, that allowed the reduction of the number of trials from 378 to 35 and took into consideration other uncontrolled factors with the aid of a block variable. Using the postulated model, we found the optimal operating conditions to minimize Y(1) and increase Y(2) by selecting the type of impeller, and by using an impeller speed lower than 300 rpm, a massing time of 8-9 min and by not using the deflector. Finally, the validity of the adopted strategy has been proved with an additional check point.