Correlation of extrusion forces, raw materials and sphere characteristics

Properties of pellets manufactured by wet extrusion/spheronization process using kappa-carrageenan: effect of process parameters

The aim of this study was to systematically evaluate the pelletization process parameters of kappa-carrageenan-containing formulations. The study dealt with the effect of 4 process parameters--screw speed, number of die holes, friction plate speed, and spheronizer temperature--on the pellet properties of shape, size, size distribution, tensile strength, and drug release. These parameters were varied systematically in a 2(4) full factorial design. In addition, 4 drugs--phenacetin, chloramphenicol, dimenhydrinate, and lidocaine hydrochloride--were investigated under constant process conditions. The most spherical pellets were achieved in a high yield by using a large number of die holes and a high spheronizer speed. There was no relevant influence of the investigated process parameters on the size distribution, mechanical stability, and drug release. The poorly soluble drugs, phenacetin and chloramphenicol, resulted in pellets with adequate shape, size, and tensile strength and a fast drug release. The salts of dimenhydrinate and lidocaine affected pellet shape, mechanical stability, and the drug release properties using an aqueous solution of pH 3 as a granulation liquid. In the case of dimenhydrinate, this was attributed to the ionic interactions with kappa-carrageenan, resulting in a stable matrix during dissolution that did not disintegrate. The effect of lidocaine is comparable to the effect of sodium ions, which suppress the gelling of carrageenan, resulting in pellets with fast disintegration and drug release characteristics. The pellet properties are affected by the process parameters and the active pharmaceutical ingredient used.

Microscopic image analysis techniques for the morphological characterization of pharmaceutical particles: Influence of the software, and the factor algorithms used in the shape factor estimation

The present report highlights the difficulties of particle shape characterizations of multiparticulate systems obtained using different image analysis techniques. The report describes and discusses a number of shape factors that are widely used in pharmaceutical research. Using photographs of 16 pellets of different shapes, obtained by extrusion-spheronization, we investigated how shape factor estimates vary depending on method of calculation, and among different software packages. The results obtained indicate that the algorithms used (both for estimation of basic dimensions such as perimeter and maximum diameter, and for estimation of shape factors on the basis of these basic dimensions) have marked influences on the shape factor values obtained. These findings suggest that care is required when comparing results obtained using different image analysis programs.

Extruded and Spheronized Beads Containing No Microcrystalline Cellulose: Influence of Formulation and Process Variables

The purposes of this study were to investigate the use of chitosan in the manufacture of beads by extrusion-spheronization without inclusion of microcrystalline cellulose, and to study the effect of formulation and process variables on the characteristics of the beads. Beads containing chitosan, fine particle ethylcellulose, hydroxypropyl methylcellulose (HPMC), and caffeine as the model drug were manufactured. Bead size, yield, shape, friability, density, porosity, and release studies were determined. Spherical beads with good mechanical properties could be manufactured without microcrystalline cellulose. Release studies showed that there was immediate release of drug from the beads. A five factor, half fraction screening design was employed to study the effect of formulation variables and process variables on the properties of the beads. Statistical analysis indicated that formulation variables such as the chitosan content, HPMC content, and water content, and process variables such as the spheronizer speed and extruder speed significantly affected the physical properties of the beads. The bead size decreased with an increase in chitosan content. Significant two-factor interactions exist between the variables for several of the measured responses. Beads with high percentage yield and high sphericity can be obtained at high chitosan content, and low HPMC content, water content, spheronizer speed, and extruder speed. Less friable beads can be obtained at high levels of studied formulation variables and low levels of studied process variables. Beads of high density and low porosity can be manufactured at high levels of the studied formulation and process variables. Regression equations were generated using Statgraphics Plus software that can be used to develop formulations with desired bead properties. Chitosan was useful to provide beads of acceptable physical properties using water as a granulating fluid in the extrusion-spheronization process.

Preparation of pellets of different shape and their characterization

Pellets of different shapes were produced by modifying the processing parameters of a standardized pellet formulation. The target size of these pellets was 1-1.4 mm. Initially the shape of the pellets was assessed by visual observation. In total, eight batches of pellets were produced of which four were considered to be round, whereas the other four deviated from the spherical shape by various degrees. The different pellet fractions were then characterized for their size, shape, surface, and density properties employing a series of established techniques in order to identify the most appropriate method of characterization and the interrelationships between these properties. The results showed that attempting a task of preparing pellets of graded differences in shape from the same powder blend can result in changes of other important pellet properties such as surface roughness, surface area, and pellet dimensions. Some of these changes could be anticipated by considering the process variables involved, whereas others changed in a manner for which there is no immediate explanation.

Emulsion/solvent evaporation as an alternative technique in pellet preparation

Paracetamol/Eudragit RS, paracetamol/ethylcellulose, and paracetamol/cellulose acetate pellets of different drug/polymer ratios (w/w) were prepared by the dissolution/solvent evaporation technique. These pellets were then characterized by particle size distribution analysis, ultraviolet (UV) spectroscopy, differential thermal analysis, and scanning electron microscopy (SEM). Hard gelatin capsules were filled with each particle size fraction of these pellets, and in vitro dissolution studies were performed to verify the capability of each series of pellets to control drug release. Pellets were spherical, presented a polynucleated microcapsule structure, and under certain experimental conditions, the yield of the preparation process reached very high values. The dissolution studies pointed out the slow paracetamol release from these pellets.

Characterization of wet masses of pharmaceutical powders by triaxial compression test

The mechanical and rheologic properties of wet masses of pharmaceutical powders determine their processibility and the quality of the product prepared by extrusion/spheronization. In this work, a triaxial compression test was attempted for the first time to characterize material properties of pharmaceutical wet masses of different hydrophilicity and particle sizes. The stress-strain curves and the pore pressure were determined at various cell pressures. The failure criteria of the wet masses were obtained from the stress path on the deviator stress plane. The cohesion (c) and the angle of internal friction (phi) were evaluated from the intercept and the slope of the failure loci. The stress-strain behavior strongly depended on the type of powders and cell pressure. The values of c and phi were similar for wet masses of EC FP, MCC PH101, and SMCC 50, but a very small phi and a very high c value for HPMC. The shear strength and rigidity of the wet masses were in the order of EC FP > SMCC 50 > MCC PH101 > HPMC, whereas the elastic recovery was in the opposite order. These material parameters could be used as references for selection of excipients and formulation for extrusion/spheronization.

Evaluation of a standardised procedure to assess the shape of pellets using image analysis

The influence of threshold definition, number of pellets counted, image magnification and lightning technique on the assessment of pellet shape has been investigated using three batches of pellets and an image analysis system. The pellet parameters measured were 'aspect ratio', 'circularity', 'projection sphericity', 'e(R)' and 'Feret diameter.' The methodical error, reproducibility and repeatability of the results were chosen as statistical test parameters. The position of the light source is crucial in providing an accurate particle size value. Top light was identified as the illumination technique that gave a mean pellet size similar to the true pellet size. The use of a light table produced significantly larger pellet size values. A minimum pixel resolution appears necessary for an accurate shape parameter definition. One pixel should not cover more than 30 microm for pellets of an average particle size of 1.2 mm. Shape descriptors, which are based on a multiple combination of area and perimeter data such as the circularity, are greatly dependent on the number of pellets counted. Shape factors, which do not (aspect ratio) or only as a single value do involve an area or perimeter measurement (e(R), projection sphericity) are, however, nearly independent of the number of pellets counted, as long as the magnification is sufficiently large and the pellets are randomly drawn from the batch. For nearly spherical particles, the methodical error is below 1%, but for elongated particles this error can reach 5%. The repeatability is also very good for nearly spherical particles (<2%), but increases to very large values if the particles are clearly elongated. The limiting values for the various shape factors should be reconsidered. An upper value for the aspect ratio of 1.1 and a lower value of 0.6 for e(R) are recommended. The circularity should not be used as the shape factor to characterise spheres, because errors in image recognition can affect strongly the applicability of this shape factor. The projection sphericity has only a limited sensitivity to variations in particle shape.

The use of beta-cyclodextrin as a pelletization agent in the extrusion/spheronization process

The use of beta-cyclodextrin for the preparation of pellets by the extrusion/spheronization process is described for different formulations and processing conditions. Sieve analysis and friability tests were performed to assess the physical and technological characteristics of pellets. Satisfactory products were obtained with beta-cyclodextrin contents up to 90% by weight.

Effect of common classes of excipients on extrusion-spheronization

Different classes of excipients with potential for use in the design of novel pelletized formulations manufactured by extrusion-spheronization were examined using factorial experiments. Among the various silicates examined in a model mix with microcrystalline cellulose and lactose wetted with water, kaolin, talc and Veegum F provided improved plasticity for the formation of spherical pellets. Weak bases such sodium bicarbonate and weak acids such as fumaric acid also aided spheronization. Whereas waxy materials such as hydrogenated castor oil and Precirol ATO5, and wetting agent such as sodium lauryl sulphate improved sphericity, these excipients reduced pellet yield by favouring agglomeration. Other materials promoting unwanted formation of over-size pellets were bentonite, citric acid and tartaric acid. The inclusion of Bentone 27, various hydroxide and carbonate bases, and fumaric acid favoured fines production. Collectively the results showed that within classes of excipients, it was not possible to predict the effect of different materials on pellet yield and sphericity. However, Carr's index and Hausner ratio calculated from density determinations correlated well with sphericity measured by image analysis.

Drug solubility effects on predicting optimum conditions for extrusion and spheronization of pellets

This paper explores the utility of aqueous solubility of structurally similar drugs in predicting optimum conditions for extrusion and spheronization of pellets using response surface methodology. Pharmacologically active xanthine derivatives exhibiting widely varying aqueous solubility were used to determine optimum conditions for pelletization. The amount of water added to the formulation, wet mixing time, and spheronizing time were explored in a series of central composite experimental designs to exhaustively explore and mathematically model the response surfaces for each drug. Using a marketed microcrystalline cellulose excipient, optimum extrusion and spheronization conditions for less soluble drugs required more water, a longer wet mixing time, and prolonged spheronizing times. Results were similar when a new microcrystalline cellulose was substituted, except that more water was required. When comparing results for different drugs, a strong linear relationship was observed between the aqueous solubility of the drug and the water content required for optimum pellet production. The water content range over which quality pellets could be produced was much broader for poorly soluble drugs. Aqueous solubility of the active component appears to be a good predictor for the water requirements for optimum extrusion and spheronization of pellets for pharmaceutical applications.

The power-consumption-controlled extruder: a tool for pellet production

Based on the assumption that there is a link between power consumption of an extruder and pellet properties, a control circuit for power consumption was developed. Powder and granulation liquid are fed separately into a twin-screw extruder. The power consumption is controlled by varying the pump rate at a given powder-feed rate; consequently each level of power consumption results in a specific water content of the extrudate for a particular formulation. The shape of pellets depends almost entirely on the level of power consumption irrespective of formulation. The size of dry pellets is additionally affected by a shrinking factor which depends on the water content. The power-consumption-controlled extruder is an appropriate tool for the production of pellets. The system is able to adapt the water content for a formulation automatically.