Deformation kinetics of acetaminophen crystals

Sodium lauryl sulfate as lubricant in tablets formulations: Is it worth?

Lubricants are excipients used in tablet formulations to reduce friction and adhesion forces within the die or on the punches surface during the manufacturing process. Despite these excipients are always required for the tablets production, their amount must be carefully evaluated since lubricants can negatively impact on mechanical strength, disintegration and dissolution behavior of solid dosage forms. Alternative compounds have been suggested to overcome the issues of conventional lubricants and sodium lauryl sulfate (SDS) is one of the most promising one. Despite SDS has been object of several investigations, a definitive conclusion on its effectiveness cannot still be drawn. Particularly, its efficacy on tablets disaggregation and API dissolution is still unclear. Here, the effect of SDS on all the relevant features of tablets and tableting process has been evaluated on immediate release hydrophobic tablets formulations in comparison with conventional lubricants. The results of this investigation are quite outspoken: SDS has a low lubricant power while it determines only a limited improvement on tablets hardness. It greatly improves the tablets wettability but only on model formulations, the presence of superdisintegrants resets its effectiveness and any possible effect on tablets disaggregation. None of the tested formulations showed improvement on the API dissolution rate.

Study of Diminutive Granules as Feed Powders for Manufacturability of High Drug Load Minitablets

The maximal amount of drug contained in a minitablet is limited. To reduce the total number of minitablets in a single dose, high drug load minitablets can be prepared from high drug load feed powders by various pharmaceutical processing techniques. Few researchers have however examined the influence of pharmaceutical processing techniques on the properties of high drug load feed powders, and consequently the manufacturability of high drug load minitablets. In this study, silicification of the high drug load physical mix feed powders alone did not yield satisfactory quality attributes and compaction parameters to produce good quality minitablets. The abrasive nature of fumed silica increased ejection force and damage to the compaction tools. Granulation of fine paracetamol powder was crucial for the preparation of good quality high drug load minitablets. The diminutive granules had superior powder packing and flow properties for homogenous and consistent filling of the small die cavities when preparing minitablets. Compared to the physical mix feed powders for direct compression, the granules which possessed higher plasticity, lower rearrangement and elastic energies, yielded better quality minitablets with high tensile strength and rapid disintegration time. High shear granulation demonstrated greater process robustness than fluid bed granulation, with less discernment on the quality attributes of feed powder. It could proceed without fumed silica, with the high shear forces reducing interparticulate cohesivity. An in-depth understanding on the properties of high drug load feed powders with inherently poor compactability and poor flowability is important for the manufacturability of high drug load minitablets.

Systematic approach to elucidate compaction behavior of acyclovir using a compaction simulator

In this research, various approaches were attempted with a compaction simulator to investigate the unidentified compaction behavior of acyclovir, a model compound. Various indicators for the compaction behavior of acyclovir were obtained and compared with those of three commonly used excipients with relatively well-known compaction behavior. From two frequently used powder compaction models, the Heckel and Walker models, curvature of plot, yield stress, D₀, SRS value, and W value were acquired. In addition, compression and elastic energies were obtained during the loading and unloading phases, respectively. The ratio of the two energies was also utilized. To characterize the mechanical properties of materials during bond formation, the radial tensile strength of powder compacts was measured. For all evaluations, the effects of compaction rate and lubrication were studied simultaneously. We found that primary particles of acyclovir were compacted mainly by plastic flow, with high viscoelasticity and low particle interactions. Their bond formation was highly sensitive to strain rate and lubrication. This study showed the potential application of a compaction simulator to elucidate the compaction behavior of a material of interest.

Structural heterogeneity of pharmaceutical compacts probed by micro-indentation

Indentation has been used for several decades to conveniently assess the hardness and modulus of various compacts. However, this measurement is dependent on the size of the indentation area from a few nanometers to several millimeters, which is determined by the maximum indentation force (MIF). Micro-indentation often loses its ability to give an accurate representation of the hardness due to its relatively small micron-size indentation area compared with the dimensions of the structural inhomogeneity of compacts. This study used a different approach to micro-indentation by examining whether this method can probe the inhomogeneity of compacts with varying MIF. Two typical pharmaceutical excipients, one brittle and one ductile, were used as model compacts. The representative hardness and modulus values were available when the MIF was >1000 mN. Changes in the standard deviation of the indentation hardness reflected the structural inhomogeneity of the compacts, which was found to increase with decreasing MIF to below 800 mN in the case of the microcrystalline cellulose compacts. The information on the structural inhomogeneity obtained by micro-indentation appears to be consistent with the observations from microscopy investigations. Anisotropy and other related structural information could be readily obtained by probing the two different surfaces of compacts with changing MIF, one parallel and the other perpendicular to the compaction pressure direction.

Measurement of Process-Dependent Material Properties of Pharmaceutical Solids by Nanoindentation

The purpose of this work was to evaluate nanoindentation as a means to characterize the material properties of pharmaceutical solids. X-ray diffraction of potassium chloride and acetaminophen showed that samples prepared by cooling a melt to a crystalline sample as opposed to slow recrystallization had the same crystal structure. With analysis of the force-displacement curves, the KCl quenched samples had a hardness that was 10 times higher than the recrystallized KCl, while acetaminophen quenched samples were 25% harder than the recrystallized samples. The elastic moduli of the quenched samples were also much greater than that observed for the recrystallized samples. Although the elasticity was independent of load, the hardness increased with load for acetaminophen. With each sample, the flow at constant load increased with applied load. Etching patterns obtained by atomic force microscopy showed that the KCl quenched sample had a higher dislocation density than the recrystallized sample, although there was no evident difference in the acetaminophen samples. Overall, the differences in the observed sample properties may be related to the dislocation density. Thus, nanoindentation has been shown to be a sensitive method for determining a processed-induced change in the hardness, creep, and elasticity of KCl and acetaminophen.

Characterization of pharmaceutical solids by scanning probe microscopy

The force-displacement profiles of four well-characterized materials that represent both soft/hard and plastic/brittle materials have been obtained using a novel nanoindentation technique. Flat surfaces of acetaminophen, potassium chloride, sucrose, and sodium stearate were prepared by melting or recrystallization, and the melting points were measured. Topographic and the corresponding first derivative images were obtained both before and after indentation. The materials were indented using a 10 s loading time, followed by a 2 s hold, and ending with a 10 s unloading time thereby providing a unique force-displacement profile for each material. The loading profile of acetaminophen was discontinuous, whereas the profiles for the other three materials were smooth. The profiles were analyzed and the rank order of hardness was sucrose > acetaminophen > KCl > sodium stearate, which is consistent with the literature. The rank order of the stiffness, which is related to the modulus of elasticity, was sucrose > KCl > acetaminophen > sodium stearate. Given the flexibility and power of this approach, nanoindentation coupled with atomic force microscopy may be a useful means to characterize materials for evaluating tablet-processing conditions, perhaps at a preformulation stage.