Impact of solid-state properties on lubrication efficacy of magnesium stearate

Tablet ejection: A systematic comparison between force, static friction, and kinetic friction

The magnitude of the frictional forces during the ejection of porous pharmaceutical tablets plays an important role in determining the occurrence of tabletting defects. Here, we perform a systematic comparison between the maximum ejection force, static friction coefficient, and kinetic friction coefficient. All of these metrics have different physical meanings, corresponding to different stages of ejection. However, experimental limitations have previously complicated comparisons, as static and kinetic friction could not be measured simultaneously. This study presents a method for simultaneously measuring the maximum ejection force, static friction coefficient, and kinetic friction coefficient in situ during tablet ejection in routine compaction simulator experiments. Using this method, we performed a systematic comparison, including variations of (1) ejection speed, (2) compaction pressure, (3) material, and (4) lubrication method. The relative importance of each variable is discussed in detail, including how ejection speed alone can be a decisive factor in tablet chipping. The reliability of the newly developed method is supported by excellent agreement with previous studies and finite element method (FEM) simulations. Finally, we discuss the suitability of friction coefficients derived from Janssen-Walker theory and explanations for the phenomenon of die-wall static friction coefficients with apparent values far above unity.

Effect of magnesium stearate solid lipid nanoparticles as a lubricant on the properties of tablets by direct compression

This study discusses the lubricant properties of magnesium stearate solid lipid nanoparticles (MgSt-SLN) and their effect on the tabletability, mechanical properties, disintegration, and acetaminophen-model dissolution time of microcrystalline cellulose (MCC) tablets prepared by direct compression. The behavior of MgSt-SLN was compared to reference material (RM) to identify advantages and drawbacks. The nanoprecipitation/ion exchange method was employed to prepare the MgSt-SLN. Particle size, zeta potential, specific surface area, morphology, and true density were measured to characterize the nanosystem. The MgSt-SLN particle sizes obtained were 240 ± 5 nm with a specific surface area of 12.2 m2/g. The MCC tablets with MgSt-SLN presented a reduction greater than 20 % in their ejection force, good tabletability, higher tensile strength, lower disintegration delay, and marked differences in acetaminophen dissolution when compared to the RM. The reduced particle size of the magnesium stearate seems to offer a promising technological advantage as an efficient lubricant process that does not affect the properties of tablets.

Investigation of Dispersion Kinetics of Particulate Lubricants and their Effect on the Mechanical Strength of MCC Tablets

INTRODUCTION

Tablets are commonly produced by internally adding particulate lubricants, which are known to possibly lower the mechanical strength of tablets. This reduction is caused by the coverage of matrix forming components by lubricant particles, resulting in decreased interparticulate interactions. The known incompatibilities with some active compounds of the predominantly used lubricant, magnesium stearate, call for the in-depth characterization of alternative lubricants.

PURPOSE

Investigation of the dispersion behavior of five commonly applied pharmaceutical lubricants by mathematically modeling the dispersion kinetics for short and extended mixing times.

METHODS

The dispersion behavior of five different pharmaceutical lubricants were examined by systematically varying lubricant concentration and mixing time of binary formulations and evaluating the kinetic of tensile strength reduction by theoretically estimating the surface coverage based on particle sizes.

RESULTS

For short mixing times, a unifying relationship between compactibility reduction and theoretical surface coverage was identified. Subsequently, for extended mixing times, distinct differences in the shear strength and dispersion kinetics of the investigated lubricants were found.

CONCLUSIONS

The lubricant particle size controls the tensile strength reduction if short mixing times are applied. For extended mixing times, the investigated lubricants can be divided into two groups in terms of dispersion kinetics. Possible underlying reasons are discussed in detail in order to enhance the general understanding of lubricant dispersions in tablet formulations.

The effect of relative humidity and formulation variables on chewable xylitol-sorbitol tablets

Changing relative humidity levels challenge the manufacturing of chewable xylitol-sorbitol based tablets. The aim of the study is to investigate how the formulation of chewable xylitol-sorbitol tablets affects the properties of the powder blends and the tablets in an environment of different relative humidity levels. In all, 30 batches containing different ratios of sorbitol, xylitol and magnesium stearate were prepared at three different relative humidity levels. Powder blends were made into tablets using an instrumented eccentric tableting machine. To demonstrate the effect of variables on powder blend and tablet properties, multiple linear regression analysis was performed. It was found that xylitol-sorbitol powder blends and tablets benefitted from the large amount of magnesium stearate, and the high lubricant level negatively affected the quality of the tablets only at high relative humidity. In the presence of high environmental humidity, the amount of sorbitol in the powder mixture must be limited in order to prevent sticking whereas at low relative humidity, higher content of sorbitol is needed to decrease the friability of tablets. Results indicate that alternating relative humidity levels truly challenge the production of xylitol-sorbitol based tablets and if the humidity is not controllable, there is a need for additional filler-binders.

The impact of solid-state form, water content and surface area of magnesium stearate on lubrication efficiency, tabletability, and dissolution

Magnesium stearate (MgSt) is a widely used pharmaceutical lubricant in tablet manufacturing. However, batch-to-batch variability in hydrate form and surface area can lead to inconsistency in tablet performance. In this work, several unique MgSt samples were studied: traditional monohydrate samples with high surface area, dihydrate forms with high and low surface area, and disordered forms with low and medium water content. The effects of solid-state form and particle properties on lubrication efficiency, tabletability and dissolution were studied for tablets in a model direct compression formulation. It was found that the monohydrate and dihydrate forms had good lubrication efficiency compared to the disordered form, while the disordered form had the best tabletability. The dissolution rate correlated with surface area, where slower dissolution rates corresponded with higher MgSt surface areas. The dihydrate sample with lower surface area had the best performance for this model formulation, in terms of lubrication efficiency, tabletability and dissolution. Overall, it is concluded that the choice of the most appropriate grade of MgSt for a particular formulation depends on a comprehensive evaluation of the impact of MgSt properties on lubrication efficiency, tabletability and dissolution.

Development and characterization of metformin hydrochloride- and glyburide-containing orally disintegrating tablets

Diabetes is characterized by chronic hyperglycemia. Although metformin hydrochloride (MHCl)- and glyburide (GLB)-containing conventional tablets are available in the market and used to treat diabetes, orally disintegrating tablets (ODTs) containing the combination of these drugs are not commercially available. Therefore, the aim of this study was to prepare ODTs containing MHCl and GLB by direct-compression (DC-ODTs) and freeze-drying (FD-ODTs) methods. Physical properties of the powder mixture of DC-ODT formulation were determined (Angle of repose: 37.18 ± 1.27°; compressibility index: 20.31 ± 1.06%; Hausner ratio: 1.25 ± 0.03). Its moisture content was 0.3 ± 0.09%. The hardness values and the disintegration times for DC-ODTs and FD-ODTs were 221.60 ± 40.82 and 66.54 ± 2.68 N, and 80 and 30 s, respectively. Friability values were 0.24% for DC-ODTs and 0.38% for FD-ODTs. In uniformity-of-mass for single-dose-preparations test, the average weight was 684.38 ± 1.97 mg for DC-ODTs and 342.93 ± 2.4 mg for FD-ODTs, with less than 5% deviation for all 20 tablets. Water-absorption ratio for DC-ODTs was 1.30 ± 0.05. More than 90% of MHCl and GLB were dissolved within 5 min in both DC-ODTs and FD-ODTs. Although Caco-2 permeability of MHCl was influenced by the ODTs, GLB permeability was not. These results indicated that MHCl- and GLB-containing ODTs may be used as promising formulations for the treatment of diabetes.

Compatibility study of rosmarinic acid with excipients used in pharmaceutical solid dosage forms using thermal and non-thermal techniques

Rosmarinic acid (RA) is a phenolic compound that presents well-documented anti-inflammatory, antioxidant and antitumor activities, and based on its pharmacological potential and poor bioavailability, several solid dosage forms have been developed to RA delivery. Therefore, in literature, there are no reports about RA compatibility with excipients. In this regard, the aim of the present study was to evaluate, for the first time, the compatibility of RA with excipients commonly used in solid dosage forms at a 1:1 (RA:excipient) ratio using differential scanning calorimetry (DSC), thermogravimetry (TG), Fourier-transform infrared (FTIR), solid-state nuclear magnetic resonance (ssNMR), and isothermal stress testing (IST) coupled with liquid chromatography (LC). The excipients selected were hydroxypropyl methylcellulose (HPMC), microcrystalline cellulose (MCC), lactose monohydrate (LAC), polyvinylpyrrolidone (PVP), talc (TALC), croscarmellose sodium (CCS), and magnesium stearate (MgSTE). According to DSC results, physical interactions were found between RA and HPMC, LAC, CCS, and MgSTE. The TG analyses confirmed the physical interactions and suggested chemical incompatibility. FTIR revealed physical interaction of RA with TALC and MgSTE and the ssNMR confirmed the physical interaction showed by FTIR and excluded the presence of chemical incompatibility. By IST, the greatest loss of RA content was found to CCS and MgSTE (>15%), demonstrating chemical incompatibilities with RA. High temperatures used in DSC and TG analyses could be responsible for incompatibilities in binary mixtures (BMs) with HPMC and LAC, while temperature above 25 °C and presence of water were factors that promote incompatibilities in BMs with CCS and MgSTE. Overall results demonstrate that RA was compatible with MCC and PVP.

Elucidating the Variability of Magnesium Stearate and the Correlations With Its Spectroscopic Features

The objective of this study is to investigate the variability in physiochemical and spectral properties of commercially available vegetable-grade magnesium stearate (MgSt) samples and to assess the correlation between physiochemical properties and near-infrared and Raman spectroscopic features to determine if fast spectral measurements could be used for physical and chemical evaluation. Thirteen MgSt samples of 9 manufacturer grades were obtained from 3 suppliers. The chemical composition was examined using gas chromatography and loss on drying. The physical characteristics were examined on 3 levels: solid state, particle, and bulk level. Comparing the largest to the smallest test values of 13 samples, the variation of the properties ranged from 7% to 335%, with majority of them varying by more than 100% of the smallest value. The samples could be categorized into 4 groups based on solid state properties (1) monohydrate, (2) dihydrate, (3) mixture of monohydrate and dihydrate, and (4) anhydrous form. Scanning electron microscopy images revealed 2 morphological types: thin, flat, and plate-like crystal habit versus irregular crystal habit. The overall variability was mapped using Principal Component Analysis. The greatest variation was due to different manufacturers and perhaps manufacturing methods and starting materials. Based on correlations to physiochemical properties of MgSt, near-infrared and Raman spectra showed potential as a rapid technique for evaluating the differences in excipient properties.

Evaluation of the lubricating effect of magnesium stearate and glyceryl behenate solid lipid nanoparticles in a direct compression process

The aim of this study was to develop solid lipid nanoparticles (SLN) and introduce them into a direct compression process to evaluate their lubricant properties. The study consisted of preparing glyceryl behenate SLN (Compritol® 888 ATO) by hot dispersion, and magnesium stearate SLN by a novel nanoprecipitation/ion exchange method. The ejection force was measured for nanosystems and raw materials in a formulation typically used for direct compression. The smallest particle sizes obtained were 456 nm for Compritol® 888 ATO and 330 nm for magnesium stearate. Results show that the NPs used as lubricants in a direct compression model formulation provided efficient lubrication by maintaining the lubricating properties of the system, thereby decreasing the amount of lubricant used compared to the raw material. The lubricating effect showed an increase of 15-30% for magnesium stearate and Compritol® 888 ATO, compared to the raw material at concentrations above 2%.

Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS): A Novel Approach To Investigate the Wettability of Pharmaceutical Powder Blends

The ability of broadband acoustic resonance dissolution spectroscopy (BARDS) to assess the wettability of powder blends is investigated. BARDS is a novel analytical technology developed on the basis of the change in acoustic phenomena observed when material is added into a solvent under resonance. Addition of solid material to the solvent results in the introduction of gas (air) into the solvent, changing the compressibility of the solvent system, and reducing the velocity of sound in the solvent. As a material is wetted and dissolved, the gas is released from the solvent and resonance frequency is altered. The main purpose of this work is to demonstrate the ability of BARDS to assess differences in the wetting behavior of tablet excipients (microcrystalline cellulose (MCC) and magnesium stearate (MgSt)) and a model drug (metoclopramide hydrochloride) as single component powders and multicomponent powder blends. BARDS acoustic responses showed a prolonged release of gas for the powdered blends with lubricant compared to unlubricated blends. As the elimination of gas from the solvent was assumed to follow first order elimination kinetics, a compressible gas elimination rate constant was calculated from the log plots of the gas volume profiles. The gas elimination rate constant was used as a parameter to compare the release of gas from the powder introduced to the solvent and hence the powder wetting behavior. A lower gas elimination rate constant was measured for lubricated blends compared to nonlubricated blends, suggesting the prolonged hydration of lubricated blends. Standard wetting techniques such as contact angle measurements and wetting time analysis were also used to analyze the blends and confirmed differences in wetting behavior determined by BARDS. The study results demonstrate the capability of BARDS as a rapid, analytical tool to determine the wetting behavior of the pharmaceutical powder blends and the potential of BARDS as a process analytical technology (PAT) tool.

Characterization of Synthesized and Commercial Forms of Magnesium Stearate Using Differential Scanning Calorimetry, Thermogravimetric Analysis, Powder X-Ray Diffraction, and Solid-State NMR Spectroscopy

Magnesium stearate is the salt of a complex mixture of fatty acids, with the majority being stearate and palmitate. It has multiple crystalline forms and, potentially, an amorphous form. Magnesium stearate is used in the pharmaceutical manufacturing industry as a powder lubricant, and typically is added at low levels (∼1%) during the manufacturing process and blended for a relatively short time (∼5 min). Proper levels and mixing times are needed, as too short a mixing time or too small a quantity will result in improper lubrication, and too much can negatively impact dissolution rates. The complex mixture of multiple fatty acids and crystalline forms in magnesium stearate leads to variability between commercial sources, and switching between sources can impact both the amount of lubricant and mixing time needed for proper lubrication. In order to better understand the complex nature of magnesium stearate, a variety of analytical techniques were used to characterize both synthesized and commercial magnesium stearate samples. The results show that correlation among differential scanning calorimetry, thermogravimetric analysis, solid-state NMR spectroscopy, and other techniques provides a unique insight into the forms of magnesium stearate. Finally, the ability to monitor form changes of magnesium stearate in an intact tablet using solid-state NMR spectroscopy is shown.

Impact of moisture and magnesium stearate functionality on manufacturability of wet granulated metformin tablets

During the development of a wet granulated 850 mg metformin hydrochloride tablet formulation, the tablets exhibited high friability (>3% w/w) irrespective of the source of extra-granular magnesium stearate (MgSt). High friability values indicated that an anti-bonding effect of MgSt was too high to be overcome by 3.3% w/w povidone as a binder in the formulation with 1.5% w/w residual granule moisture. Increasing the povidone concentration up to 7% w/w showed limited improvement in friability, with tablets showing variable friability depending on MgSt source. Characterization of MgSt indicated differences in crystallinity, surface area and particle morphology between different vendors. In addition, a new bulk yield strength test, which determines the MgSt fragmentation tendency, was found to be indicative of the MgSt performance in the tablet formulation. To improve bonding properties of granules, residual granule moisture was increased to 2% w/w at different povidone concentrations. At 2% w/w residual granule moisture content, regardless of MgSt source, the tablets showed significant improvement in friability (∼0.6% w/w) even at the lowest povidone concentration (3.3% w/w). The bonding power of higher residual granule moisture had a greater impact than higher povidone concentration in overcoming the anti-bonding effects of magnesium stearate.

New approach to evaluate the lubrication process in various granule filling levels and rotating mixer sizes using a thermal effusivity sensor

The principles of thermal effusivity are applied to an understanding of the detailed mechanisms of the lubrication process in a rotating mixer. The relationships and impact of the lubrication process by the pattern of powder flow, the filling level, and the rotating mixer size were investigated. Thermal effusivity profiles of the lubrication process, as obtained, indicate that lubrication is a two-phase process. The intersection point of the first and second phases (IPFS) is influenced by changing the filling level, thus changing the resulting number of avalanche flows created. The slope of the second phase (SSP) is influenced by the relationship between the number and the length of avalanche flows. Understanding this difference between the first and second phases is important to successfully evaluate the impact of proposed changes in the lubrication process. From this knowledge, a predictive model of the lubrication profile can be generated to allow an evaluation of proposed changes to the lubrication process. This model allows estimation of the lubrication profile at different filling levels and in different rotating mixer sizes. In this study, the actual lubrication profile almost coincides with the model predicted lubrication profile. Based on these findings, it is assumed that lubrication profiles at a commercial scale can be predicted from data generated at the laboratory scale. Further, it is assumed that changes in the filling level can also be estimated from the laboratory or current data.

Effect of force feeder on tablet strength during compression

Mechanical strength of tablets is an important quality attribute, which depends on both formulation and process. In this study, the effect of process variables during compression on tablet tensile strength and tabletability (the ratio of tensile strength to compression pressure) was investigated using a model formulation. Increase in turret and force feeder speeds reduced tablet tensile strength and tabletability. Turret speed affected tabletability through changes in dwell time under the compression cam and the kinetics of consolidation of granules in the die cavity. The effect of force feeder was attributed to the shearing of the granulation, leading to its over-lubrication. A dimensionless equation was derived to estimate total shear imparted by the force feeder on the granulation in terms of a shear number. Scale-independence of the relationship of tabletability with the shear number was explored on a 6-station Korsch press, a 16-station Betapress, and a 35-station Korsch XL-400 press. The use of this relationship, the exact nature of which may be formulation dependent, during tablet development is expected to provide guidance to the scale-up and interchangeability of tablet presses.

Coprocessing of nevirapine and stavudine by spray drying

The objective of the present study was to coprocess 2 active pharmaceutical ingredients (APIs), nevirapine (NVP) and stavudine (STV), by spray drying technique to overcome the respective problems of poor solubility and poor content uniformity. The coprocessed product (NVP-STV CP) and untreated APIs were characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle size, surface area analysis, compressibility, and solubility. Coprocessing enhanced NVP solubility by approximately 1.5 fold and provided uniform distribution of low-dose STV in the formulation composite. Phase solubility studies elucidated the mechanism of enhanced NVP solubility. The coprocessed product was stable under accelerated stability conditions of 40 degrees C/75% relative humidity (RH) for 3 months. The coprocessed product was formulated into 3 drug fixed dose combination (FDC) tablets with lamivudine (LMV), which gave an enhanced in vitro NVP drug release compared with the control formulation. Spray drying as a coprocessing technique optimally utilized the individual components of the antiretroviral FDC tablets and synergistically enhanced the performance attributes.

Near Infrared Spectroscopy of Magnesium Stearate Hydrates and Multivariate Calibration of Pseudopolymorph Composition

Samples of magnesium stearate monohydrate and dihydrate were used to prepare standard mixtures of known pseudopolymorphic composition. Near infrared spectra (NIR) of the standard mixtures were measured to develop multivariate calibration models for the pseudopolymorphic composition of magnesium stearate by partial least squares (PLS) regression. Magnesium stearate hydrate compositions of the standard mixtures were compared against the hydrate composition based on thermogravimetric analysis (TGA). The mixture compositions determined from TGA mass loss on drying (LOD) measurements were found to be inaccurate. PLS regression was applied to the TGA thermograms of the standard mixtures to generate more accurate reference values, and this model was then applied to a set of validation samples. Application of the NIR PLS model to the validation sample set resulted in precise estimates of sample pseudopolymorphic composition when compared to the TGA PLS reference values. The NIR PLS model was found to be more sensitive than TGA LOD to small quantities of hydrates, and the TGA PLS model was also found to be more sensitive that TGA LOD. The results demonstrate the challenges and opportunities that arise when rapid, nondestructive spectroscopic methods depend on insensitive or inaccurate reference methods for development of multivariate calibration models.

Lubrication potential of magnesium stearate studied on instrumented rotary tablet press

The aim of this study was to investigate the lubrication potential of 2 grades of magnesium stearate (MS) blended with a mix of dicalcium phosphate dihydrate and microcrystalline cellulose. Force-displacement, force-time, and ejection profiles were generated using an instrumented rotary tablet press, and the effect of MS mixing time (10, 20, and 30 minutes) and tableting speed (10.7, 13.8, and 17.5 rpm) was investigated. The packing index (PI), frictional index (FI), and packing energy (PE) derived from the force-displacement profiles showed that MS sample I performed better than sample II. At higher lubricant mixing times, the values of PI were observed to increase, and values of FI and PE were observed to decrease for both MS samples. Lower values of area under the curve (AUC) calculated from force-time compression profiles also showed sample I to be superior to sample II in lubrication potential. For both the samples, the values of AUC were observed to decrease with higher lubricant mixing times. Tapping volumetry that simulates the initial particle rearrangement gave values of parameter a and C(max) that were higher for sample I than sample II and also increased with lubricant mixing time. The superior lubrication potential of sample I was also established by the lower values of peak ejection force encountered in the ejection profile. Lower ejection forces were also found to result from higher tableting speeds and longer lubricant mixing times. The difference in lubrication efficacy of the 2 samples could be attributed to differences in their solid-state properties, such as particle size, specific surface area, and d-spacing.