Comparative evaluation of tablet lubricants: effect of application method on tablet hardness and ejectability after compression

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.

Prediction of the impact of lubrication on tablet compactibility

The tableting of most pharmaceutical formulations requires the addition of lubricants to reduce ejection forces, prevent tooling damage and tablet defects. The internal addition of lubricants is known to reduce tablet tensile strength, especially of mainly plastically deforming materials. To date, available models show only limited quantitative predictive accuracy for the influence of lubricant concentration on the mechanical strength of tablets. This study aims to fill this gap and present a model based on the Ryshkewitch-Duckworth equation that can estimate the compactibility profiles of lubricated formulations. Binary mixtures of different diluents (microcrystalline cellulose and lactose) were prepared with common lubricants (magnesium stearate and sodium stearyl fumarate) and subsequently tableted. The resulting compactibility profiles were fitted using the Ryshkewitch-Duckworth equation and the derived fit parameters (k_b and σ₀) were correlated with the lubricant concentration. Subsequently, an empirical model was established which requires a minimum of experimental data and is able to predict the tensile strength of lubricated diluent tablets. Consequently, the developed empirical model is an interesting and valuable addition to the existing multi-component compacting models available and offers the opportunity to accelerate experimentation in the development of new tablet formulations.

Multi-dimensional visualization for the morphology of lubricant stearic acid particles and their distribution in tablets

The shapes of particles and their distribution in tablets, controlled by pretreatment and tableting process, determine the pharmaceutical performance of excipient like lubricant. This study aims to provide deeper insights to the relationship of the morphology and spatial distribution of stearic acid (SA) with the lubrication efficiency, as well as the resulting tablet property. Unmodified SA particles as flat sheet-like particles were firstly reprocessed by emulsification in hot water to obtain the reprocessed SA particles with spherical morphology. The three-dimensional (3D) information of SA particles in tablets was detected by a quantitative and non-invasive 3D structure elucidation technique, namely, synchrotron radiation X-ray micro-computed tomography (SR-µCT). SA particles in glipizide tablets prepared by using unmodified SA (GUT), reprocessed SA (GRT), as well as reference listed drug (RLD) of glipizide tablets were analyzed by SR-µCT. The results showed that the reprocessed SA with better flowability contributed to similarity of breaking forces between that of GRT and RLD. SA particles in GRT were very similar to those in RLD with uniform morphology and particle size, while SA particles in GUT were not evenly distributed. These findings not only demonstrated the feasibility of SR-µCT as a new method in revealing the morphology and spatial distribution of excipient in drug delivery system, but also deepened insights of solid dosage form design into a new scale by powder engineering.

Evaluation of Dissolution Profile between Original and Generic Products of Zolpidem Tartrate by Microdialysis-HPLC

The evaluation of the dissolution profile of hypnotic drugs is important to promote switching from original products to generic products by removing distrust in generic hypnotics. In this study, we investigated differences in the dissolution profiles between original and generic products (GE-D, GE-S, and GE-T) in commercially available zolpidem tartrate (ZOL) products using the HPLC method using a connected microdialysis probe (microdialysis-HPLC method). Although the degree of hardness and the disintegration time were not different among the original, GE-S, and GE-T, GE-D was 1.4 times harder than the other products. The disintegration time of GE-D was approximately twice as long as that of the original product. Generic products dissolved rapidly as compared with the original product, however, the dissolution rate in the ZOL powder (milled ZOL product) was not different between the original and generic products. Macrogol 6000 (polyethylene glycol (PEG)-6000) was used in the generic products, and this additive was the only PEG difference from the original product. We investigated whether the PEG in the product affected the solubility of ZOL and found that the addition of PEG-4000 or PEG-6000 significantly increased the dissolution rate. These results suggest that the solubility of ZOL may be increased by PEG when the product is disintegrated, resulting in the increased dissolution rate in the generic products. In conclusion, we found that the difference of PEG affected the dissolution profile in the disintegration process using the microdialysis-HPLC method. This finding can help ensure the safety of milled products and the selection of additives.

Submicron Matrices Embedded in a Polymeric Caplet for Extended Intravaginal Delivery of Zidovudine

In this study, an intravaginal delivery system able to deliver an anti-HIV-1 agent for the purpose of potentially reducing HIV-1 transmission acting over an extended duration was successfully formulated. This delivery system was a composite polymeric caplet comprising zidovudine-loaded polyethylene glycol enclatherated pectin-mucin submicron matrices embedded within a poly (D,L-lactide), magnesium stearate, Kollidon® SR, and Carbopol® 974P NF-based polymeric caplet matrix. A three-factor and three-level Box-Behnken statistical design was utilized to optimize the polymeric caplet. The optimized directly compressed composite polymeric caplet hardness was 22.1 ± 0.3 N and the matrix resilience was 62.4 ± 0.6%. The swelling- and diffusion-controlled fractional zidovudine (AZT) release from the optimized caplet was 0.74 ± 0.01 in simulated vaginal fluid (SVF), which increased to 0.81 ± 0.21 in phosphate-buffered saline (PBS) simulating seminal fluid, over 30 days. Caplet matrix swelling was directly related to the percentage Carbopol 974P NF composition. An intravaginal system for AZT delivery was tested in the pig model over 28 days. X-ray analysis depicted delivery system swelling with matrix contrast fading over time as vaginal fluid permeated the matrix core. Plasma, vaginal fluid swab eluates, and tissue AZT concentrations were measured by gradient ultra-performance liquid chromatography (UPLC)-tandem photodiode array detection. Vaginal tissue and vaginal fluid swab eluate AZT concentrations remained above effective levels over 28 days and were higher than plasma AZT concentrations, availing a system with reduced systemic toxicity and more effective inhibition of viral replication at the site of entry.

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.

Glycerin fatty acid esters as a new lubricant of tablets

Lubrication properties were compared among glycerin fatty acid esters (Poem TR-FB and Poem TR-HB), magnesium stearate (Mg-St), and a sucrose fatty acid ester (RYOTO SUGAR ESTER S-370F: SSE). Granules containing 50% acetaminophen were prepared, and improvements in their fluidity by the lubricants were compared. The lubricant effects of TR-FB and HB during tablet punching (pressure transmission ratio, ejection force) were similar to those of Mg-St and were better than those of SSE. When the lubricant content, mixing time, and tabletting pressure were changed, TR-FB and TR-HB provided better tablet hardness than Mg-St. TR-FB and TR-HB made tablets more disintegratable than Mg-St. When the effects of these lubricants on the stability of acetylsalicylic acid (ASA) were compared, Mg-St promoted its hydrolysis, but TR-FB or TR-HB did not affect its stability.