Examination of the compaction properties of a 1:1 acetaminophen:microcrystalline cellulose mixture using precompression and main compression

Formulation and process strategies to minimize coat damage for compaction of coated pellets in a rotary tablet press: A mechanistic view

Compaction of multiple-unit pellet system (MUPS) tablets has been extensively studied in the past few decades but with marginal success. This study aims to investigate the formulation and process strategies for minimizing pellet coat damage caused by compaction and elucidate the mechanism of damage sustained during the preparation of MUPS tablets in a rotary tablet press. Blends containing ethylcellulose-coated pellets and cushioning agent (spray dried aggregates of micronized lactose and mannitol), were compacted into MUPS tablets in a rotary tablet press. The effects of compaction pressure and dwell time on the physicomechanical properties of resultant MUPS tablets and extent of pellet coat damage were systematically examined. The coated pellets from various locations at the axial and radial peripheral surfaces and core of the MUPS tablets were excavated and assessed for their coat damage individually. Interestingly, for a MUPS tablet formulation which consolidates by plastic deformation, the tablet mechanical strength could be enhanced without exacerbating pellet coat damage by extending the dwell time in the compaction cycle during rotary tableting. However, the increase in compaction pressure led to faster drug release rate. The location of the coated pellets in the MUPS tablet also contributed to the extent of their coat damage, possibly due to uneven force distribution within the compact. To ensure viability of pellet coat integrity, the formation of a continuous percolating network of cushioning agent is critical and the applied compaction pressure should be less than the pellet crushing strength.

Influence of the punch diameter and curvature on the yield pressure of MCC-compacts during Heckel analysis

The volume reduction behaviour of powders has been quantified by means of the 'in-die' yield pressure (YP) using Heckel analysis. However, because different YPs are reported for the same material, the experimental conditions influencing this material-constant were investigated. Silicified microcrystalline cellulose was compressed into flat-faced and convex tablets using a compaction simulator instrumented with load and displacement transducers. During compression, upper and lower punch force and displacement data were recorded and corrected for punch deformation. A symmetrical triangle wave compression profile was used and the instantaneous punch velocity was kept constant (5mm/s). Individual tablet height and weight were used for Heckel analysis. The influence of the 'effective compression pressure' (P(EFF)) (ranging from 10 to 350 MPa), punch diameter (PD) (4, 9.5 and 12 mm) and filling depth (FD) (4.5, 7.5 and 10.5mm) on YP was statistically evaluated using Response Surface Modelling software. A quadratic surface response equation, describing the relationship between P(EFF), PD, FD and YP, was proposed for concave (Adj R(2): 0.8424; S.D.: 14.60 MPa) and flat-faced (Adj R(2): 0.8409; S.D.: 4.49 MPa) punches. YP and tensile strength were mainly determined by P(EFF), irrespective of punch curvature. FD and PD had only a minor influence on the YP, although more pronounced for the concave punches. The method used resulted in reproducible P(EFF) and tensile strength values and the flat-faced tablets showed less weight variation. Flat-faced punches are preferred over punches with a concave surface when investigating the volume reduction behaviour of a powder by means of Heckel analysis and the experimental parameters should be reported.

The influence of varying precompaction and main compaction profile parameters on the mechanical strength of compacts

The purpose of this work was to investigate how altering the method of force application could be beneficial to tablet production in order to increase tablet strength and eliminate or minimize the incidence of capping and lamination. An integrated compaction research system (i.e., compaction simulator) was used throughout this study. Compaction profiles containing a single compaction event and a double (pre- and main) compaction event were created. The ratio and magnitude of the pre- and main compaction pressures were varied and the time interval between the pre- and main compaction events was altered to determine the effects on the crushing strengths and capping tendency of the final compacts. In all cases, for a given pressure, the double compaction event produced stronger tablets than the single compaction event. When the ratio and magnitude of the pre- and main compaction pressures were varied, the results differed depending on the material undergoing compaction. Dicalcium phosphate/microcrystalline cellulose and pregelatinized starch tablets had no significant difference in crushing strength values regardless of whether the precompaction pressure was less than or greater than the main compaction pressure. However, both direct compression (DC) acetaminophen and DC ibuprofen were found to have increased crushing strengths and decreased capping/lamination when the precompaction pressure was less than the main compaction pressure. When the time interval between the pre- and main compaction events was varied from 30 to 500 msec, no significant difference in the crushing strength or capping/lamination tendency was observed. It was concluded that the effect of altering the ratio and magnitude of the pre- and main compaction pressures varied from one material to another, suggesting that the profiles should be tailored individually for the specific material undergoing compaction.

The effects of lag-time and dwell-time on the compaction properties of 1:1 paracetamol/microcrystalline cellulose tablets prepared by pre-compression and main compression

The effects of lag-time and dwell-time on the compaction properties of tablets compressed from a 1:1 blend of paracetamol and microcrystalline cellulose have been examined using a compaction simulator. Increases in lag-times (from 0.06 to 0.53 s) resulted in small increases in the tensile strengths of the tablets when combinations of 80 and 160 MPa were used as the compression pressures. Further increases in lag-time did not alter the tablet strengths. When combinations of 240 and 320 MPa were used for pre-compression and main compression, the effects on the tensile strengths were more complex, partly because the high elastic recoveries of the tablets resulted in greater variability in the data. Increases in lag-times from 0.06 to 0.97 s resulted in an increase of between 12 and 28% in tensile strength. Longer lag-times (1.24 or 1.52 s) did not result in further increases in tensile strength. The application of a dwell-time of 0.26 s during pre-compression or main compression pressures of 80 and 160 MPa generally led to a decrease (14-22%) in tensile strength compared with tablets where no dwell-time was used. This was because of increases in both the elastic recoveries and elastic energies. Subsequent increases in dwell-time from 0.26 to 0.9 s resulted in increases in tablet strength compared with that obtained when no dwell-time was applied. The tensile strengths of tablets made with a pre-compression of 160 MPa then a main compression of 80 MPa were 11-33% higher than those of tablets made with a pre-compression of 80 MPa then a main compression of 160 MPa. This was because higher plastic energies and more plastic deformation occurred at the higher pre-compression. Generally, the application of dwell-time resulted in greater increases in tensile strengths than lag-time, which had less effect on the compaction properties.

Effect of compression speeds on the compaction properties of a 1:1 paracetamol-microcrystalline cellulose mixture prepared by single compression and by combinations of pre-compression and main-compression

A 1:1 blend of paracetamol and microcrystalline cellulose was compacted at different compression speeds by single compression or combinations of pre- and main-compression. The tensile strengths of the tablets decreased from 0.74+/-0.01 to 0.44+/-0.05 MPa as the compression speed was increased from 78 to 390 mm/s when a single compression pressure of 80 MPa was used to compress the tablets. When combinations of pre- and main-compression of 320 and 240 MPa were used to compress the tablets, tensile strengths decreased from 3.12+/-0.67 MPa at a compression speed of 78 mm/s to 1.24+/-0.36 MPa when the compression speed was 390 mm/s. The energies of compression and the ratio of elastic to plastic energies increased with increase in compression speed. This was because the material was becoming more elastic and more energy was required for the elastic expansion leading to a reduction in the energy available for plastic deformation and bond formation which resulted in a decrease in tensile strengths. Pre-compression played a major role at high compression speeds. The tensile strengths of tablets (1.2+/-0.08 MPa) compressed with a pre-compression of 160 MPa followed by a main-compression of 80 MPa (compression speed of 390 mm/s) were similar to the tensile strengths of tablets (1.1+/-0.10 MPa) compressed using a single compression of 320 MPa at the same compression speed of 390 mm/s. Thus, combinations of lower pressures can be employed to compress the material to the same tensile strength as a high single compression.