Bead compacts. I. Effect of compression on maintenance of polymer coat integrity in multilayered bead formulations

Tableting of coated multiparticulates: Influences of punch face configurations

The influences of the punch face design on multi-unit pellet system (MUPS) tablets were investigated. Drug-loaded pellets coated with sustained release polymer based on ethylcellulose or acrylic were compacted into MUPS tablets. Punch face designs used include standard concave, deep concave, flat-faced bevel edge and flat-faced radius edge. MUPS tablets compacted at 2 or 8 kN were characterized for their tensile strength. The extent of pellet coat damage after tableting was evaluated from drug release profiles. Biconvex tablets were weaker by 0.01-0.15 MPa, depending on the pellet type used, and had 1-17 % higher elastic recovery (p < 0.000) than flat-faced tablets. At higher compaction force, the use of the deep concave punch showed a 13-26 % lower extent of pellet coat damage, indicated by a relatively higher mean dissolution time, compared to other punch face configurations (p < 0.000). This was attributed to increased rearrangement energy of the compacted material due to the high punch concavity, which sequestered compaction stress exerted on pellet coats. Although the deep concave punch reduced the stress, the resultant tablets containing pellets coated with acrylic were weaker (p = 0.01). Overall, the punch face configuration significantly affected the quality of MUPS tablets.

Cushion-coated pellets for tableting without external excipients

Multiple-unit dosage forms prepared by compacting pellets offer important manufacturing and compliance advantages over pellet-filled capsules. However, compaction may negatively affect the release control mechanism of pellets, and subunits may not be readily available after intake. Application of a cushioning layer to the starting units is here proposed as a strategy to obtain tablets with satisfactory mechanical strength, rapid disintegration and maintenance of the expected release profile of individual subunits while avoiding the use of mixtures of pellets and excipients to promote compaction and limit the impact of the forces involved. Cushion-coating with PEG1500, a soft and soluble material, was proved feasible provided that the processing temperature was adequately controlled. Cushioned gastro-resistant pellets were shown to consolidate under relatively low compaction pressures, which preserved their inherent release performance after tablet disintegration. Adhesion problems associated with the use of PEG1500 were overcome by applying an outer Kollicoat® IR film. Through design of experiment (DoE), robustness of the proposed approach was demonstrated, and the formulation as well as tableting conditions were optimized. The tableted cushion-coated pellet systems manufactured would allow a relatively high load of modified-release units to be conveyed, thus setting out a versatile and scalable approach to oral administration of multiple-unit dosage forms.

Cushioning pellets based on microcrystalline cellulose - Crospovidone blends for MUPS tableting

Compaction of multiple-unit pellet system (MUPS) tablets has been extensively reported to be potentially challenging. Thus, there is a need for non-segregating cushioning agents to mitigate the deleterious effect of the compaction forces. This study was designed to investigate the use of porous pellets as cushioning agents using different drying techniques to prepare pellets of various porosities and of different formulations. The pellets fabricated were characterized for their porosity and crushing strength. Subsequently, MUPS tablets were prepared using blends of polymer-coated pellets and custom-designed cushioning pellets by compacting at different pressures. The effects of pellet volume fraction and dwell time on the pellet coat damage, as well as the tensile strength of the resultant MUPS tablets were also investigated. Compacts with coated pellet volume fraction of 0.21 exhibited the best cushioning effect when tableted at different compression speeds with both gravity and force feeders. The findings from this study showed that cushioning pellet porosity was highest when drying was carried out by freeze drying, followed by fluid bed drying and oven drying. There was an inverse relationship between cushioning pellet porosity and strength. The tensile strength of tablets prepared from freeze dried pellets was highest. The protective effect of the cushioning pellets was principally dependent on their porosity. Also, pellet volume fraction in the compacts and compaction pressure used had remarkable effect on pellet coat damage. When unprocessed powders were compacted by automatic die filling, capping and lamination problems were observed. However, tablets of reasonable quality were made with the cushioning pellets. Freeze dried pellets containing crospovidone were found to be promising as cushioning agents and had enabled the production of MUPS tablets even at higher compaction pressures, beyond the intrinsic crushing strength of the coated pellets.

Influence of the porosity of cushioning excipients on the compaction of coated multi-particulates

The compaction of multiple unit-pellet system (MUPS) tablets poses considerable challenges due to potential compaction-induced damage to the functional polymer coat and segregation of pellets from other excipients during the tableting process. This study was designed to investigate the impact of porous pellets as cushioning agent without issues related to segregation while tableting. Different drying techniques were applied to produce microcrystalline cellulose (MCC) pellets with various porosities. Sodium chloride was also added to the pellet formulation as a pore forming agent to generate a porous skeleton after production and aqueous extraction. The pellets fabricated were characterized for their porosity, crushing strength and yield pressure. Tablets were prepared using unlubricated pellets and their tensile strengths determined. Blends containing polymer-coated pellets and cushioning pellets of various porosities were compacted at different compaction pressures. The porous pellets exhibiting the best cushioning effect were used for MUPS tableting at different compression speeds with both gravity and force feeders. The findings from this study showed that pellet porosity was highest when drying was carried out in a freeze dryer, followed by fluid bed and least porous from the oven. There was an inverse relationship between pellet porosity and strength. The protective effect of cushioning pellets was mainly dependent on their porosity. The porosity of pellets manufactured by leaching NaCl from MCC-NaCl (1:1) pellets were 2.14-, 2.57- and 4.88-fold higher than that of MCC PH101 only pellets for oven, fluid bed and freeze dried pellets, respectively. Although the porosity of MCC PH101-NaCl (1:3) pellets was highest, they exhibited less cushioning effect than MCC PH101-NaCl (1:1). It was inferred that a good balance between porosity and bulk density of cushioning pellets was essential to be effective at protecting the coated pellets from damage during compaction. Compared with MUPS tablets prepared using unprocessed MCC PH105, the tablets prepared with the porous freeze dried MCC PH101 (NaCl fraction leached) pellets had improved drug content uniformity and were mechanically stronger.

A mechanistic understanding of compression damage to the dissolubility of coated pellets in tablets

Damage to the drug diffusion coat barrier of controlled release pellets by the compaction force when preparing multiple-unit pellet system tablets is a major concern. Previous studies have shown that pellets located at the tablet axial and radial peripheral surfaces were more susceptible to damage when compacted due to the considerable shear encountered at these locations. Hence, this study was designed to assess with precision the impact of pellet spatial position in the compact on the extent of coat damage by the compaction force via a single pellet in minitablet (SPIM) system. Microcrystalline cellulose (MCC) pellet cores were consecutively coated with a drug layer followed by a sustained release layer. Chlorpheniramine maleate was the model drug used. Using a compaction simulator, the coated pellets were compacted singly into 3 mm diameter SPIMs with MCC as the filler. SPIMs with individual pellets placed in seven positions were prepared. The uncompacted and compacted coated pellets, as SPIMs, were subjected to drug release testing. The dissolution results showed that pellets placed at the top-radial position were the most susceptible to coat damage by the compaction force, while pellets positioned within the minitablet at the middle and upper quadrant positions showed the least damage. The SPIM system was found to be effective at defining the extent of coat damage to the pellet spatial position in the compact. This study confirmed that coated pellets located at the periphery were more susceptible to damage by compaction, with pellets located at the top-radial position showing the greatest extent of coat damage. However, if the pellet was completely encrusted by the cushioning filler, coat damage could be mitigated. Further investigations were directed at how the extent of coat damage impacted drug release. Interestingly, small punctures were found to be most detrimental to drug release whilst coats with large surface cuts did not completely fail. A damaged pellet coat has some self-sealing ability and failure is not total. Thus, this study provides a deeper understanding of the consequence of coat damage to drug release when sustained release coated pellets are breached.

Water-insoluble polymers as binders for pellet drug layering: Effect on drug release and performance upon compression

The objective of this study was to investigate the applicability of water-insoluble polymers as binders for pellet drug layering to extend the drug release. Carbamazepine was layered on sugar cores in fluidized bed coater using isopropanol (IPA):water solution or aqueous dispersion of ethylcellulose, polyvinyl acetate or ammonium-methylmethacrylate copolymer. Carbamazepine release was extended with all investigated water-insoluble polymers used as binder, without an additional coating layer. Drug release from pellets layered using IPA:water polymer solutions was dependent on polymer properties such as lipophilicity and pore-forming components, while from those layered with aqueous polymer dispersions, the release was dependent on the completeness of film formation during drug layering. Curing effect was observed only for pellets layered with Aquacoat® ECD and Eudragit® RS 30D. The drug release was not affected by compression when pellets were prepared with the flexible polymers Kollidon® SR or Kollicoat® SR 30D, however, it increased when brittle polymers such as ethylcellulose or Eudragit® RS were used. This problem could be minimized by using a higher amount of the binder, addition of a plasticizer or using polymers of higher viscosity grade. In conclusion, the use of water-insoluble polymers as binder for pellet drug layering is an effective tool to extend the drug release without additional coating step.

Internal structure and phase transition behavior of stimuli-responsive microgels in PEG melts

In this work we investigated the behaviour of stimuli-responsive poly(N-vinylcaprolactam) (PVCL) microgels in poly(ethylene glycol) (PEGs) with a linear architecture. We performed small-angle neutron scattering (SANS) experiments at two different microgel concentrations and various temperatures. The results were compared with those on PVCL microgels in water. PVCL in PEG (molecular weight M_W = 2 kg mol^-1) exhibits a volume phase transition temperature (VPTT) at a temperature between 160 and 180 °C. The diameter of the swollen microgel is only slightly smaller than in water. Furthermore, with increasing molecular weight of the surrounding polymer matrices fewer chains penetrate the microgel particles. In agreement with that, we identify a decreasing diameter with increasing molecular weight. In the short chain polymers up to M_W = 3 kg mol^-1, PVCL is well dispersed in the matrices with only minor signatures of agglomeration. For the well dispersed systems, we find unperturbed chain conformation of the PEG. Our results clearly show that the miscibility of PVCL and PEG disappears in a molecular weight range of 3 to 10 kg mol^-1.

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.

Investigation for the quality factors on the tablets containing medicated pellets

Sustained and controlled pellets are considered as one of the ideal dosage forms. Due to the large coverage area of pellets, loaded drugs can be absorbed completely in the body and bioavailability is improved correspondingly. Coated pellets-containing tablet is a special oral formulation consisting of various pellets with different release rate. Desired rate of drug release rate can be achieved by adjusting the proportion of pellets. However, this formulation faces strict requirements in the process of preparation. Several factors will influence release behavior of tablets, including pellet cores, coating, and tabletting. Therefore, these factors will be investigated sufficiently in this review to provide valuable information for manufacturing process.

Evaluation of Ceolus™ microcrystalline cellulose grades for the direct compression of enteric-coated pellets

The preparation of multiparticulate tablets by direct compression of functionally coated pellets is technologically challenging. The objective was to investigate the influence of different grades of microcrystalline cellulose (Ceolus™ UF-711, PH-102, PH-200 and KG-802) as fillers on the properties of blends and tablets containing enteric pellets. Celphere™ spheres were drug-layered and then functionally coated with Eudragit(®) L 30 D-55/FS 30D dispersion. Tablets loaded with 50% pellets were prepared using pure or binary blends of microcrystalline cellulose fillers. The influence of the filler on the blend flow, segregation tendency, tablet hardness and enteric release properties were studied using a mixture design, and the optimum filler composition was determined. Rapidly disintegrating tablets, which yielded a drug release of less than 10% after 2 hours in acidic medium, could be successfully prepared. The blend composition had a significant effect on the flowability, but less on the tablet hardness which was influenced by the selection of lubricant. Blends containing celluloses with low bulk densities exhibited a reduced tendency to segregate. Pellet distribution uniformity was further improved when using Ceolus™ UF-711 blended with a high-density grade. As a conclusion, multiparticulate tablets containing enteric pellets with preserved delayed-release properties were successfully prepared using Ceolus™ microcrystalline celluloses as tableting excipients. The optimized filler blend for the direct compression of 50% enteric pellets into tablets contained Ceolus™ UF-711 as main component in combination with Ceolus™ PH-200.

Performance of Multilayered Particles: Influence of a Thin Cushioning Layer

Nowadays, oral dosage forms with controlled release kinetics have known an increasing interest. The polymer coating of drug-loaded particles is one of the most common methods used for controlling drug delivery. Such multilayered particles could be either filled into capsules or compressed into tablets for their oral administration. However, many studies have noticed that coating films are damaged during the compression process, leading to significant changes in drug release profiles. The aims of this study were to investigate the effects of a thin cushioning layer [made of HydroxyPropylMethyl Cellulose (HPMC)] applied on coated theophylline particles upon particle characteristics, tablet properties, and then upon their dissolution performance. If no significant effect was shown with particles, this thin HPMC layer played an important role in the tablets. Tablet cohesiveness was decreased due to HPMC cushioning properties and moreover, the theophylline release rate was increased, as HPMC is a water-soluble polymer creating channels in polymer film for dissolution medium. Therefore, a cushioning layer helped to protect polymer coats from fracture during compression but could also affect drug release and so, both effects must be checked in such a drug delivery system.

Release of Diltiazem Hydrochloride from Hydrophilic Matrices of Polyethylene Oxide and Carbopol

The mucoadhesion, swelling, and drug release behavior of polyethylene oxide (PEO) and carbopol (CP) matrices were studied using a water soluble model drug diltiazem hydrochloride. The mucoadhesive strength of the matrices increased with increase in polymer content. The results showed that PEO was more mucoadhesive than CP. Mucoadhesion of the tablets was dependent upon the swelling. Swelling was ascertained by measuring the axial and radial expansion of matrix tablets following exposure to media of physiological ionic strength. There was a marked increase in the swelling index of matrices containing high polymer content of PEO as compared to CP. Drug release kinetics were found to be closely related to dissolution and swelling properties of the matrices. The release was found to be non-Fickian with n (release exponent) values ranging from 0.45-0.58. At a constant polymer content (15.84% w/w), the main contributing factor for the mucoadhesion, swelling, and release was the amount of PEO.

Bead compacts. II. Evaluation of rapidly disintegrating nonsegregating compressed bead formulations

In this study, three techniques for the prevention or mitigation of polymer coat fracture on compaction of sustained-release beads into tablets were investigated. All techniques in this paper were evaluated without the addition of any cushioning excipients, but rather by spray coating these excipients to avoid segregation during product manufacturing. First, it was shown that use of swellable polymers such as polyethylene oxide (PEO) serves a unique and effective role in preventing polymer coat rupture. PEO was spray coated between the ethylcellulose (EC) and microcrystalline cellulose (MCC) coats to evaluate its cushioning effect. The compacted PEO layered beads, on dissolution, disintegrated into individual beads with sustained drug release of up to 8 hr. It is postulated that the PEO was hydrated and formed a gel that acts as a sealant for the cracks formed in the ruptured polymer coating (sealant-effect compacts). Second, EC-coated drug-layered beads were also overcoated with cushioning excipients such as polyethylene glycol (PEG) and MCC with an additional coating of a disintegrant. These beads were compressed at pressures of 125, 500, and 1000 pounds into caplets and, on dissolution testing, disintegrated into individual beads when the dissolution medium was switched from simulated gastric to intestinal fluid. The dissolution profiles show that the polymer coat was partly disrupted on compaction, leading to a total drug release in 8-10 hr. Third, EC-coated beads were also granulated with cushioning excipient and compressed.