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Thio DR, Ong YM, Veronica N, Heng PWS, Chan LW. Native starch derived from different botanical sources as an effective co-cushioning agent in MUPS tablets. Int J Pharm 2025; 670:125131. [PMID: 39725092 DOI: 10.1016/j.ijpharm.2024.125131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2024] [Revised: 12/08/2024] [Accepted: 12/22/2024] [Indexed: 12/28/2024]
Abstract
Compaction of sustained release coated pellets into multi-unit pellet system (MUPS) tablets has been associated with damage to the functional polymer layer, leading to a loss in desired sustained release function. Many filler materials and complex processes have been studied on their ability to mitigate compaction-induced pellet coat damage. Among these, native or unprocessed starches included in the filler material have not been explored well despite being a simple strategy. Sustained release pellets with ethylcellulose or acrylic coats were compacted into MUPS tablets with different filler materials, containing microcrystalline cellulose and native starch at 25 %, w/w or 40 %, w/w derived from rice, tapioca, corn, or potato. The MUPS tablet tensile strength and the extent of pellet coat damage were evaluated. Although starch weakened the tablets, rice and tapioca starch significantly mitigated pellet coat damage the most by 10 - 44 % (p < 0.008). Higher starch concentrations and higher compaction pressures led to a greater cushioning effect, which was indicated to result from reduced plastic deformation and increased particle rearrangement of the filler material. Pellets coated with acrylic benefitted more from starch and experienced less coat damage than pellets with ethylcellulose coats. This research demonstrates the use of native starches as a simple method to mitigate pellet coat damage in MUPS tablets.
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Affiliation(s)
- Daniel Robin Thio
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy and Pharmaceutical Sciences, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Yu Min Ong
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy and Pharmaceutical Sciences, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Natalia Veronica
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy and Pharmaceutical Sciences, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Paul Wan Sia Heng
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy and Pharmaceutical Sciences, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Lai Wah Chan
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy and Pharmaceutical Sciences, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
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2
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Hiew TN. Dr. Paul W. S. Heng, a guru in pharmaceutical processing research. Int J Pharm 2024; 666:124816. [PMID: 39389476 DOI: 10.1016/j.ijpharm.2024.124816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/12/2024]
Affiliation(s)
- Tze Ning Hiew
- Department of Pharmaceutical Sciences and Experimental Therapeutics, College of Pharmacy, The University of Iowa, Iowa City, Iowa 52242, United States.
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3
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Wu S, Zhou G, Wang X, Zhang X, Guo S, Ma Y, Liu H, Li W. Development of Sinomenine Hydrochloride Sustained-release Pellet With Multiple Release Characteristics. AAPS PharmSciTech 2024; 25:224. [PMID: 39322795 DOI: 10.1208/s12249-024-02949-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2024] [Accepted: 09/16/2024] [Indexed: 09/27/2024] Open
Abstract
Due to the gastrointestinal side effects, the clinical application of sinomenine hydrochloride (SH) in rheumatoid arthritis is limited. The elderly population constitutes the primary group affected by this disease, and within this demographic, there are significant variations in gastric emptying time. To reduce the influence of individual differences on drug efficacy and concurrently alleviate gastrointestinal side effects, the SH sustained-release pellets with multiple release characteristics were developed, which comprised both regular sustained-release pellets and enteric-coated sustained-release pellets. The drug-loaded layer formulation was optimized by full factorial design. With the optimal formulation, the drug-loaded pellets achieved a yield of 96.05%, an encapsulation efficiency of 83.36% for SH, a relative standard deviation of 3.26% in SH content distribution, an average roundness of 0.971 for the pellets, and the particle size span of 0.808. The pellets with a 4 h SH release profile in an acidic environment and pellets displaying 4 h acid resistance followed by an 8 h SH release behavior in the intestinal environment were individually prepared through in vitro dissolution tests. The results demonstrated stable and compliant dissolution behavior of the formulation, along with excellent stability and physical appearance. This research offers novel insights and references for the innovative formulation of SH.
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Affiliation(s)
- Sijun Wu
- College of Pharmaceutical Engineering of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Guoming Zhou
- College of Pharmaceutical Engineering of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Xi Wang
- College of Pharmaceutical Engineering of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Xiaoyang Zhang
- College of Pharmaceutical Engineering of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Shubo Guo
- College of Pharmaceutical Engineering of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China
| | - Yongqiang Ma
- Xinyite Science and Technology Co., Ltd, Guangdong, 518083, China
| | - Hai Liu
- Xinyite Science and Technology Co., Ltd, Guangdong, 518083, China
| | - Wenlong Li
- College of Pharmaceutical Engineering of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, China.
- Haihe Laboratory of Modern Chinese Medicine, Tianjin, 301617, China.
- Tianjin Key Laboratory of Intelligent and Green Pharmaceuticals for Traditional Chinese Medicine, Tianjin, 301617, China.
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4
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Paulausks A, Kolisnyk T, Mohylyuk V. The Increase in the Plasticity of Microcrystalline Cellulose Spheres' When Loaded with a Plasticizer. Pharmaceutics 2024; 16:945. [PMID: 39065642 PMCID: PMC11279479 DOI: 10.3390/pharmaceutics16070945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2024] [Revised: 07/10/2024] [Accepted: 07/11/2024] [Indexed: 07/28/2024] Open
Abstract
Compaction pressure can induce an undesirable solid-state polymorphic transition in drugs, fragmentation, loss of coated pellet integrity, and the decreased viability and vitality of microorganisms. Thus, the excipients with increased plasticity can be considered as an option to decrease the undesirable effects of compaction pressure. This study aims to increase the plasticity (to reduce the mean yield pressure; Py) of dried microcrystalline cellulose (MCC) by loading it with a specially selected plasticizer. Diethyl citrate (DEC), water, and glycerol were the considered plasticizers. Computation of solubility parameters was used to predict the miscibility of MCC with plasticizers (possible plasticization effect). Plasticizer-loaded MCC spheres with 5.0 wt.% of water, 5.2 wt.% of DEC, and 4.2 wt.% glycerol were obtained via the solvent method, followed by solvent evaporation. Plasticizer-loaded formulations were characterised by TGA, DSC, pXRD, FTIR, pressure-displacement profiles, and in-die Heckel plots. Py was derived from the in-die Heckel analysis and was used as a plasticity parameter. In comparison with non-plasticized MCC (Py = 136.5 MPa), the plasticity of plasticizer-loaded formulations increased (and Py decreased) from DEC (124.7 MPa) to water (106.6 MPa) and glycerol (99.9 MPa), and that was in full accordance with the predicted miscibility likeliness order based on solubility parameters. Therefore, water and glycerol were able to decrease the Py of non-plasticized MCC spheres by 16.3 and 30.0%, respectively. This feasibility study showed the possibility of modifying the plasticity of MCC by loading it with a specially selected plasticizer.
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Affiliation(s)
- Artūrs Paulausks
- Leading Research Group, Faculty of Pharmacy, Riga Stradiņš University, 21 Konsula Str., LV-1007 Riga, Latvia
| | - Tetiana Kolisnyk
- School of Pharmacy, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland, UK
- Department of Industrial Technology of Drugs, National University of Pharmacy, 53 Pushkins’ka Str., 61002 Kharkiv, Ukraine
| | - Valentyn Mohylyuk
- Leading Research Group, Faculty of Pharmacy, Riga Stradiņš University, 21 Konsula Str., LV-1007 Riga, Latvia
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Alshora D, Alyousef W, Ibrahim M. Effects of Functional Biomaterials on the Attributes of Orally Disintegrating Tablets Loaded with Furosemide Nanoparticles: In Vitro and In Vivo Evaluations. J Funct Biomater 2024; 15:161. [PMID: 38921534 PMCID: PMC11204571 DOI: 10.3390/jfb15060161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2024] [Revised: 06/03/2024] [Accepted: 06/06/2024] [Indexed: 06/27/2024] Open
Abstract
Furosemide (FUR) is a diuretic used to relieve edema, congestive heart failure, cirrhosis, end-stage renal disease, and hypertension. FUR is a class IV according to the Biopharmaceutics Classification System. It is practically insoluble in water. This study aimed to optimize and formulate porous orally disintegrating tablets (ODTs) prepared by sublimation and loaded with FUR nanoparticles prepared by using a planetary ball mill. Different functional biomaterials called stabilizers were used to stabilize the nanoparticle formula. Pluronic F-127 was the optimum stabilizer in terms of particle size (354.07 ± 6.44), zeta potential (-25.3 ± 5.65), and dissolution efficiency (56.34%). The impact of the stabilizer concentration was studied as well, and a concentration of 3% showed the smallest particle size (354.07 ± 6.44), best zeta potential value (-25.3 ± 5.65), and percentage of dissolution rate (56.34%). A FUR-loaded nanoparticle formula was successfully prepared. The nanoparticle formula was stabilized by using 3% pluronic F-127, and 3% was chosen for further study of the incorporation into oral disintegration tablets prepared by the sublimation technique. The impact of the matrix sublimating agent and superdisintegrant on the ODTs' attributes (in vitro disintegration, wetting time, and in vitro dissolution efficiency) was studied using 32 full factorial designs. In vivo, the diuretic activity was tested for the optimized FUR ODTs by calculating the Lipschitz value using rats as an animal model. The stability of the ODTs loaded with FUR nanoparticles was assessed under accelerated conditions for 6 months. Finally, the ODT formula loaded with FUR NPs showed a rapid onset of action that was significantly faster than untreated drugs. Nanonization and ODT formulation enhances the dissolution rate and bioavailability of FUR. Many factors can be controlled to achieve optimization results, including the formulation and process parameters.
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Affiliation(s)
- Doaa Alshora
- Department of Pharmaceutics, College of Pharmacy, King Saud University, P.O. Box 22452, Riyadh 11459, Saudi Arabia; (W.A.); (M.I.)
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Thio DR, Veronica N, Heng PWS, Chan LW. Tableting of coated multiparticulates: Influences of punch face configurations. Int J Pharm 2024; 653:123863. [PMID: 38307400 DOI: 10.1016/j.ijpharm.2024.123863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 01/17/2024] [Accepted: 01/25/2024] [Indexed: 02/04/2024]
Abstract
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.
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Affiliation(s)
- Daniel Robin Thio
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Natalia Veronica
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Paul Wan Sia Heng
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Lai Wah Chan
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
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7
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Moutaharrik S, Palugan L, Cerea M, Filippin I, Maroni A, Gazzaniga A, Foppoli A. Cushion-coated pellets for tableting without external excipients. Int J Pharm 2024; 653:123874. [PMID: 38316318 DOI: 10.1016/j.ijpharm.2024.123874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Revised: 01/30/2024] [Accepted: 01/31/2024] [Indexed: 02/07/2024]
Abstract
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.
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Affiliation(s)
- Saliha Moutaharrik
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy.
| | - Luca Palugan
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy
| | - Matteo Cerea
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy
| | - Ilaria Filippin
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy
| | - Alessandra Maroni
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy
| | - Andrea Gazzaniga
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy
| | - Anastasia Foppoli
- Università degli Studi di Milano, Dipartimento di Scienze Farmaceutiche, Sezione di Tecnologia e Legislazione Farmaceutiche "Maria Edvige Sangalli", via G. Colombo 71, 20133 Milano, Italy
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8
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Tian W, Li X, Li W, Xue A, Zheng M, Lin X, Hong Y. Influence of Extrudate-Based Textural Properties on Pellet Molding Quality. Pharmaceuticals (Basel) 2023; 16:1505. [PMID: 37895976 PMCID: PMC10610123 DOI: 10.3390/ph16101505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 10/16/2023] [Accepted: 10/20/2023] [Indexed: 10/29/2023] Open
Abstract
As the precursor of pellets, the extrudate has a direct impact on the molding quality of the pellets. Therefore, the correlation between the surface roughness of the extrudates and the molding quality of pellets with pure microcrystalline cellulose (MCC) formulations and those containing traditional Chinese medicine (TCM) formulations was explored. MCC was used as a pelleting agent, mixer torque rheometry (MTR) was used to guide the optimal dosage of the wetting agent, and TCM extracts (drug loadings of 20% to 40%) were selected as model drugs to prepare the extrudates and pellets under the same extrusion spheronization process conditions. The surface roughness and texture parameters of extrudates were analyzed via a microscope and texture analyzer, respectively, and the quality of pellets was evaluated. The extrudate roughness of the pure MCC prescription decreased and then increased with increasing water addition, while the extrudate roughness of the prescription containing TCM extracts tended to increase and then decrease. The addition of water affected the extrudate properties, with TCM extract molecules filling gaps in the MCC structure, leading to rough surfaces. The extrudate roughness of the TCM prescriptions was significantly greater than that of the pure MCC prescriptions at optimal water addition levels, resulting in ideal pellets.
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Affiliation(s)
- Wenxiu Tian
- Shanghai Innovation Center of TCM Health Service, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China; (W.T.); (X.L.); (W.L.); (A.X.); (M.Z.)
| | - Xue Li
- Shanghai Innovation Center of TCM Health Service, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China; (W.T.); (X.L.); (W.L.); (A.X.); (M.Z.)
| | - Wenjie Li
- Shanghai Innovation Center of TCM Health Service, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China; (W.T.); (X.L.); (W.L.); (A.X.); (M.Z.)
| | - Aile Xue
- Shanghai Innovation Center of TCM Health Service, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China; (W.T.); (X.L.); (W.L.); (A.X.); (M.Z.)
| | - Minyue Zheng
- Shanghai Innovation Center of TCM Health Service, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China; (W.T.); (X.L.); (W.L.); (A.X.); (M.Z.)
| | - Xiao Lin
- College of Chinese Materia Medica, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China
| | - Yanlong Hong
- Shanghai Innovation Center of TCM Health Service, Shanghai University of Traditional Chinese Medicine, No. 1200, Cai-Lun Road, Pudong District, Shanghai 201203, China; (W.T.); (X.L.); (W.L.); (A.X.); (M.Z.)
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9
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Thio DR, Aguilera Q, Yeoh JKX, Sia Heng PW, Chan LW. An evaluation of microcrystalline cellulose attributes affecting compaction-induced pellet coat damage through a multi-faceted analysis. Int J Pharm 2023; 643:123245. [PMID: 37467819 DOI: 10.1016/j.ijpharm.2023.123245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 06/21/2023] [Accepted: 07/16/2023] [Indexed: 07/21/2023]
Abstract
Pellet coat damage in multi-unit pellet system (MUPS) tablets has previously been studied and addressed with limited success. The effects of lactose filler material attributes on pellet coat damage have been relatively well-studied but a similar understanding of microcrystalline cellulose (MCC) is lacking notwithstanding its high cushioning potential. Hence, the relationships between MCC attributes and pellet coat damage were investigated. Single pellet in minitablets (SPIMs) were used to isolate pellet-filler effects and reveal the under-unexplored impact of risk factors found in MUPS tablets. MUPS tablets and SPIMs were prepared with various grades of MCC and pellets with an ethylcellulose or acrylic coat at various compaction pressures. Subsequently, the extent of pellet coat damage was determined by dissolution test and quantified using two indicators to differentiate the nature of the damage. A multi-faceted analytical approach incorporated linear regression, correlations and a classification and regression tree algorithm and evaluated how MCC attributes, such as flowability, particle size and plastic deformability, exert various influences on the extent of ethylcellulose and acrylic pellet coat damage. This analysis improved the understanding of the different mechanisms by which pellet coat damage to these two polymer types occurs which can help enhance future pellet coat damage mitigation strategies.
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Affiliation(s)
- Daniel Robin Thio
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Quinton Aguilera
- Department of Civil, Environmental and Geomatic Engineering, University College London, London WC1E 6DE, UK
| | - Janice Ke Xin Yeoh
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Paul Wan Sia Heng
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Lai Wah Chan
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
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