Pharmaceutical tableting remains a crucial process in the production of oral solid dosage forms. Despite advancements in formulation science and machinery, recurring challenges such as low tablet hardness, weight variation, and capping continue to compromise quality, compliance, and patient safety. These issues are not only process-related but also reflect more complex interactions between formulation components and material properties.
Tablet hardness is a critical quality attribute (CQA) that influences product durability, packaging integrity, and dissolution behavior. Hardness is governed by interparticulate bonding strength, compression force, and the deformation properties of excipients.
Insufficient compaction force or dwell time [1]
Poor cohesion, improper binder, or low binder concentration
Optimize compression parameters
Use plastically deforming fillers like microcrystalline cellulose (MCC). Integrate or increase the binder concentration to enhance the particle cohesion and so the tablet's mechanical strength. Typical binders such as polyvinylpyrrolidone (PVP) or cellulose-based binders like hydroxypropylcellulose (HPC) or low-viscosity Hypromellose (PHARMACOAT®/TYLOPUR®), can be used in both granulation processes and direct compression. [2-3]
Tablet weight variation directly affects dosage accuracy and patient safety. Regulatory limits, such as those defined in USP <905> Uniformity of Dosage Units, require that tablet mass falls within a specified range of the target weight.
Non-uniform powder flow or segregation [4]
Poor die fill control, especially at high turret speeds, malfunctioning feeders, or misaligned tooling [5]
Improve powder flow by the addition of flow agents (e.g., colloidal silicon dioxide) or through granulation processes using binders to ensure adequate granule size.
Capping refers to the partial or complete separation of the top or bottom part of a tablet. It results from air entrapment, excessive elasticity, or inadequate bonding. Lamination involves horizontal splitting of a tablet into distinct layers.
Rapid decompression leading to elastic rebound [6]
Inadequate pre-compression or lack of dwell time
Dry granules with low moisture content or poor plasticity
Use pre-compression to reduce air entrapment [7]
Maintain optimal moisture in granules (typically 1–2% w/w for most excipients) Improve granule plasticity through binder optimization. Typically, PVP or fine grades of HPC having an optimized surface area improve the cohesion of the tablet's components. Its binding action prevents the formation of air pockets, creating a more compact and uniform tablet. Another excipient solving capping and lamination issues is low-substituted L-HPC, especially LH-11. Its elongated, interlocking fibers enhance mechanical interparticulate bonding and reduce ejection stresses during the compression.
Persistent tableting defects—low hardness, weight variation, and capping—reflect the complex interactions between material properties, formulation design, and process parameters. Addressing these challenges requires a deep understanding of powder characterization, compaction science, and equipment optimization. To do so, implementing an integrated Quality by Design (QbD) approach and control strategies provides a better understanding of the formulation design/production window and ensures reliable product quality and compliance.
[1] ICH Q8 (R2): Pharmaceutical Development
[2] Aulton, M. E. & Taylor, K. (2017). Aulton's Pharmaceutics: The Design and Manufacture of Medicines, 5th Ed.
[3] Rowe, R. C., Sheskey, P. J., & Quinn, M. E. (2009). Handbook of Pharmaceutical Excipients
[4] USP <905>: Uniformity of Dosage Units
[5] Hoag, S. W. (2011). Pharmaceutical Dosage Forms: Tablets, Vol. 1
[6] Lieberman, H. A., Lachman, L., & Schwartz, J. B. (1990). Pharmaceutical Dosage Forms: Tablets, Vol. 2
[7] EMEA: Guideline on the Manufacture of the Finished Dosage Form (CPMP/QWP/486/95)
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