Microstructure of Tablet—Pharmaceutical Significance, Assessment, and Engineering

Purpose: To summarize the microstructure – property relationship of pharmaceutical tablets and approaches to improve tablet properties through tablet microstructure engineering. Method: The main topics reviewed here include: 1) influence of material properties and manufacturing process parameters on the evolution of tablet microstructure; 2) impact of tablet structure on tablet properties; 3) assessment of tablet microstructure; 4) development and engineering of tablet microstructure. Results: Microstructure plays a decisive role on important pharmaceutical properties of a tablet, such as disintegration, drug release, and mechanical strength. Useful information on mechanical properties of a powder can be obtained from analyzing tablet porosity—pressure data. When helium pycnometry fails to accurately measure true density of a water-containing powder, non-linear regression of tablet density—pressure data is a useful alternative method. A component that is more uniformly distributed in a tablet generally exerts more influence on the overall tablet properties. Conclusion: During formulation development, it is highly recommended to examine the relationship between any property of interest and tablet porosity when possible. Tablet microstructure can be engineered by judicious selection of formulation composition, including the use of the optimum solid form of the drug and appropriate type and amount of excipients, and controlling manufacturing process.