Characterization of a novel hydroxypropyl methylcellulose (HPMC) direct compression grade excipient for pharmaceutical tablets

Controlled release tablets are important dosage forms enabling a slower release of the drug and better pharmacokinetics for some drugs and hydrophilic matrix tablets utilizing hydroxypropyl methylcellulose (HPMC) are one of the most common types. One of the main challenges with using HPMC is its poor flow when implemented in a direct compression process or when utilized for continuous manufacturing for which novel grades of direct compression have been developed. In this work, three different direct compression (DC) grades of HPMC (K4M, K15M and K100M) were characterized and compared to their standard grade (CR) counterparts. These materials were compared in terms of density, particle size, morphology, surface area and powder flow using multiple techniques. Results showed that the materials were almost identical in terms of particle shape and although the DC grades had better flow, the particle size was slightly smaller with an unexpectedly higher surface area, which most likely resulted from the inclusion of co-processed silicon dioxide in the DC grades. The bulk, tapped and true densities were slightly higher for all of the DC grades. Of the eleven different parameters used to characterize the flow of the materials the DC grades showed better flow than their standard CR counterparts for nine of the parameters (Carr's Index, Erweka flow, FT4 Flow Rate Index, Mean Avalanche Time, Avalanche Scatter, Number of Avalanches, Shear Cell Uni-axial Compressive Strength and Shear Cell Flow Function Coefficient). Only the FT4 Basic Flowability Energy and Specific Energy showed the opposite trend which can be explained from the testing methodology. It is recommended to evaluate the DC grades of HPMC for processes where better flowing material would have an advantage, such as direct compression, continuous manufacturing, and roller compaction if the powder flow into the rolls is problematic.