Effect of hydroxypropyl cellulose (HPC) on dissolution rate of hydrochlorothiazide tablets

Hydrochlorothiazide (HCTZ) 60 mg strength tablets containing commonly used excipients and hydroxypropyl cellulose, marketed as either Klucel-EF (HPC, NF from Hercules, USA) or HPC-L (HPC, NF from Nippon Soda, Japan), as a binder were manufactured using identical aqueous wet granulation process. The tablets containing Klucel-EF as a binder exhibited higher dissolution rates than those manufactured using HPC-L. The granulations containing Klucel-EF or HPC-L showed no significant differences in compressibility and compactibility based on analysis performed using the Instron-Stress–Strain Analyzer. Both HPC grades met NF specifications and there were no differences for the NF test results in the certificates of analysis by their respective vendors. Further evaluation of both HPC grades indicated that the cloud point values for Klucel-EF and HPC-L in water were 39(±1) and 48 °C, respectively. The differences in cloud points of Klucel-EF and HPC-L were correlated to the differences in the percent hydroxypropoxy content and the degree of molecular substitution, which were higher for Klucel-EF than for HPC-L. These structural features make Klucel-EF less hydrophilic. Since the cloud point of Klucel-EF was similar to the dissolution medium temperature of 37(±2) °C, it may present a less viscous layer surrounding the HCTZ granules enabling faster dissolution of the drug.