Effects of storage humidity on the mechanical, microstructural, and drug release properties of hydroxypropylmethylcellulose-based hydrophilic matrix tablets

The effects of storage humidity on the properties of hydroxypropylmethylcellulose (HPMC)-based hydrophilic matrix tablets were investigated. Hydrochlorothiazide tablets prepared with HPMCs of different thickening capacities were stored for 6 months (a) at a relative humidity corresponding to the prestorage equilibrium moisture content of the HPMCs, or (b) at a higher relative humidity. Only tablets stored at the higher humidity showed significant changes in properties, indicating that the observed changes (reduced crushing strength, increased total porosity, and increased mean pore diameter) were due to water uptake. All changes were completed within I month of storage. Drug release properties were unaffected, even after 6 months. Effectively identical results were obtained regardless of whether the HPMC variety used had a nominal viscosity of 4,000 cP or 100,000 cP.