Water distribution studies within cellulose ethers using differential scanning calorimetry. 1. Effect of polymer molecular weight and drug addition

Abstract

Differential scanning calorimetry (DSC) was employed to characterize the distribution of water in gels produced from a series of hydroxypropylmethylcelluloses (HPMC, Methocel K-series) of different molecular weights (i.e., different viscosity grades). The presence of loosely bound water was characterized as pre-endothermic events occurring at temperatures below the main melting endotherm of free water. Both the magnitude and occurrence of these pre-endothermic events were affected by polymer molecular weight and gel storage time. In addition, the amount of water bound to the polymer depended on polymer molecular weight and gel storage time. The temperature at which frozen water melted within the gels was dependent on polymer concentration, with a depression of extrapolated endothermic melting peak onset occurring with an increase in polymer concentration. The addition of propranolol hydrochloride or diclofenac sodium, as model drugs, affected both the occurrence of pre-endothermic events and the distribution of water within the gels.

New Cyclodextrin Hydrogels Cross-Linked with Diglycidylethers with a High Drug Loading and Controlled Release Ability

“…In these hydrogels, two concomitant effects can occur: (1) an enhancement of the drugYHPMC hydrogen bonds and hydrophobic interactions during the drying; and (2) a sweeping of the drug along by water during the swelling. Additionally, the entrance of water toward the hydrogel core and the diffusion of the drug can be facilitated by the salting out of the HPMC by diclofenac (52). These effects together with the affinity of the drug for the HP"CD determine the release rate.…”

The Properties of HPMC:PEO Extended Release Hydrophilic Matrices and their Response to Ionic Environments

“…Hofmeister effects that might occur at lower concentrations of multivalent ions and drugs [8,[31][32][33][34].…”

Excipient Selection in Oral Solid Dosage Formulations Containing Moisture Sensitive Drugs

“…relative humidity which determines the equilibrium moisture content (McCrystal et al 1999;Agrawal et al 2003a, b).…”

“…Difference in the amount of heat required to increase the temperature of a sample and reference as a function of temperature Energies of water binding in various materials Fielden et al 1988;Yamauchi and Murakami 1991;Joshi and Topp 1992;Khankari et al 1992;McCrystal et al 1997McCrystal et al , 1999Bhaskar et al 1998;Ford 1999;Hatakeyama et al 2000;Agrawal et al 2003b;Heidarian et al 2006 Transition temperatures and enthalpies of sorbed water Identification of energetically distinct states of water,…”

“…Differential scanning calorimetry (DSC), has been successfully used to obtain information about the energies of water binding in various excipients and formulations (Yamauchi and Murakami 1991;Joshi and Topp 1992;Khankari et al 1992;McCrystal et al 1997McCrystal et al , 1999Bhaskar et al 1998;Ford 1999;Hatakeyama et al 2000;Agrawal et al 2003b). DSC testing involves the application of a constant heating or cooling signal to a sample and the subsequent measurement of the total heat flow response (Craig and Johson 1995).…”