Pirayavaraporn, Chompak4; Rades, Thomas5; Gordon, Keith C3; Tucker, Ian G4
1 Pharmaceutical Design and Drug Delivery, Department of Pharmacy, Faculty of Health and Medical Sciences, Københavns Universitet2 University of Otago3 Department of Chemistry, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago4 University of Otago5 Pharmaceutical Design and Drug Delivery, Department of Pharmacy, Faculty of Health and Medical Sciences, Københavns Universitet
Coalescence of polymer particles in polymer matrix tablets influences drug release. The literature has emphasized that coalescence occurs above the glass transition temperature (Tg) of the polymer and that water may plasticize (lower Tg) the polymer. However, we have shown previously that nonplasticizing water also influences coalescence of Eudragit RLPO; so there is a need to quantify the different types of water in Eudragit RLPO. The purpose of this study was to distinguish the types of water present in Eudragit RLPO polymer and to investigate the water loss kinetics for these different types of water. Eudragit RLPO was stored in tightly closed chambers at various relative humidities (0, 33, 56, 75, and 94%) until equilibrium was reached. Fourier transform infrared spectroscopy (FTIR)-DRIFTS was used to investigate molecular interactions between water and polymer, and water loss over time. Using a curve fitting procedure, the water region (3100-3,700 cm(-1)) of the spectra was analyzed, and used to identify water present in differing environments in the polymer and to determine the water loss kinetics upon purging the sample with dry compressed air. It was found that four environments can be differentiated (dipole interaction of water with quaternary ammonium groups, water cluster, and water indirectly and directly binding to the carbonyl groups of the polymer) but it was not possible to distinguish whether the different types of water were lost at different rates. It is suggested that water is trapped in the polymer in different forms and this should be considered when investigating coalescence of polymer matrices.
International Journal of Pharmaceutics, 2013, Vol 458, Issue 1, p. 90-98