Determination of moisture content in relation to thermal behaviour and plasticization of Eudragit RLPO.
ABSTRACT Coalescence of polymer particles on thermal treatment plays an important role in effective control of drug release from these matrix systems. The water content of the polymer may influence coalescence since it is well established that sorbed water may act as a plasticizer, or cause other changes in mechanical properties. However, these effects depend on the amount and type (plasticizing/nonplasticizing) of water present. The purpose of this study was to determine the accuracy of different methods used to determine moisture content of a polymer (Eudragit RLPO) and to determine the types water present. The polymer powder was stored at various relative humidities (33, 56, 75, 94%). Four water determination methods, [weight loss on drying, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Karl Fischer titration (KFT)] were utilized to determine moisture content. DSC was used to study the thermal behaviour of moist and dry samples. The Gordon-Taylor equation was used to calculate the amount of plasticizing water. Scanning electron microscopy was employed to examine the morphology of the polymer particles after thermal analyses. It is concluded that KFT accurately determines the total water content but that the thermal methods underestimate total water content. However KFT does not indicate the type of water present. The Gordon-Taylor model suggests that only about 25% of the water in the polymer containing 10% water was acting as a plasticizer. Complementary methods should be used to measure the water content of pharmaceutical polymers.
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ABSTRACT: 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 (3100-3700cm(-1)) of the spectra was analysed, 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 10/2013; · 3.99 Impact Factor
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ABSTRACT: Abstract A multiple-unit floating alginate bead drug delivery system with prolonged stomach retention time was developed in this study. The floating alginate beads were prepared by ionic cross-linking method, using CaCO3 as the gas-forming agent. Over 92% of the beads remained floating after 9 h. In order to prepare sustained-release dosage forms of dipyridamole, the solid dispersion technique was applied using a blend of Eudragit L100 and Eudragit RLPO. Afterwards, the solid dispersions of dipyridamole were incorporated into the floating alginate beads. The drug release was modified by changing the ratio of Eudragit RLPO and Eudragit L100 in the solid dispersions. The in vivo results showed that the relative bioavailability of alginate beads was enhanced by approximately 2.52-fold compared with that of the commercial tablet. Therefore, our study illustrated the potential use of floating alginate beads combined with the solid dispersion technique for the delivery of acid-soluble compounds, such as dipyridamole.Drug Development and Industrial Pharmacy 03/2014; · 1.54 Impact Factor