Yosanon Pattanasriroj. Influence of drug-polymer interaction on physicochemical properties and drug release characteristics of matrix tablets . Master's Degree(Pharmaceutics). Mahidol University. : Mahidol University, 2003.
Influence of drug-polymer interaction on physicochemical properties and drug release characteristics of matrix tablets
Abstract:
The objective of the present study was to investigate the influence of drug-polymer interaction on physicochemical properties and drug release characteristics of matrix tablets. Drug-polymer mixtures were prepared by physical mixing and solid dispersion methods at various ratios of drug to polymer. Acyclovir-ethylcellulose 20 cps, diltiazem hydrochloride-ethylcellulose 10 cps, and theophylline Eudragit® L 100 mixtures were characterized for the drug-polymer interaction by the use of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), differential scanning calorimetry (DSC), powder X-ray diffraction analysis (PXRD), and nuclear magnetic resonance spectroscopy (NMR). The drug release studies from matrix tablets of drug-polymer mixtures were conducted in 0.1 N HCl for 24 hrs. The results obtained indicated that the interaction between drug and polymer could significantly affect the physical properties and drug release kinetics. The crystalinity of the drug-polymer mixtures prepared by solid dispersion method was found to decrease with increasing polymer concentration. The probable mechanisms of interaction found between acyclovir and ethylcellulose were proposed as follows: (1) the hydroxyl groups in ethylcellulose macromolecule may interact with the imine group of acyclovir molecule by the bridge CH=N····HO, (2) the ether oxygen in the cellulose ring may interact with hydroxyl group of acyclovir by the bridge -OH····O. These interactions cause a reduction in drug release from polymeric matrix tablets because of the partial drug adsorption onto the polymer chain. The probable mechanism of interaction found between diltiazem hydrochloride and ethylcellulose would be between the ether oxygen in the cellulose ring and the methyl group of the dimethylaminoethyl side chain of diltiazem molecule by the bridge CH .O. This interaction may be the cause of minute amount of diltiazem hydrochloride being bound to ethylcellulose, in form of molecular dispersion, without being released from the matrix tablets. Moreover, theophylline-Eudragit® L 100 mixtures were found to exhibit the dipole-dipole interaction between the N1 of theophylline and CO-O- group of Eudragit® L 100, which may converselyenhance the release of theophylline from the matrix tablets.