Poly(DL-lactic acid) as a direct compression excipient in controlled release tablets - Part I. Compaction behaviour and release characteristics of poly(DL-lactic acid) matrix tablets

High-molecular weight poly(DL-lactic acid) (PDLA, M-v 85000) was applied as a direct compression excipient in controlled release tablets. PDLA powders with good flowing properties were obtained by milling pre-cooled PDLA granules. Apparent yield pressure values ranged from 44 to 71 MPa for tabletting speeds of 0.033 and 300 mm/s, respectively, pointing to a high ductility and limited strain rate sensitivity. Tablets with good mechanical strength (tensile strength 2.5-3.7 MPa) were prepared at different compaction speeds. Dissolution experiments with different drugs showed that PDLA exhibited good sustained release properties. Initial tablet porosity, lubrication with magnesium stearate and pH of the dissolution medium hardly affected the release rate of the incorporated drug. Drug loads, however, markedly affected the release rate. For drug loads between 20 and 50% w/w, a constant fractional release rate was found. Upon further decreasing of the drug load, the release rate was found to increase. This remarkable finding was explained by the rapid and large increase of the pore volume of the tablets. The results show the unique properties of PDLA and its suitability to be applied as a direct compression and release controlling excipient in matrix tablets for oral drug administration. (C) 1998 Elsevier Science B.V. All rights reserved