Development of an oral sustained release drug delivery system utilizing pH-dependent swelling of carboxyvinyl polymer.

A new oral sustained-release (SR) drug delivery system utilizing pH-dependent swelling of carboxyvinyl polymer (CP) has been proposed. This swelling polymer incorporation layer system, referred to as SPILA system, consists of core granules coated with a mixture of CP, water insoluble polymer, and water-soluble polymer (WP). Release profiles of metoprolol tartrate (ME) from SPILA system were pH dependent: drug release was slower in the medium of pH 1.2 than in the medium of pH 6.8 due to a coating layer with pH-dependent swelling polymer, CP. Lower C(max), longer T(max), longer MRT and higher AUC values were obtained following administration of SR granules based on SPILA system to beagle dogs compared with pH-independent SR granules having a coating layer without CP, while both SR granules provided similar in vitro release profiles. Moreover, using morphine hydrochloride (MO), in vitro and in vivo performances of the SPILA system were investigated. pH-dependency on the release profiles of MO from SPILA system was more evident when the amount of CP incorporated in SPILA system was increased. AUC and MRT values following administration of SR granules of MO with a coating layer containing 8% of CP to beagle dogs were 191 ng h/mL and 10.6 h respectively, while those following SR granules of MO with a coating layer containing 1% of CP to beagle dogs were 86.4 ng h/mL and 5.86 h, respectively. An important role of CP in the release-regulating layer of SPILA system for keeping the higher and more extended plasma levels of morphine free base was confirmed from the in vivo performance of SPILA system.