CPVA Grafted Poly(sodium 4-styrene sulfonate) and Studies on its Colon Specific for Chronotherapy of Nocturnal Asthma

The paper attempted to develop a colon specific drug delivery system using CPVA grafted poly (sodium 4-styrene sulfonate)(SSS), namely CPVA-g-PSSS microsphere, loaded with theophylline (TP) for chronotherapy of nocturnal asthma. The grafted CPVA-g-PSSS microspheres were prepared by surface-initiated graft-polymerization, and their surface charges were determined by testing Zeta potential. On this basis, the adsorption property of the grafted microspheres CPVA-g-PSSS for theophylline, namely drug loading ability, was mainly investigated, and the adsorption mechanism was explored. The in vitro release behavior of the drug-loaded microspheres was also examined at different pH value and in simulated gastrointestinal fluids. The experiments show the CPVA-g-PSSS microspheres exhibit strong adsorption ability (38.5mg/g) for TP by driving of electrostatic interaction in an acidic medium. The in vitro release behavior of the drug-loaded microspheres is highly pH-sensitive. The in vitro release in simulated gastrointestinal (GI) fluid reveals that drug does not release in the stimulated gastric fluid (pH 1), while in the simulated colonic fluid (pH 7.4), a burst release phenomenon occurs, and 52% TP is released in one hour. An excellent colon-specific drug delivery system is developed to realize a lag time of drug release in 6h runtime of upper gastrointestinal tract, which should be consistent with the demands of chronotherapy of nocturnal asthma.