Synthesis and characterization of cross-linked malonylchitosan microspheres for controlled release of acyclovir

The purpose of the present study was to obtain a polymeric system for delayed release of the drug acyclovir (ACV), which can be used for treatment of Herpes simplex and Varicella Zoster. The gelled chitosan (GCT) microspheres were obtained by coacervation-phase separation. They were treated with malonic acid to obtain malonylchitosan (MLCT) microspheres, which were characterized by, Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (13C NMR), elemental analysis (CHN), thermogravimetric analysis (TG/DTG) and scanning electron microscopy (SEM). The drug was encapsulated in MLCT microspheres by a contact adsorption technique, and the final formulation (MLCT-ACV), was analyzed for loading efficiency, degree of swelling and in vitro release profiles. The results obtained support the N-substitution of malonyl groups in the MLCT microspheres. The loading efficiency increased with impregnation time and a major amount of drug was encapsulated after 24 h. The swelling rate was higher in acid pH. The median release time was 5.5 h in pH 1.2 and 6.8. The mechanism involved in release was non-Fickian (0.43 < n < 0.85, n = 0.8474) and Super Case II kinetics (n > 1, n = 1.0491) at pH 1.2 and 6.8, respectively.