Nano and microparticulate chitosan-based systems for antiviral topical delivery

Acyclovir (ACV) is one of the drugs of choice for the treatment of epidermal, ocular or systemic herpetic infections. Nevertheless, its trans-mucosal limited absorption and the scarce contact time of the formulation with the mucosal surface - especially in the ocular mucosa - constitute a big limitation of the antiviral efficiency. The most effective way to solve these problems is to increase the quantity and the residence time of the drug over the ocular surface. In order to cope with all these requirements, micro-particles (MPs) and nano-particles (NPs) containing ACV have been developed using cross-linked chitosan with tripolyphosphate (TPP) due to the biocompatibility, bio-adhesion ability and the potential power as penetration enhancer of this polymer. Particles were characterized by Fourier-transformed infrared (FTIR) spectroscopy, X-ray diffraction, SEM, Zeta potential and particle size. Encapsulation efficiency and release profiles in flow through diffusion cells were also determined. Besides the Slug Mucosal Irritation (SMI) assay has been applied as an alternative to the Draize test to predict the mucosal irritation of the selected formulation. FTIR and X-ray results suggested an electrostatic interaction ACV-Chitosan that made ACV be molecularly dispersed within the polymer matrix. Encapsulation efficiency was 75% for MP and 16% for NP. Release profiles in flow through diffusion cells were also determined. From the diffusion profiles, it was found that the amounts of ACV effectively diffused in 24h were 30, 430 and 80 μg for the ACV solution, MP and NP respectively. SMI results showed that chitosan-based particles induced moderate irritation and mild tissue damage, what supposes that ACV-MP constitute a promising alternative for further development of an antiviral formulation.