Evaluation of polymer combinations in vaginal mucoadhesive tablets for the extended release of acyclovir

Genital herpes, caused by herpes simplex virus type 2 (HSV-2), affects nearly 500 million people, mostly women. Since the main route of transmission is sexual contact, the development of an acyclovir extended-release vaginal microbicide would be a suitable tool for the prevention of virus transmission. In this work, we evaluated the potential of three polymers with different characteristics (chitosan, xanthan gum and ethyl cellulose) for obtaining acyclovir extended-release vaginal tablets. By combining the polymers, certain useful synergies were observed to modify their mucoadhesive capacity and control drug release. In the swelling studies, it observed that a polyelectrolyte complex with more moderate swelling and sustained gelation was formed between chitosan and xanthan gum exclusively in acidic medium (simulated vaginal fluid). This complex allowed prolonging the mucoadhesion of the tablets in ex vivo studies performed with vaginal mucosa, which would translate into better retention in the vagina after administration. In addition, the combination of chitosan and xanthan gum allowed obtaining a controlled release of acyclovir for 5 days, regardless of the pH of the medium, which would guarantee that drug release continues even in the presence of seminal fluid.