Optimization of Tenofovir release from mucoadhesive vaginal tablets

The use of sustained-release mucoadhesive vaginal tablets of antiretroviral drugs as microbicidal formulations can be an effective strategy for reducing the sexual transmission of HIV from men to women, which is a main problem particularly in low- and middle-income countries. Different polymers (hydroxypropylmethyl cellulose (HPMC), chitosan, guar gum and Eudragit® RS) have proven some good features for this purpose. At this work, these polymers have been combined in pairs in different proportions to enhance the advantages offered by each one individually. The in vitro release of tenofovir from the matrices, ex vivo mucoadhesive capacity (evaluated on vaginal mucosa) and the degree of swelling in simulated vaginal fluid have been assessed. A multimodal pore size distribution is observed in porosimetry studies ‐carried out with swelling witnesses-, due to the contribution of polymers with different swelling behaviour to the pore formation, and it is corroborated by scanning electron microscopy. X-ray diffraction technique confirms the changes in crystallinity of the formulation after swelling. We can report that the combination of HPMC and chitosan in the same formulation may be useful for the prevention of sexual transmission of HIV, since tablets can be obtained that remain adhered to the vaginal mucosa for 96 hours, so the drug is released in a sustained manner for 72 hours. When the formulation contains more chitosan than HPMC the swelling is moderate, making it more comfortable for women to apply.