ABSTRACT
Different limitations have been pointed out to microbicide formulations currently used in clinical studies. One of the main issues of tested products seems to be their poor ability to provide an effective, continuous, and durable drug barrier along the epithelial lining that covers the cervicovaginal or rectal mucosae [21,22]. In the particular case of solid dosage forms, this seems to be even more problematic since their ability to disaggregate and/or dissolve in the limited amount of fluid present in the vagina/rectum can jeopardize the efficacy of microbicide compounds. The continuum
of the rectum toward the colon raises even more challenging issues about the spreading of rectally administered products: too little can compromise effectiveness, while too much may lead to safety issues. Nonetheless, higher quantities of a product are expected to be necessary than for vaginal microbicides in order to outdistance and outlast the virus. Another factor to be taken into account is rectal drug absorption, which is generally lower but in line with what happens with oral administration [23,24]. Thus, systemic exposure and even toxicity may be significant when delivering molecules that are well absorbed.
