Microbicide

Microbicide refers to substances designed to reduce the sexual transmission of infections when applied topically inside the vagina or rectum. They are intended to be used before, during, or after sex, depending on the product form, and may act by inactivating pathogens, blocking attachment or entry to mucosal cells, or inhibiting viral replication. Microbicides are studied primarily to prevent HIV, but some products have shown activity against other sexually transmitted infections such as herpes simplex virus.

Forms of microbicide include gels, creams, films, suppositories, and intravaginal or rectal rings. Antiretroviral-based microbicides use drugs such as tenofovir or dapivirine delivered locally to achieve high concentrations at mucosal surfaces with limited systemic exposure.

History has included early candidates that failed to provide protection or caused harm. Nonoxynol-9, for example, increased mucosal irritation and did not reduce HIV risk. Tenofovir gel demonstrated a moderate reduction in HIV acquisition in the CAPRISA 004 trial, with greater effectiveness among users with higher adherence. The dapivirine vaginal ring showed modest protection in large trials, with efficacy influenced by adherence, and has been introduced in several regions under varying regulatory approvals and guidelines. Research has also explored rectal formulations, including tenofovir-based products, with ongoing evaluation of safety and effectiveness.

Usage considerations include adherence, correct timing, and proper dosing, all of which strongly influence effectiveness. Safety concerns focus on mucosal irritation and potential interactions with other products. Microbicides are generally viewed as a complement to, not a replacement for, condoms and regular HIV testing and counseling.

Current status: progress has been made in developing and testing several products, but no universally protective microbicide exists for all populations. Ongoing trials aim to improve efficacy, safety, and user acceptability, with the goal of expanding options for preventing sexually transmitted infections.