• Macroscopic evidence of damage to the cervical, vulvar, or vaginal epithelium, including ulceration and other lesions, severe erythema, or severe edema, related or not related to the study gel or applicator
  

• Adherence to the study gel regimen
  
• acceptability of the study gel
  

While the male condom is effective in preventing sexual transmission of HIV, its use is hampered by deeply rooted cultural and social barriers. About half of all HIV infections worldwide occur in women, yet the only available female-controlled method of HIV prevention is the female condom. Alternative prevention tools, such as vaginal microbicides, are urgently needed to slow the rapid spread of heterosexual HIV infection.

This study will last 24 weeks, with an additional 10 weeks of follow-up for participants with chronic hepatitis B virus (HBV) infection. Participants will be randomly assigned to one of four arms. Arm A participants will insert a vaginal tenofovir 1% gel two hours prior to vaginal intercourse for a maximum of two daily applications. Arm B participants will insert a vaginal placebo gel two hours prior to vaginal intercourse for a maximum of two daily applications. Arm C participants will insert a vaginal tenofovir 1% gel once daily at bedtime or during the longest period of daily rest. Arm D participants will insert a vaginal placebo gel once daily at bedtime or during the longest period of daily rest.

A medical and menstrual history update, pregnancy test, HIV and sexually transmitted infections (STI) risk reduction counseling, and interview to assess behaviors toward vaginal gel use will occur during all study visits. HIV/STI counseling and testing, urinalysis, and blood collection will occur at study entry and at Week 24. Pelvic exam with colposcopy and vaginal swab collection will occur at study entry and Weeks 4, 12, and 24. For participants with chronic HBV, additional blood will be collected to monitor hepatitis B infection at study entry and Weeks 12, 24, 28, 32, and 36.