Safety and Acceptability Study of the UC-781 Microbicide Gel Applied Rectally

Inclusion Criteria: Men who meet the following 10 criteria and women who meet the following 12 criteria are eligible for inclusion in the study: 1. ≥ Age of 18 2. HIV-1 status antibody negative as documented at screening 3. Understands and agrees to local STI reporting requirements 4. Able and willing to communicate in English 5. Able and willing to provide written informed consent 6. Able and willing to provide adequate information for locator purposes 7. Availability to return for all study visits 8. A history of consensual RAI at least once in lifetime: * Required to assure that subjects have a context for the acceptability assessments 9. Willing to abstain from insertion of anything per rectum other than the study gel for the 1 week prior to treatment, 1 week prior each flexible sigmoidoscopy (i.e., during week of study gel use), and 1 week after each flexible sigmoidoscopy 10. Must agree to use condoms for the duration of the study In addition to the criteria listed above, female participants must meet the following criteria: 11. Negative pregnancy test 12. Post-menopausal or using an acceptable form of contraception (e.g. barrier method, IUD, hormonal contraception, surgical sterilization, or vasectomization of male partner). If the female subject has female partners only, the method of contraception will be noted as a barrier method in the study documentation. Exclusion Criteria: Individuals who meet any of the following criteria at screening will be excluded from the study: 1. HIV positive at baseline 2. History of inflammatory bowel disease 3. Active inflammatory condition of the GI tract at baseline 4. Active rectal infection at baseline 5. ≥ Grade 2 laboratory abnormality (≥ Grade 1 potassium, magnesium, chloride, sodium, and calcium) at baseline 6. History of an underlying cardiac arrhythmia or renal disease that may be exacerbated by electrolyte abnormalities 7. History of severe or recent cardiac or pulmonary event 8. History of a large aortic aneurysm 9. History of significant gastrointestinal bleeding 10. Allergy to methylparaben, propylparaben, sorbic acid 11. History of alcoholism or IV drug abuse 12. Unwillingness to refrain from chronic use of aspirin and NSAIDs 13. Use of warfarin or heparin 14. Use of systemic immunomodulatory medications within 4 weeks of Visit 2 15. Use of rectally administered medications, with the exception of over-the-counter enemas, within 4 weeks of Visit 2 16. Use of product containing nonoxyl-9 rectally within 4 weeks of Visit 2 17. Use of any investigational products within 4 weeks of Visit 2 18. Any other clinical condition or prior therapy that, in the opinion of the investigator, would make the patient unsuitable for the study or unable to comply with the study requirements. Such conditions may include, but are not limited to, current or recent history of severe, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, or cerebral disease. In addition to the criteria listed above, female participants will be excluded if the meet any of the following criteria: 19. Pregnancy 20. Breastfeeding 21. Female of child-bearing potential unwilling to use acceptable form of contraception