This is a double-blinded, randomized, pharmacokinetic and safety study of 3 rectally applied tenofovir microbicide formulations: a vaginal formulation (VF), a reduced glycerin vaginal formulation (RGVF), and a rectal-specific formulation (RF). Nine HIV-negative men will be enrolled.

Each participant will receive two inpatient doses of each radiolabeled study product. The first inpatient dose of each product will be administered without coital dynamics simulation (CDS), while the second inpatient dose will be followed by a CDS procedure at 1-hour post dose with instillation of radiolabeled autologous semen. There will be a washout period of at least 11 days between each dose.

Inclusion Criteria:

1. ≥ Age of 18 at screening
2. Willing and able to communicate in English
3. Willing and able to provide written informed consent to take part in the study
4. Willing and able to provide adequate locator information
5. Understands and agrees to local STI reporting requirements
6. Biologically male
7. HIV-1 uninfected at screening according to the standard DAIDS algorithm 8. Willingness to provide semen sample on multiple occasions

9. Per participant report at screening, a history of consensual RAI at least once within the six months prior to screening 10. Willingness to perform simulated RAI with CDS device 11. Willing to abstain from RAI or any practices which include rectal insertion of any product including those used during sexual intercourse (sex toys) for 48 hours before and after inpatient dosing and willing to refrain from ejaculation for a period of 48 hours prior to each semen collection 12. Must agree to use condoms for the duration of the study 13. Must be in general good health 14. Must agree not to participate in other drug trials 15. Availability to return for all study visits, barring unforeseen circumstances

Exclusion Criteria:

1. Significant colorectal symptom(s) as determined by medical history or by participant self-report (including but not limited to presence of any unresolved injury, infectious or inflammatory condition of the local mucosa, history of inflammatory bowel disease, presence of symptomatic external hemorrhoids, and presence of any painful anorectal conditions that would be tender to manipulation.)

2. At screening: participant-reported symptoms and/or clinical or laboratory diagnosis of active rectal or reproductive tract infection requiring treatment per current CDC guidelines or symptomatic urinary tract infection (UTI). Infections requiring treatment include Chlamydia (CT), gonorrhea (GC), syphilis, active HSV lesions, chancroid, genital sores or ulcers, and, if clinically indicated, genital warts. Note that HSV seropositivity with no active genital lesions is not an exclusion criterion, since treatment is not required. (Note: Allow one re-screening after documented treatment (30 days) in cases where urethral GC/CT identified at screening)

3. At screening:

   • Positive for hepatitis B surface antigen
   • Calculated creatinine clearance less than 60 mL/min by the Cockcroft-Gault formula where creatinine clearance in mL/min = (140 - age in years) x (weight in kg) x (1 for male)/72 x (serum creatinine in mg/dL)
   • Alanine transaminase (ALT) and/or aspartate aminotransferase (AST) > 2.5× the site laboratory ULN

4. Known allergic reaction to methylparaben, propylparaben, sorbic acid, glycerin, glycerol, tenofovir, or other components of the test articles

5. Known HIV-infected partners

6. By participant report at enrollment, history of excessive daily alcohol use (as defined by the CDC as heavy drinking consisting of an average consumption of more than 2 drinks per day for men), frequent binge drinking or illicit drug use that includes any injection drugs, methamphetamines (crystal meth), heroin, or cocaine including crack cocaine, within the past 12 months

7. By participant report, use of any rectally-administered medications, rectally administered products containing N-9 (including condoms), any investigational products, and/or systemic immunomodulatory medications within the 4 weeks prior to the first inpatient visit and throughout study participation

8. History of recurrent urticaria

9. Participants whose whole body (EDE) radiation exposure, per the investigator's records and/or participant report, exceeds 5000mrem/year

10. Any other condition or prior therapy that, in the opinion of the investigator, would preclude informed consent, make study participation unsafe, make the individual 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 substance abuse, or renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, or cerebral disease.