Body Compartment Pharmacokinetics of Anti-retroviral Agents That May be Considered for Future On-demand Peri-exposure HIV Prophylaxis Regimens

Inclusion Criteria: 1. HIV-negative man who reports receptive anal sex with another man in the last 6 months 2. Aged 18-49 years 3. Not currently taking PrEP and no plans to initiate during study 4. Not currently taking PEP 5. Able to provide informed consent in English 6. No plans for relocation in the next 3 months 7. Willing to undergo peripheral blood, penile swabs, urine, and rectal biopsy sampling 8. Willing to use study products as directed 9. Willing to abstain from receptive anal intercourse 3 days prior to starting study product and for the duration of the study and for 7 days after any rectal biopsy procedure. 10. Hepatitis B surface antigen (HBsAg) must be negative (screening lab test) 11. Creatine clearance \>60 ml/min Exclusion Criteria: 1. History of inflammatory bowel disease or other inflammatory, infiltrative, infectious or vascular condition involving the lower gastrointestinal tract that, in the judgment of the investigators, may be worsened by study procedures or may significantly distort the anatomy of the distal large bowel 2. Currently infected with hepatitis virus and/ or have liver disease 3. Current or chronic history of kidney disease 4. Significant laboratory abnormalities at baseline visit, including but not limited to: 1. Hgb ≤ 10 g/dL 2. Partial thromboplastin time (PTT) \> 1.5x upper limit of normal (ULN) or international normalized ratio (INR) \> 1.5x ULN 3. Platelet count \<100,000 4. Creatinine clearance \<60 5. HBsAg reactive 5. Any known medical condition that, in the judgment of the investigators, increases the risk of local or systemic complications of endoscopic procedures or pelvic examination, including but not limited to: 1. Uncontrolled or severe cardiac arrhythmia 2. Recent major abdominal, cardiothoracic, or neurological surgery 3. History of uncontrolled bleeding diathesis 4. History of colonic, rectal, or vaginal perforation, fistula, or malignancy 5. History or evidence on clinical examination of ulcerative, suppurative, or proliferative lesions of the anorectal mucosa, or untreated sexually transmitted disease with mucosal involvement 6. Continued need for, or use during the 14 days prior to enrollment, of the following medications: 1. Aspirin or more than 4 doses of NSAIDs 2. Warfarin, heparin (low-molecular weight or unfractionated), platelet aggregation inhibitors, or fibrinolytic agents 3. Any form of rectally administered agent besides lubricants or douching used for sexual intercourse 7. Continued need for, or use during the 90 days prior to enrollment, of the following medications: 1. Systemic immunomodulatory agents 2. Supraphysiologic doses of steroids (short course steroids less than 7 days duration, allowable at the discretion of the investigators) 3. Experimental medications, vaccines, or biologicals 8. Intent to use HIV antiretroviral pre/post-exposure prophylaxis (PrEP or PEP) during the study, outside of the study procedures 9. Symptoms of an untreated rectal sexually transmitted infection (e.g. rectal pain, discharge, bleeding, etc.) 10. Current use of hormonal therapy 11. 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. 12. Participants taking potent inhibitors (e.g. itraconazole, diltiazem) or inducers (e.g. rifampin, phenytoin) of the CYP3A4 enzyme that also metabolizes Genvoya will be excluded from the study