Doxy-Post-exposure Prophylaxis (DOXY-PEP)

Inclusion Criteria: Aged 18-59 years Assigned male sex or female sex at birth In good general health Not currently taking doxycycline or other tetracycline-derived antibiotics and no plans to initiate during the study For HIV-positive people, on stable antiretroviral therapy with an undetectable viral load and CD4 count> 300ul/ml Willing to use condoms consistently for the duration of the study Able to provide informed consent No plans for relocation in the next 4 months Not pregnant and does not plan on getting pregnant for the duration of the study Willing to undergo peripheral blood, urine, rectal or vaginal secretion collection, and a rectal or vaginal and cervical biopsy procedure Willing to use study products as directed Creatinine clearance >60 ml/min Exclusion Criteria: Currently infected with hepatitis virus and/ or has liver disease Current or chronic history of kidney disease or CrCl<60 ml/min Continued need for, or use during the 90 days prior to enrollment, of the following medications: Systemic immunomodulatory agents Supraphysiologic doses of steroids (short course steroids less than 7 days duration, allowable at the discretion of the investigators) Chemotherapy or radiation for treatment of malignancy Experimental medications, vaccines, or biologicals Intent to use doxycycline or other tetracycline-derived antibiotics during the course of the study, outside of the study procedures 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 Known allergic reaction to study drugs. Significant laboratory abnormalities at baseline visit for rectal biopsies, including but not limited to: Hgb ≤ 10 g/dL PTT > 1.5x ULN or INR > 1.5x ULN Platelet count <100,000