Daily Doxycycline to Inform Sexually Transmitted Infection Prophylaxis Regimens

Eligibility Criteria

• * 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 cluster of differentiation 4 (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
• * Current or chronic history of liver disease
• * 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:
• * Hemoglobin (Hgb) ≤ 10 g/dL
• * Partial thromboplastin time (PTT) \> 1.5x upper limit of normal (ULN) or international normalised ratio (INR) \> 1.5x ULN
• * Platelet count \<100,000