Daily Doxycycline to Inform Sexually Transmitted Infection Prophylaxis Regimens

Recent studies have demonstrated the potential utility of single-dose oral doxycycline postexposure prophylaxis (Doxy-PEP) against bacterial sexually transmitted infections (STIs). Additional dosing strategies are being explored that would also provide protection from bacterial STIs. However, the pharmacokinetics of daily doxycycline and specifically the effect of this dosing on effective drug levels in mucosal tissues is underexplored. A previous pilot study conducted by the Division of human immunodeficiency virus (HIV) Prevention (DHP) Laboratory Branch at the Centers for Disease Control and Prevention (CDC) examined the ability of a single 100mg oral dose of doxycycline to penetrate the vaginal and rectal mucosa. However, data regarding daily doxycycline doses and accumulation of doxycycline with multiple doses are lacking.

The purpose of this project is to collect data regarding the ability of daily oral doxycycline taken for 7 days to concentrate in mucosal tissues in people assigned male sex at birth (AMAB) and assigned female sex at birth (AFAB). Results from this study will be compared to results of the previous pilot studies conducted by the DHP Laboratory Branch at CDC.

Healthy people assigned male or female sex at birth will take the first dose of doxycycline during the enrollment visit (Hour -144/Day -6) then will take the next 5 doses at home, one per day for the next 5 days. After 6 consecutive days of dosing, study participants will have samples collected (Hour 0/Day 0) and then will take the final dose. Rectal and vaginal swab samples will be obtained 2 to 4 hours after the final dose of doxycycline. Rectal and vaginal biopsy tissue will be collected 24 hours after the last dose.

Inclusion 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

Exclusion criteria

• 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