Daily Doxycycline to Inform Sexually Transmitted Infection Prophylaxis Regimens

Daily Doxy: Study of Persons Receiving Daily Doxycycline to Inform Sexually Transmitted Infection Prophylaxis Regimens

The goal of this project is to collect data regarding the concentrations of doxycycline in mucosal tissues after daily dosing for 7 days in people assigned male sex at birth (AMAB) and assigned female sex at birth (AFAB) to inform future studies of doxycycline to protect against bacterial sexually transmitted infections (STIs).

Study Overview

• Status: Completed
• Conditions: Sexually Transmitted Infection
• Intervention / Treatment: Drug: Doxycycline

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Actual): 24
• Phase: Phase 4

Contacts and Locations

Study Locations

• United States
  • Georgia
    • Atlanta, Georgia, United States, 30322
      • Hope Clinic

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Doxycycline; Study participants taking 7 consecutive, daily doses of 100mg of Doxycycline.	Drug: Doxycycline; Doxycycline (DOX) will be given orally at 100mg doses. Participants will take the study medication for 7 consecutive days.; Other Names: Monodox; Oracea; Doxy-100

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Doxycycline Concentration in Rectal Tissue	Rectal tissue doxycycline concentrations collected 24 hours after 7 daily (T7) doses of 100 mg of doxycycline were determined in assigned male sex at birth (AMAB) participants.	24 hours after last dose (Hour 24/Day 1)
Doxycycline Concentration in Vaginal Tissue	Vaginal tissue doxycycline concentrations collected 24 hours after 7 daily (T7) doses of 100 mg of doxycycline were determined in Assigned female sex at birth (AFAB) participants.	24 hours after last dose (Hour 24/Day 1)

Collaborators and Investigators

• Sponsor: Emory University
• Collaborators: Centers for Disease Control and Prevention
• Investigators: Principal Investigator: Colleen Kelley, MD, MPH, Emory University

Publications and helpful links

General Publications

• Daly MB, Spandau M, Edwards TE, Dinh C, Fountain J, Dienhart JA, Conway-Washington C, Kelley C, Heneine W, Haaland R. Chelating anticoagulants reduce plasma doxycycline measurements: implications for doxy PEP monitoring. Expert Rev Clin Pharmacol. 2026 Jan-Feb;19(2):199-205. doi: 10.1080/17512433.2026.2632931. Epub 2026 Feb 19.

Study record dates

Study Major Dates

• Study Start (Actual): September 13, 2024
• Primary Completion (Actual): April 29, 2025
• Study Completion (Actual): April 29, 2025

Study Registration Dates

• First Submitted: August 6, 2024
• First Submitted That Met QC Criteria: August 6, 2024
• First Posted (Actual): August 9, 2024

Study Record Updates

• Last Update Posted (Actual): May 1, 2026
• Last Update Submitted That Met QC Criteria: April 13, 2026
• Last Verified: June 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Urogenital Diseases; Genital Diseases; Pathologic Processes; Disease Attributes; Infections; Communicable Diseases; Pathological Conditions, Signs and Symptoms; Sexually Transmitted Diseases; Organic Chemicals; Hydrocarbons; Hydrocarbons, Cyclic; Polycyclic Aromatic Hydrocarbons; Hydrocarbons, Aromatic; Polycyclic Compounds; Naphthacenes; Tetracyclines; Doxycycline
• Other Study ID Numbers: STUDY00007429; CDC-STUDY00007429 (Other Identifier: Centers for Disease Control and Prevention)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data underlie the results published for this study (including text, tables, figures, and appendices) will be made available for sharing with other researchers.
• IPD Sharing Time Frame: Individual participant data will be made available for sharing after publication of the primary manuscript from this study.
• IPD Sharing Access Criteria: Interested investigators can request de-identified data by email for secondary data analyses and/or meta-analyses.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No