Doxi-Rio: Study on the Use of Doxycycline to Prevent Sexually Transmitted Infections in Rio de Janeiro

NCT07500415 | Recruiting

• 1 other identifier: 87288525.2.0000.5262
• Study Type: interventional
• Target: 200
• Locations: 1 country
• Sites: 1

Brief Summary

The goal of this clinical trial is to learn if doxycycline post-exposure prophylaxis (doxy-PEP) can help prevent bacterial sexually transmitted infections (STIs) among sexual and gender minorities in Rio de Janeiro, Brazil, including men who have sex with men, transgender women, and travestis who are living with HIV or using HIV pre-exposure prophylaxis (PrEP). Bacterial STIs such as syphilis, gonorrhea, and chlamydia remain common in these populations, even with existing prevention strategies. This study aims to answer the following questions: whether doxy-PEP can reduce the number of new STIs, whether it is safe and well tolerated, whether participants use it as recommended, and whether its use may contribute to antibiotic resistance or changes in the body's natural bacteria. Doxy-PEP involves taking a dose of doxycycline, an antibiotic, shortly after sexual activity to reduce the risk of acquiring STIs. Participants will first receive information and counseling about doxy-PEP, including its possible benefits and risks, and will then choose whether or not to use this prevention strategy. Those who choose to use doxy-PEP will take doxycycline after sex as instructed and will be followed for up to 48 weeks, with clinic visits approximately every three months. During these visits, participants will be tested for STIs, monitored for side effects, and asked about medication use, sexual health, and overall well-being. Researchers will collect information on new STI diagnoses, safety, and how consistently participants use doxy-PEP. The study will also explore participants' experiences and perceptions of this strategy. The results of this study will help determine whether doxy-PEP is a practical and acceptable approach for STI prevention in Brazil and may inform future public health strategies.

Conditions

Sexually Transmitted Diseases; Syphilis; Gonorrhea; Chlamydia Infections; HIV Infections

Outcome Measures

Primary Outcomes (1)

• Incidence of bacterial sexually transmitted infections (STIs)

  Cumulative incidence of laboratory-confirmed symptomatic and asymptomatic bacterial STIs (syphilis, gonorrhea, and chlamydia).

  Up to 48 weeks

Secondary Outcomes (8)

• Incidence of symptomatic and asymptomatic bacterial STIs

  Up to 48 weeks.

• Incidence of specific STIs (chlamydia, gonorrhea, and syphilis)

  Up to 48 weeks

• Antimicrobial resistance in Neisseria gonorrhoeae

  Baseline and up to 48 weeks

• Colonization with antimicrobial-resistant bacteria

  Baseline and week 48

• Adverse events

  From enrollment to 48 weeks

Study Arms (1)

Doxycycline Post-Exposure Prophylaxis (Doxy-PEP)

EXPERIMENTAL

Participants who choose to initiate doxycycline post-exposure prophylaxis (doxy-PEP) after receiving counseling on its risks and benefits. Participants will take doxycycline after sexual activity as instructed and will be followed for up to 48 weeks with regular clinical visits, including testing for sexually transmitted infections, safety assessments, and adherence evaluation. Participants who initially decline doxy-PEP may choose to initiate it at any time during the study.

Drug: Doxycycline

Interventions

Doxycycline DRUG

Doxycycline 200 mg taken orally within 72 hours after sexual activity, not exceeding one dose per 24 hours and a maximum of three doses per week.

Doxycycline Post-Exposure Prophylaxis (Doxy-PEP)

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• Individuals assigned male at birth (cisgender or transgender men), transgender women, or travestis who have sex with men
• Age ≥18 years
• Living with HIV or currently using HIV pre-exposure prophylaxis (PrEP) for at least 6 months
• History of at least one bacterial sexually transmitted infection (chlamydia, gonorrhea, or syphilis) in the past 12 months (laboratory-confirmed or self-reported)
• Willing and able to provide informed consent

You may not qualify if:

• Known allergy or hypersensitivity to doxycycline or other tetracycline-class antibiotics
• Current use of medications that may significantly interact with doxycycline or are contraindicated, including systemic retinoids, barbiturates, carbamazepine, or phenytoin

Sponsors & Collaborators

• Oswaldo Cruz Foundation: lead

Study Sites (1)

Instituto Nacional de Infectologia Evandro Chagas

Rio de Janeiro, Rio de Janeiro, 21040-360, Brazil

RECRUITING

MeSH Terms

Conditions

Sexually Transmitted Diseases; Syphilis; Gonorrhea; Chlamydia Infections; HIV Infections

Interventions

Doxycycline

Condition Hierarchy (Ancestors)

Communicable Diseases; Infections; Genital Diseases; Urogenital Diseases; Disease Attributes; Pathologic Processes; Pathological Conditions, Signs and Symptoms; Treponemal Infections; Spirochaetales Infections; Gram-Negative Bacterial Infections; Bacterial Infections; Bacterial Infections and Mycoses; Sexually Transmitted Diseases, Bacterial; Neisseriaceae Infections; Chlamydiaceae Infections; Blood-Borne Infections; Sexually Transmitted Diseases, Viral; Lentivirus Infections; Retroviridae Infections; RNA Virus Infections; Virus Diseases; Immunologic Deficiency Syndromes; Immune System Diseases

Intervention Hierarchy (Ancestors)

Tetracyclines; Naphthacenes; Polycyclic Aromatic Hydrocarbons; Hydrocarbons, Aromatic; Hydrocarbons, Cyclic; Hydrocarbons; Organic Chemicals; Polycyclic Compounds

Central Study Contacts

Beatriz Grinsztejn, PhD

CONTACT

+55 2138659128; beatriz.grinsztejn@gmail.com

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NA
• Masking: NONE
• Purpose: TREATMENT
• Intervention Model: SINGLE GROUP
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Model Details: This is an open-label, single-group, pilot implementation study evaluating doxycycline post-exposure prophylaxis (doxy-PEP) for the prevention of bacterial sexually transmitted infections. All eligible participants receive counseling and are offered the option to initiate doxy-PEP. Participants who choose to initiate doxy-PEP are followed prospectively for up to 48 weeks, with regular clinical and laboratory assessments, including testing for sexually transmitted infections, safety monitoring, and adherence evaluation. Participants who initially decline doxy-PEP may opt to initiate it at any time during the study. The study aims to assess feasibility, acceptability, safety, adherence, and impact on STI incidence and antimicrobial resistance in a real-world setting.

Study Record Dates

• First Submitted: March 24, 2026
• First Posted: March 30, 2026
• Study Start: October 28, 2025
• Primary Completion (Estimated): October 1, 2027
• Study Completion (Estimated): May 1, 2028
• Last Updated: March 30, 2026

Record last verified: 2026-03

Data Sharing

• IPD Sharing: Will not share

Locations

BR (1)