Sexually Transmitted DiseasesNCT07500415
Doxi-Rio: Study on the Use of Doxycycline to Prevent Sexually Transmitted Infections in Rio de Janeiro
A study testing Doxycycline in people with Sexually Transmitted Diseases and Syphilis, run by Oswaldo Cruz Foundation at 1 site in Brazil.
Trial 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… Read more about this study
- Who is it for?
- Ages 18 years and olderHealthy volunteers can take part
- Conditions the study is for
- Sexually Transmitted Diseases, Syphilis, Gonorrhea
- What is being tested?
- Doxycycline
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 200 participants
- Where
- 1 siteBrazil
- Study dates
- 28 Oct 2025to May 2028
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- 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
Who cannot join
- 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
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Brazil1 site, 1 recruiting
- Recruiting
Instituto Nacional de Infectologia Evandro Chagas
Rio de Janeiro, Rio de Janeiro, 21040-360
Beatriz Grinsztejn, PhD, +55 2138659128, beatriz.grinsztejn@gmail.com
Beatriz Grinsztejn, PhD
About this study
Official title: Doxi-Rio: Pilot Implementation of Post-exposure Prophylaxis for Sexually Transmitted Infections With Doxycycline in Rio de Janeiro, Brazil
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.
Read more
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.
- Being tested
- Doxycycline
- Medical subject headings
- Sexually Transmitted Diseases, Syphilis, Gonorrhea, Chlamydia Infections, HIV Infections
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
DoxycyclineDrug
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.
| Study group | Role | What they receive |
|---|---|---|
| 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. Receives: Drug: Doxycycline |
What is being measured
The primary outcome is the main question the study is designed to answer.
Incidence of bacterial sexually transmitted infections (STIs)
Cumulative incidence of laboratory-confirmed symptomatic and asymptomatic bacterial STIs (syphilis, gonorrhea, and chlamydia).
Measured: Up to 48 weeks
Secondary outcomes (8)
Incidence of symptomatic and asymptomatic bacterial STIs
Cumulative incidence of laboratory-confirmed symptomatic and asymptomatic bacterial STIs (syphilis, gonorrhea, and chlamydia).
Measured: Up to 48 weeks.
Incidence of specific STIs (chlamydia, gonorrhea, and syphilis)
Cumulative incidence of each STI (chlamydia, gonorrhea, and syphilis), including symptomatic and asymptomatic cases.
Measured: Up to 48 weeks
Antimicrobial resistance in Neisseria gonorrhoeae
Proportion of Neisseria gonorrhoeae isolates with resistance to tetracycline and other relevant antibiotics over time.
Measured: Baseline and up to 48 weeks
Colonization with antimicrobial-resistant bacteria
Proportion of participants colonized with methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum beta-lactamase (ESBL)-producing enterobacteria.
Measured: Baseline and week 48
Adverse events
Occurrence of adverse events (AEs), including serious adverse events (SAEs), grade 3 or 4 AEs, and AEs leading to discontinuation of doxy-PEP.
Measured: From enrollment to 48 weeks
Adherence to doxy-PEP
Adherence measured by self-reported coverage of sexual exposures with doxy-PEP and by doxycycline levels in hair samples.
Measured: Up to 48 weeks
Uptake of doxy-PEP
Proportion of participants who choose to initiate doxy-PEP after counseling.
Measured: At enrollment
Acceptability of doxy-PEP
Participant-reported perceptions, experiences, and acceptability of doxy-PEP assessed through questionnaires and qualitative interviews.
Measured: Up to 48 weeks
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted30 Mar 2026
- Study start28 Oct 2025
- Primary completionOct 2027 (estimated)
- Study completionMay 2028 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Sexually Transmitted DiseasesStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Model description
- 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.
- Masking
- None (open label)
- Enrolment
- 200 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Oswaldo Cruz Foundation
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07500415
- Sponsor's protocol ID
- 87288525.2.0000.5262
- Status last verified
- Mar 2026
- First submitted
- 24 Mar 2026
- Last updated
- 30 Mar 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 30 Mar 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Doxi-Rio: Pilot Implementation of Post-exposure Prophylaxis for Sexually Transmitted Infections With Doxycycline in Rio de Janeiro, Brazil
- ClinicalTrials.gov ID
- NCT07500415
- Acronym / sponsor ID
- 87288525.2.0000.5262
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 200 participants (estimated)
- Lead sponsor
- Oswaldo Cruz FoundationUniversity, hospital or other
- Study start
- 28 Oct 2025 (actual)
- Primary completion
- Oct 2027 (estimated)
- Study completion
- May 2028 (estimated)
- First posted
- 30 Mar 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Study design
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
- Model description
- 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.
| Arm | Type | Receives |
|---|---|---|
| Doxycycline Post-Exposure Prophylaxis (Doxy-PEP) | Experimental | Drug: DoxycyclineParticipants 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. |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (5 listed)
- 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
Key exclusion criteria (2 listed)
- 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
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| DoxycyclineDoxycycline 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. | Drug | Doxycycline Post-Exposure Prophylaxis (Doxy-PEP) |
Primary outcome
Incidence of bacterial sexually transmitted infections (STIs)
Time frame: Up to 48 weeks
Cumulative incidence of laboratory-confirmed symptomatic and asymptomatic bacterial STIs (syphilis, gonorrhea, and chlamydia).
8 secondary outcomes
Incidence of symptomatic and asymptomatic bacterial STIs
Time frame: Up to 48 weeks.
Incidence of specific STIs (chlamydia, gonorrhea, and syphilis)
Time frame: Up to 48 weeks
Antimicrobial resistance in Neisseria gonorrhoeae
Time frame: Baseline and up to 48 weeks
Colonization with antimicrobial-resistant bacteria
Time frame: Baseline and week 48
Adverse events
Time frame: From enrollment to 48 weeks
Adherence to doxy-PEP
Time frame: Up to 48 weeks
Uptake of doxy-PEP
Time frame: At enrollment
Acceptability of doxy-PEP
Time frame: Up to 48 weeks
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 30 Mar 2026.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Doxycycline in people with Sexually Transmitted Diseases and Syphilis, run by Oswaldo Cruz Foundation at 1 site in Brazil.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 5 inclusion and 2 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 30 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Brazil. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Beatriz Grinsztejn, PhD (+55 2138659128, beatriz.grinsztejn@gmail.com), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Incidence of bacterial sexually transmitted infections (STIs) (time frame: Up to 48 weeks). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 30 Mar 2026.