Doxycycline for Sexually Transmitted Infections

Recruiting at 6 trial locations

Overseen By Ramin Azmin

Age: 18+

Sex: Male

Trial Phase: Academic

Sponsor: Jonathan Troy Grennan

Must not be taking: Barbiturates, Phenytoin, Carbamazepine, Isotretinoin

Disqualifiers: Allergy to doxycycline, Pregnancy, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Approved in 4 Jurisdictions This treatment is already approved in other countries

Compensation: Varies

Number of Visits: Unknown

Duration: 12 months

560 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial explores new methods to prevent sexually transmitted infections (STIs) such as syphilis, chlamydia, and gonorrhea using the antibiotic doxycycline. Researchers compare two approaches: taking doxycycline daily (PrEP) or after high-risk sexual activity (PEP). They aim to determine which method more effectively prevents STIs among men who have sex with men, particularly those with a recent STI. Ideal participants are men who have had multiple male partners and a past STI within the last year. As an unphased trial, this study offers participants the chance to contribute to groundbreaking research that could lead to new STI prevention strategies.

Will I have to stop taking my current medications?

The trial requires that you stop using certain medications that could lower doxycycline levels, such as barbiturates, phenytoin, and carbamazepine. If you are using isotretinoin, you will also need to stop taking it to participate.

Is there any evidence suggesting that this trial's treatments are likely to be safe?

Research has shown that doxycycline is generally safe to use. A review found that taking doxycycline for extended periods, such as more than eight weeks, is usually well-tolerated, with most people not experiencing serious side effects.

Doxycycline has proven effective in preventing sexually transmitted infections (STIs). The CDC states that taking 200 mg of doxycycline within 72 hours after sex can reduce the risk of syphilis and chlamydia infections by over 70%.

Overall, doxycycline is considered safe for many people, though some might experience minor side effects like nausea or an upset stomach. Consulting a doctor about any concerns before starting doxycycline is important. ^{1 2 3 4 5}

Why are researchers excited about this trial's treatments?

Researchers are excited about these treatments because they offer a new approach to preventing sexually transmitted infections (STIs). Unlike traditional treatments that focus on curing infections after they occur, doxycycline is being studied for its potential as a preventive measure. The STI PrEP arm involves taking doxycycline daily to prevent STIs before they happen, while the STI PEP arm uses doxycycline after risky sexual encounters to prevent infection. This proactive strategy could significantly reduce the incidence of STIs, providing a valuable tool in sexual health management.

What evidence suggests that doxycycline might be an effective treatment for bacterial STIs?

This trial will evaluate doxycycline for preventing sexually transmitted infections (STIs) using two approaches. In the STI PrEP arm, participants will take 100mg doxycycline capsules orally each day for 12 months. Studies have shown that doxycycline can reduce STIs when used as a preventive measure before exposure (PrEP). In the STI PEP arm, participants will take 200mg doxycycline orally within 24-72 hours after each sexual encounter deemed at risk. Research shows that using doxycycline after exposure (PEP) decreases the chance of contracting bacterial STIs like gonorrhea, chlamydia, and syphilis. In some studies, doxycycline use led to a 56% reduction in overall STI rates. These findings suggest that doxycycline could be a useful tool in preventing bacterial STIs. ^{1 6 7 8 9}

Who Is on the Research Team?

Troy Grennan, MD

Principal Investigator

University of British Columbia

Are You a Good Fit for This Trial?

The DISCO trial is for gay, bisexual, and other men who have sex with men (gbMSM) over 18 years old. Participants must have had multiple male partners and at least one bacterial STI in the past year. They should not be on certain drugs that affect doxycycline levels, allergic to tetracyclines, using doxycycline regularly or taking isotretinoin.

Inclusion Criteria

I plan to be sexually active with multiple male partners this year.

I had syphilis, gonorrhea, or chlamydia treated in the last year.

I have had sexual activity with more than one male partner in the last year.

Exclusion Criteria

You are allergic to doxycycline or tetracyclines.

I am capable of becoming pregnant.

I am currently taking isotretinoin.

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Treatment

Participants receive doxycycline-based STI PrEP or PEP for the prevention of bacterial STIs

12 months

Regular visits for monitoring and assessment

Follow-up

Participants are monitored for safety, effectiveness, and antimicrobial resistance after treatment

60 weeks

Open-label extension (optional)

Participants may opt into continuation of treatment long-term

Long-term

What Are the Treatments Tested in This Trial?

Interventions

• Doxycycline Hyclate

Trial Overview This study tests whether Doxycycline Hyclate can prevent bacterial STIs like syphilis, chlamydia, and gonorrhea in gbMSM. It's a randomized controlled trial comparing two prevention strategies: pre-exposure prophylaxis (PrEP) versus post-exposure prophylaxis (PEP).

How Is the Trial Designed?

Group I: STI PrEP arm Experimental Treatment 1 Intervention

doxycycline capsules 100mg orally daily for 12 months. Though the usual treatment dose of doxycycline is 100mg twice daily

Group II: STI PEP arm Experimental Treatment 1 Intervention

doxycycline 200mg orally once within 24-72 hours following each sexual encounter deemed at risk (i.e. condomless anal or oral sex), to a maximum of six pills (i.e. 600 mg total) per week

Doxycycline Hyclate is already approved in United States, European Union, Canada for the following indications:

Approved in United States as Doxycycline Hyclate for:

• Acne
• Malaria
• Skin infections
• Sexually transmitted infections
• Lyme disease

Approved in European Union as Doxycycline Hyclate for:

• Acne
• Malaria
• Skin infections
• Sexually transmitted infections
• Lyme disease

Approved in Canada as Doxycycline Hyclate for:

• Acne
• Malaria
• Skin infections
• Sexually transmitted infections
• Lyme disease

Who Is Running the Clinical Trial?

Jonathan Troy Grennan

Lead Sponsor

Trials

1

Recruited

560+

Canadian Institutes of Health Research (CIHR)

Collaborator

Trials

1,417

Recruited

26,550,000+

Published Research Related to This Trial

Doxycycline is a well-established, broad-spectrum antibiotic that is effective against various bacterial infections, including sexually transmitted infections (STIs), and is particularly beneficial due to its high tissue diffusion and long half-life, allowing for convenient oral dosing.

With the rise of antibiotic resistance in first-line STI treatments, doxycycline is being reconsidered as a safe and effective option for managing STIs, especially in populations at higher risk, such as men who have sex with men (MSM) and those living with HIV.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Doxycycline in the management of sexually transmitted infections. Peyriere, H., Makinson, A., Marchandin, H., et al.[2019]

Doxycycline (Doxy-PEP) has been shown to effectively prevent bacterial sexually transmissible infections (STIs) like chlamydia, gonorrhoea, and syphilis in men who have sex with men with a history of multiple STIs.

Concerns remain regarding potential adverse effects of Doxy-PEP, including the risk of developing antimicrobial resistance and disrupting the microbiome, which clinicians need to discuss with patients considering this preventive treatment.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Interim position statement on doxycycline post-exposure prophylaxis (Doxy-PEP) for the prevention of bacterial sexually transmissible infections in Australia and Aotearoa New Zealand - the Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM). Cornelisse, VJ., Ong, JJ., Ryder, N., et al.[2023]

A systematic review of 7 studies involving oral tetracycline-class antibiotics, including doxycycline, indicated that these antibiotics can increase resistance to tetracyclines in normal flora, particularly in subgingival, gastrointestinal, and upper respiratory tract bacteria.

While some studies showed a transient increase in non-tetracycline resistance, the overall impact on non-tetracycline AMR was minimal, suggesting that the use of doxycycline for STI prophylaxis may require careful monitoring of antimicrobial resistance in commensal bacteria.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A systematic review of the impacts of oral tetracycline class antibiotics on antimicrobial resistance in normal human flora. Truong, R., Tang, V., Grennan, T., et al.[2022]

Doxycycline hyclate (DH) has a favorable safety profile, especially in its delayed-release form (Doryx), compared to the standard powder form (Vibramycin), making it a safer option for treating conditions like acne and rosacea.

Despite historical safety concerns associated with tetracyclines, including gastrointestinal issues and effects on tooth development, subantimicrobial dosing of DH has shown to be effective and safe for acne treatment, supporting its continued use in dermatology.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

The use and safety of doxycycline hyclate and other second-generation tetracyclines. Sloan, B., Scheinfeld, N.[2022]

Doxycycline, a commonly used antibiotic, was linked to a case of acute pancreatitis in a female patient who had been taking it for acne treatment, highlighting a rare but serious side effect.

The adverse reaction was confirmed as 'definite' using the WHO causality assessment and the Naranjo scale, emphasizing the importance of monitoring for potential side effects even with generally safe medications.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Doxycycline-Induced Acute Pancreatitis: A Rare Adverse Event. Rawla, P., Raj, JP.[2020]

Doxycycline (200 mg/day for 2 weeks) effectively eradicated Chlamydia trachomatis in 89% of patients by the 3rd day and maintained a 100% eradication rate by the 14th day, demonstrating its efficacy in treating nongonococcal urethritis.

The treatment was well-tolerated with no reported side effects, and a significant reduction in symptoms was observed, with 83% of patients symptom-free by the 7th day and 100% by the 14th day.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

[Clinical studies on doxycycline in the treatment of nongonococcal urethritis by Chlamydia trachomatis]. Ito, Y., Katoh, N., Takeda, A., et al.[2020]

Doxycycline is an effective antibiotic for treating various infections, particularly respiratory tract diseases like pneumonia, as demonstrated in a study involving 49 patients.

The drug shows good safety and compatibility, especially in children, and achieves effective serum levels when administered at a dose of 4 mg/kg in two injections.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

[Clinical and pharmacokinetic researches of doxycyclin vibravenös in childhood (author's transl)]. Weingärtner, L., Straube, D., Baum, W., et al.[2013]

Doxycycline has been shown to lower the risk of sexually transmitted diseases (STDs), making it a potentially effective preventive treatment.

Concerns exist regarding the possibility that widespread use of doxycycline could lead to increased drug resistance, which may undermine its effectiveness in treating infections in the future.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Antibiotic after sex could help curb infections. Cohen, J.[2022]

In a study of 367 patients with Chlamydia trachomatis infections, both doxycycline (100 mg) and spiramycin (1 g) were found to be highly effective, with cure rates of 100% for doxycycline and 98% for spiramycin, indicating that both treatments are viable options.

Spiramycin was associated with a higher incidence of dysethesias in female patients, although these side effects resolved after treatment, suggesting that while effective, further research is needed to explore its safety profile, especially in shorter treatment durations and during pregnancy.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Comparison of spiramycin and doxycycline for treatment of Chlamydia trachomatis genital infections. Dylewski, J., Clecner, B., Dubois, J., et al.[2021]

Doxycycline (Dox) demonstrated significant antiviral activity against vesicular stomatitis virus (VSV) in cultured H1299 cells, inhibiting viral replication in a dose-dependent manner at concentrations of 1.0-2.0 μg/ml.

The antiviral effect of Dox occurs during the early to mid-stages of VSV infection, indicating that it does not affect the virus's ability to enter cells, suggesting potential for Dox in treating viral infections beyond its known antibacterial properties.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Antiviral activity of doxycycline against vesicular stomatitis virus in vitro. Wu, ZC., Wang, X., Wei, JC., et al.[2015]

Citations

1. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC12313191/

Doxycycline post-exposure prophylaxis is effective and ... Doxycycline post-exposure prophylaxis significantly reduced bacterial STI generally, and Chlamydia trachomatis specifically, in a diverse group ...

2. cdc.gov cdc.gov/mmwr/volumes/73/rr/rr7302a1.htm

CDC Clinical Guidelines on the Use of Doxycycline .. ... 200 mg of doxycycline taken within 72 hours after sex has been shown to reduce syphilis and chlamydia infections by >70% and gonococcal infections by ...

3. nature.com nature.com/articles/s41467-025-64261-w

Bacterial sexually transmitted infections and related ... We estimated that doxyPEP would prevent 2.7, 2.5, and 1.4 gonorrhea, chlamydia, and syphilis diagnoses, respectively, per 100 person-years of ...

4. jamanetwork.com jamanetwork.com/journals/jamainternalmedicine/fullarticle/2828994

Doxycycline Postexposure Prophylaxis and Bacterial ... In recent clinical trials, 200-mg doxycycline postexposure prophylaxis (doxyPEP) taken within 72 hours of sex has been shown to reduce the risk ...

5. nejm.org nejm.org/doi/full/10.1056/NEJMoa2211934

Postexposure Doxycycline to Prevent Bacterial Sexually ... The combined incidence of gonorrhea, chlamydia, and syphilis was lower by two thirds with doxycycline postexposure prophylaxis than with standard care.

6. cdc.gov cdc.gov/sti/hcp/doxy-pep/index.html

Doxy PEP for Bacterial STI Prevention Doxy PEP has proven to reduce the risk of getting some bacterial STIs for gay, bisexual, and other men who have sex with men and transgender women at increased ...

7. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC10592014/

Safety of longer-term doxycycline use: A systematic review ... A systematic review of longer-term doxycycline (8+ weeks) found the medication was generally well-tolerated and safe. Findings have implications for doxycycline ...

8. reference.medscape.com reference.medscape.com/drug/vibramycin-doryx-doxycycline-342548

Vibramycin, Doryx (doxycycline) dosing, indications, ... Sexually Transmitted Infections · Lymphogranuloma venereum, uncomplicated urethral, endocervical or rectal infections caused by Chlamydia trachomatis ...

9. mayoclinic.org mayoclinic.org/drugs-supplements/doxycycline-oral-route/description/drg-20068229

Doxycycline (oral route) - Side effects & dosage Doxycycline belongs to the class of medicines known as tetracycline antibiotics. It works by killing bacteria or preventing their growth.