The US Centers for Disease Control and Prevention (CDC) has issued a draft recommendation for health care providers to consider prescribing a single dose of doxycycline, a commonly used antibiotic, to certain people after unprotected sex to prevent the spread of bacterial sexually transmitted infections (STIs) such as chlamydia, gonorrhea, and syphilis. The draft recommendation is based on recent studies that found doxycycline post-exposure prophylaxis (doxyPEP) to be effective in reducing the incidence of these STIs among men who have sex with men (MSM) and transgender women who are living with HIV or are taking HIV pre-exposure prophylaxis (PrEP).

The CDC is seeking public comment on the draft recommendation until November 16, 2023. The final guidelines are expected to be released after the agency reviews the feedback from interested persons and organizations.

CDC Recommends Antibiotic Pill After Sex for Some to Prevent STIs
CDC Recommends Antibiotic Pill After Sex for Some to Prevent STIs

The draft recommendation comes at a time when the rate of STIs is rising across the United States, with more than 2.5 million cases reported in 2021, a jump of 7% in one year. Chlamydia accounted for more than half of those cases, with rates increasing about 4% in 2021. Cases of gonorrhea rose nearly 5%. Cases of syphilis surged 32% in one year, including an alarming rise in infections passed from pregnant mothers to babies developing in the womb.

How Does DoxyPEP Work?

Doxycycline is an antibiotic that is typically used to treat bacterial STIs after someone has been infected. However, recent research suggests that one 200mg dose of the drug also may be effective in preventing such infections if taken within 72 hours after unprotected sex. This method is called doxyPEP, or doxycycline post-exposure prophylaxis.

According to the CDC, doxyPEP works by killing or inhibiting the growth of bacteria that cause chlamydia, gonorrhea, and syphilis before they can establish an infection in the body. DoxyPEP does not protect against other STIs, such as HIV, herpes, or human papillomavirus (HPV), nor does it prevent pregnancy. DoxyPEP also does not treat existing infections or cure latent infections that may reactivate later.

The CDC emphasizes that doxyPEP is not a substitute for regular STI testing and treatment, condom use, or other prevention methods. DoxyPEP is intended to be used as an additional strategy for people who are at high risk of acquiring bacterial STIs and who may not always use condoms or have access to other prevention services.

Who Is Eligible for DoxyPEP?

The CDC’s draft recommendation applies only to MSM and transgender women who are living with HIV or are taking PrEP. These populations have been shown to have higher rates of bacterial STIs than other groups and may benefit from doxyPEP as an adjunctive prevention measure.

To qualify for doxyPEP, a person must have had gonorrhea, chlamydia, or syphilis in the previous year and must report having unprotected sex within the past 72 hours. A person can take doxyPEP up to once per week, but not more than four times per month. A person should not take doxyPEP if they have symptoms of an STI, are allergic to doxycycline or other tetracyclines, are pregnant or breastfeeding, or have certain medical conditions that may interact with doxycycline.

The CDC advises health care providers to counsel their patients about the benefits and risks of doxyPEP, as well as the importance of regular STI testing and treatment, condom use, and other prevention methods. Health care providers should also monitor their patients for adverse effects of doxycycline, such as nausea, vomiting, diarrhea, sun sensitivity, or yeast infections.

What Is the Evidence for DoxyPEP?

The CDC’s draft recommendation is based on two clinical trials that evaluated the efficacy and safety of doxyPEP among MSM and transgender women who are living with HIV or are taking PrEP.

The first trial was conducted in San Francisco and Seattle and involved 554 participants who were randomized to receive either doxycycline or no doxycycline after unprotected sex. The trial was stopped early because it showed that doxyPEP was very effective in preventing bacterial STIs. The results were published in the New England Journal of Medicine in April 2023 and showed that doxyPEP reduced the incidence of gonorrhea, chlamydia, and syphilis by about 65% compared to no doxycycline. DoxyPEP was generally safe and well tolerated by the participants.

The second trial was conducted in Lima, Peru and involved 600 participants who were randomized to receive either doxycycline or placebo after unprotected sex. The trial was completed in September 2023 and the results are expected to be published soon. Preliminary data suggest that doxyPEP was also effective in preventing bacterial STIs in this population, with a similar reduction in incidence as the first trial. DoxyPEP was also safe and well tolerated by the participants.

What Are the Potential Benefits and Risks of DoxyPEP?

The CDC states that doxyPEP has the potential to prevent a substantial number of bacterial STIs among MSM and transgender women who are living with HIV or are taking PrEP, which could reduce the morbidity and mortality associated with these infections, as well as the risk of transmitting them to others. DoxyPEP could also reduce the need for STI treatment and the emergence of antibiotic resistance, which is a growing public health threat.

However, the CDC also acknowledges that doxyPEP has some limitations and uncertainties. For example, doxyPEP may not be effective for all strains of bacteria that cause STIs, especially those that are resistant to doxycycline or other antibiotics. DoxyPEP may also have unintended consequences, such as reducing the natural immunity to STIs, increasing the risk of other STIs or infections, or affecting the gut microbiome or the efficacy of PrEP. DoxyPEP may also have ethical and social implications, such as creating a false sense of security, increasing stigma or discrimination, or affecting sexual behavior or relationships.

The CDC states that more research is needed to address these issues and to evaluate the long-term safety and effectiveness of doxyPEP in different populations and settings. The CDC also urges health care providers and patients to report any adverse events or unexpected outcomes related to doxyPEP to the agency.


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