Doxy PEP: Plan B for Some Common STIs

You might have already heard about PrEP and PEP (pre and post-exposure prophylaxis), which can help significantly reduce the risk of catching HIV after being exposed to it. If you're like me, you read about these drugs and immediately thought: great, but what about all the other common STIs? Could they have a similar alternative? Well, I am pleased to tell you that recent research reveals that they could—and they do (kind of)! Doxy PEP and PrEP are currently emerging as a “Plan B” option to reduce the risk of catching syphilis, gonorrhea and chlamydia after being exposed. 

First off, let’s distinguish between PEP and PrEP drugs. PEP stands for post-exposure prophylaxis. These drugs need to be taken within 72 hours of exposure to be effective but should be taken as soon as possible to maximize efficiency. PrEP stands for pre-exposure prophylaxis and is a drug taken as a preventative measure daily. 

Doxy PEP, specifically, is a dose of the antibiotic doxycycline, which has been shown to significantly reduce the risk of contracting common bacterial STIs when taken soon after exposure. A study found a 65% reduction in new STI infections among those who took the antibiotic doxycycline within 24-72 hours of exposure. Since doxycycline is an antibiotic, administering this 200mg dose can help prevent the bacteria from multiplying and spreading. Doxy PEP was most effective for chlamydia, cutting new infections by almost 80%. New gonorrhea infections were cut by slightly more than 50%, and some new cases of syphilis were also cut. 

Doxy PEP and the potential it holds as a method against the spread of common STIs comes at a perfect time. STI rates have been steadily increasing in recent years. The US alone reported over 2.5 million STIs in 2021, which reflects a 7% overall increase in STIs between 2017 and 2021 alone. Syphilis has grown at the fastest rate, experiencing a 32% increase between 2020 and 2021 and a 74% increase since 2017! This trend shows little sign of decline. It is important to note that these data are also just based on individuals who have been tested and that, due to stigma, many still do not get tested regularly. What is interesting, too, is that those between the ages of 15 and 24 represent almost half of new infections. The spread of STIs is clearly a significant and growing issue, which—alongside improved sexual education and more accessible, stigma-free testing—needs to be tackled from a new angle. 

Not only are both the quantity and the rate of the spread of common STIs being underestimated, but few know of the true risks untreated STIs pose. Because many of the common STIs do not show any physical symptoms, many individuals will not know of their infected status if they don’t get tested regularly. The most common effects of untreated STIs involve fertility. For those with a uterus, 10-15% of untreated chlamydia cases result in pelvic inflammatory disease; this can result in the swelling and scarring of the fallopian tubes, uterus and ovaries, which in turn can impact fertility. HPV, which is so common that almost every sexually active person carries it at some point, is associated with heightened risks for certain cancers. STIs also decrease the body's immune response, which heightens the risk of catching other infections, including sexually transmitted ones. Untreated STIs can have a significant impact on an individual and their life but also cost the US around $16 billion annually. 

Please don't get too excited, though, as prescribing Doxy PEP as a regular “Plan B” possibility after unprotected sex is still being trialled, and there still remains a lack of overall consensus among doctors, with several not considering this an airtight plan. 

First off, doxy pep is a type of antibiotic, and regular usage of antibiotics can lead to antibacterial resistance. A trial from the US found an 8% increase in resistance levels of the bacteria Staphylococcus aureus among those who took Doxy PEP. Gonorrhea specifically is prone to developing antibiotic resistance; in the US, 1 in 4 gonorrhea cases are resistant to tetracycline, the class of antibiotics of which doxycycline is a part. Obviously, if you have unprotected sex and then end up contracting an STI, you will need antibiotics anyway, so there is an argument for prescribing a PEP dose instead upon exposure to decrease the risk of ever contracting the STI. The concern lies primarily in Doxy PEP as a mainstream healthcare intervention since this is likely to increase the overall usage of antibiotics in the population, which can then result in increased rates of antibiotic resistance. 

The population groups studied so far also limit the generalizability of the conclusions drawn about Doxy PEP. Since the demographics for the two prophylactics largely overlap, many of the trials have been conducted on individuals who already take HIV PrEP. And since research of this sort is still very much emerging within sexuality research, many of the randomized control trials conducted have been smaller pilot studies. 

Another drawback of Doxy PEP, which remains a medical mystery, is that its effects do not extend to cisgender women and transgender men. The first trials from earlier in 2023 do not show any statistically significant results, and thereby, it cannot be concluded that Doxy PEP reduces the rate of new STIs for cisgender women and transgender men who have been exposed. Chlamydia, gonorrhea, and syphilis are more common in cisgender women than cisgender men, which makes these findings very disappointing especially considering how well Doxy PEP works for cisgender men and transgender women. These findings are also interesting, considering that cisgender women and transgender men effectively take antibiotics as a treatment against these common STIs. More research again needs to be conducted to discover why this may be. 

Finally, as with HIV PrEp and PEP, healthcare professionals are concerned that individuals will use these drugs as an alternative for protected sex rather than an emergency option alongside it. Especially at a time when we see rates of STIs and unprotected sex rising, it may be risky to promote alternatives that don’t directly promote protected, safe sex. 

Although it is still too soon to prescribe and recommend Doxy PEP as a large-scale intervention, there is evidence that individuals, particularly MSM (men who have sex with men), take Doxy PEP. More trials are needed, especially ones with larger and more diverse samples, as well as studies that consider the long-term impacts of Doxy PEP. Even though this advancement in sexuality research is exciting, it should be accompanied by comprehensive sexual education, accessible stigma-free testing and the promotion of responsible barrier method sex. While certain questions and worries still remain unanswered, it is undeniable that Doxy PEP could play a pivotal role in the public health approach to STI management. 

Written by Ellen Gisto.