PrEP for STIs – Is biomedical STI prevention within our reach?

By Chris Williams, updated 3 weeks ago in Health / Sexual health

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We’ve seen remarkable success with HIV PrEP — a previously unimaginable way of using medicine to prevent HIV. But the question arises: can a similar pill prevent STIs? The answer is yes, and it offers new hope for addressing the escalating STI epidemic.

In less than a decade, Australia has gone from being barely aware of PrEP as a biomedical HIV prevention strategy to it being broadly available as a government-subsidised medicine. PrEP’s rapid and widespread uptake by gay and bi+ guys is testament to its desirability and convenience as a highly effective addition to the HIV prevention toolkit.

But as is rightly pointed out in healthy discussions, PrEP only offers protection against HIV. It doesn’t protect against other STIs.

Of course, PrEP is much more than just a pill; it’s a strategy for managing sexual health, which incorporates comprehensive HIV and STI testing every 3 months. While estimates predict that more people on PrEP could reduce STIs in the long run, testing alone is just part of the “prevent, test, treat” mantra of health organisations.

There are different ways to use PrEP to suit different needs. Our PrEP Selector tool helps identify the best PrEP option, whatever your circumstances.

Innovative interventions: Condoms, antibiotics and vaccines

The more we learn about how STIs are transmitted, the more apparent it’s becoming we urgently need additional approaches for preventing them — the mighty condom has its strengths but also its limitations.

One such limitation is the recent discovery that saliva could be the main driver of gonorrhea transmission — kissing is estimated to account for nearly three-quarters of all cases of gonorrhea in men who have sex with men. And we know from research that few of us are enthused to prevent oral transmission by refraining from a good pash.

“…kissing is estimated to account for nearly three-quarters of all cases of gonorrhea in men who have sex with men.”

While we patiently await the development of STI vaccines, enter broad-spectrum antibiotic doxycycline.

Promising results: Doxycycline prevents some STIs

It’s natural to feel concerned after hearing media warnings about the potential dangers of unnecessary antibiotic use. You might think twice before gobbling down more of them. Being cautious about how we use biomedical technologies isn’t a bad thing. But neither is using the tools we have safely and responsibly, following guidance from expert medical professionals.

For nearly a century, doctors have relied on antibiotics to treat STIs — a practice pioneered by Alexander Fleming, who discovered the first antibiotic in 1928. However, using antibiotics proactively to prevent STIs is a relatively new field of study.

But the evidence indicating doxycycline provides promising protection against STIs is mounting.

Inititially, a small pilot study in 2015 involving 30 people living with HIV found that participants given doxycycline were 70 per cent less likely to acquire an STI than those financially incentivised to use other forms of STI prevention.

A second study took place in 2016 involving 232 HIV-negative men and trans women — the results showed that using doxycycline demonstrated a risk reduction of 70 per cent for syphilis and 73 per cent for chlamydia. However, it didn’t show any risk reduction for gonorrhea.

More recently, the US DoxyPEP study from 2022 showed that using the antibiotic after sex (as a post-exposure prophylaxis, or PEP) cut STIs by 66 per cent overall. Interestingly, this method worked really well for preventing chlamydia and syphilis and also showed more than a 50 per cent risk reduction for gonorrhea — something earlier studies hadn’t observed. One of the possible reasons for this concerns whether the gonorrhea strains already had some resistance to doxycycline.

While the evidence base for biomedical STI prevention grows, the San Francisco Department of Health has already issued guidance to healthcare providers on prescribing Doxy PEP to eligible patients. The San Francisco AIDS Foundation now leads the US in adopting this new strategy in an effort to curb the spread of STIs as an urgent public health priority.

More recently, in March 2024, the Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM) created a concensus statement with preliminary guidance for clinicians, community, researchers and policy makers. In short, it suggests that ‘doxy-PEP’ (doxycycline used as PEP, after sex) should be considered primarily for the prevention of syphilis in gay, bi+ and other men who have sex with men who are at risk of this STI, with a secondary benefit of reductions in other bacterial STIs.

Legitimate concerns: Doxycycline side effects and antimicrobial resistance

So far, the study results are promising, especially for syphilis and chlamydia. Chlamydia continues to be the most commonly diagnosed STI in Australia. And between 2012 and 2021, infectious syphilis incidence increased among HIV-negative gay and bisexual men by 53 per cent and by 33 per cent among HIV-positive gay and bisexual men.

So, does that mean we should all start chowing down on doxycycline as soon as we can? No — but it does yield hope for the possibility of adding an extra tool to the STI prevention toolkit. Because right now, other than physical barrier devices such as condoms and dams, we don’t have many other options to prevent STIs.

“Being cautious about how we take advantage of biomedical technologies isn’t a bad thing.”

Despite promising results, there are legitimate concerns with using antibiotics this way. In theory, regular and widespread population use of an antibiotic could lead to antimicrobial resistance — meaning the very STIs we’re trying to prevent could become drug-resistant infections that are not treatable with those particular antibiotics. While that could limit possible treatment options, resistance to one type of antibiotic doesn’t mean resistance to all antibiotics. Other treatment options may still exist, but the levels and types of antimicrobial resistance are things our clinical experts monitor carefully.

Furthermore, while doxycycline is typically well-tolerated by most people, it can increase photosensitivity (skin sensitivity to sunlight) and cause possible stomach upsets. With Australia known for having one of the highest skin cancer rates in the world, it’s certainly a consideration for anyone wondering if this could be right for them.

That said, it’s also important to consider that the benefits of reducing the risk of getting chlamydia or syphilis potentially outweigh the harms of some people using doxycycline intermittently. Rather than using doxycycline every day, recent studies had participants take just 200mg (two pills) within 72 hours after sex.

The takeaway

These developments make it seem as if the dawn of biomedical STI prevention could be within our reach. For the time being, using antibiotics to prevent STIs remains a considered choice for discussion between you and your doctor. Legitimate concerns from medical professionals must be explored in more detail, along with community attitudes towards the possibility of adding another pill to what is already a sizeable dose to swallow for some of us.

And although fears about antimicrobial resistance are real, we don’t yet fully know the effects a roll-out of biomedical STI prevention might have. This uncertainty might feel uncomfortable, but bear in mind that the possibility of massively curbing the spread of STIs also exists in this realm. Not only would this be of substantial personal benefit to gay and bisexual men, but it could also mean using far fewer of these precious antibiotic resources overall — a massive drop in circulating STIs would mean fewer STI cases to treat with antibiotics. After all, prevention is better than cure, no?

Doxycycline may offer some promise as an additional tool for preventing STIs, but it won’t be right for everyone. Commentary from clinicians suggests it would likely be more suited to highly sexually active people with multiple partners who may not always use condoms.

“…right now, other than physical barrier devices such as condoms, we just don’t have many effective ways to prevent STIs.”

If we’ve learned anything from the immense success of PrEP for HIV, it’s that biomedical solutions don’t just help protect us at a cellular level. They can also protect us at an emotional level, safeguarding us from fear and fostering our confidence to connect with one another. And doesn’t everyone have the right to enjoy sex without worry?

Until we’re sure about who might use doxycycline and when, we suggest using a simple latex tool — otherwise known as a condom — as the best way to help prevent most of these unwanted infections.