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

By Chris Williams, updated 8 months ago in Health / Sexual health

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Previously unimaginable HIV prevention is already an unprecedented success with the help of HIV PrEP. But could there be a pill to prevent STIs? Yes, there are new hopes in sight for curbing the rising STI epidemic…

In just a few years, Australia has gone from being barely aware of PrEP as a biomedical HIV prevention strategy to being available nationwide as a government-subsidised medicine. PrEP’s rapid and widespread uptake by gay and bisexual men is a 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 offers extremely good protection against HIV. It just doesn’t protect against other STIs.

Of course, PrEP is much more than just a pill. It’s a comprehensive strategy for managing sexual health and well-being, which includes routine HIV and STI testing every three months. While scientific modelling estimates predict that more people using PrEP would likely reduce STIs in the long run, testing alone is only part of the “prevent, test, treat” mantra of health agencies.

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 relatively 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 protects against some STIs

Now, it’s understandable that after seeing media hype about an impending apocalypse from non-essential antibiotic use, you might be a little apprehensive about gobbling down more of them. Being cautious about how we utilise biomedical technologies isn’t a bad thing. But neither is using the tools we have safely and responsibly under guidance from expert medical professionals.

We’ve been using antibiotics to treat STIs for almost a hundred years. Thanks, Alexander Fleming — the discoverer of the first antibiotic in 1928. But using them to prevent STIs proactively is still a young science.

So far, a handful of studies involving doxycycline have shown promising results for offering some protection against STIs.

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

The 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 is whether or not the gonorrhea strains circulating among study participants already had some level of 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.

Legitimate concerns: Doxycycline side effects and antimicrobial resistance

These results are promising, especially for chlamydia and syphilis. 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. However, for now, using antibiotics to prevent STIs remains under careful investigation. 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 a clinical recommendation comes in for using doxycycline or any other innovative developments in STI prevention, we still suggest using a simple latex tool — otherwise known as a condom — as the best way to help prevent most of these unwanted infections.