JOHN YANG: There's a promising new way to prevent the spread of some sexually transmitted infections and it uses an old drug, a cheap and widely available antibiotic.

Laura Barron-Lopez has more.

LAURA BARRON LOPEZ: A morning after pill for sexually transmitted infections.

A single dose of the antibiotic doxycycline taken in the hours immediately after sex could stop bacterial STIs like chlamydia, gonorrhea and syphilis.

It's a potential game changer in the fight against transmitted infections one that's more urgent now with a sharp rise in cases over the last decade.

But some health officials are raising concerns that wider use of the preventative antibiotic could breed drug resistance.

For more on the preventative strategies potential and risks, we turn to Washington Post journalist Fenit Nirappil.

Thanks so much for joining us explain this new protocol, which is known as DoxyPEP.

FENIT NIRAPPIL, The Washington Post: So it's doxycycline, which is a common antibiotic.

And it's used as a post exposure prophylaxis.

So the idea is that if you administer this antibiotic, and if someone takes the pills, up to 72 hours after having sex, it can reduce their chances of contracting a bacterial STI, like chlamydia, syphilis and gonorrhea.

LAURA BARRON LOPEZ: And so STI is have increased some 30 percent over the last five years.

Syphilis is at its highest level in the last 70 years.

So do public health officials really believe that this could totally change the game?

FENIT NIRAPPIL: So public health officials have been saying they really need new tools, promoting condoms, promoting abstinence, it can only go so far.

And so they've been looking for medical interventions as well, really, the big hope is getting something like a vaccine, but there hasn't really been much progress on that front.

So to something like DoxyPEP gives you an option to get it to the highest risk populations.

And then if people who are at the highest risk for STIs aren't getting it, you stop the chains of transmission early, and then you can prevent broader circulation of STIs.

LAURA BARRON LOPEZ: And a number of populations across the board are seeing an increase in STIs.

But public health officials right now are targeting the use of this DoxyPEP among transgender women and men who have sex with men.

Why just targeted on those populations?

FENIT NIRAPPIL: So those were the populations that were studied in the research that found DoxyPEP effective.

And the reason you're looking at gay men are more precisely men who have sex with men and trans women is because rates of STIs are higher in that group.

And I also want to be clear, one of the reasons here is not just because of differences in sexual behavior, but because when you have a smaller pool of people, and a smaller pool of sexual partners, when one person has an STI, it's easier for that STI to spread.

So the idea here is that they want to limit DoxyPEP to people who are at highest risk, because DoxyPEP, as you mentioned earlier can also have unintended consequences and that's because it's an antibiotic.

In the medical profession, you want to try and limit the use of antibiotics, because it can lead to drug resistance, both for individuals and for the population as a whole.

LAURA BARRON LOPEZ: So could you explain that argument a bit more, because as you know, there are some doctors who are concerned about the use of doxycycline, more and more, and the fact that it could potentially breed drug resistant superbugs.

So what's their argument there, and what our public health officials saying in response to that?

FENIT NIRAPPIL: So the argument is that if you're using an antibiotic like doxycycline, dozens of times a year, you can be facilitating the rise of drug resistant superbugs.

Because as the bacteria that cause diseases like syphilis, gonorrhea, and chlamydia are circulating, you might facilitate the evolution of bugs that can overcome antibiotics like doxycycline.

And then you might have a situation where people are contracting strains of these bacteria, and the frontline treatments are no longer effective.

And that's at the population level.

At the individual level, there's also a worry that using antibiotics regularly can make it harder for that antibiotic to be effective when you're sick with other issues.

Or it might harm your gut microbiome health, because there are healthy bacteria in our systems too that promote good health and antibiotic like doxycycline can really wipe that bacteria out.

LAURA BARRON LOPEZ: But doxycycline has been used in other for other reasons, right?

And have they seen any type of drug resistance when it's used for other treatments?

FENIT NIRAPPIL: Yes, and that's one of the really important issues here.

So doxycycline is not a new morning after pill.

It's an old pill that just has a new use.

This antibiotic is used for Lyme's disease.

It's used for long term acne treatment.

It's used for malaria prevention.

And so some of the promoters of doxycycline as STI prevention say that it's being held to an unfair standard.

And they're also wondering here if part of the discomfort is that this is really for gay sexual health.

And because it is allows people to have sex without condoms, without having to worry as much about STIs.

LAURA BARRON LOPEZ: Some doctors aren't comfortable with that?

FENIT NIRAPPIL: The concern here is our doctors being hesitant to help people avoid STIs because they see the antibiotic is unnecessary, because people who work in the sexual health field says we have to acknowledge the reality that not everyone is going to wear condoms.

And condoms also aren't 100 percent effective against STIs especially if you're not wearing them consistently or properly.

So in the sexual health field you have a real demand for alternatives to condoms and abstinence.

But in the broader medical field you have a real concern about antibiotics.

And the CDC is actually drafting guidelines for how to distribute DoxyPEP right now.

And that's the exact kind of conundrum that they're trying to address.

How do you deal with the problem of rising STIs and how do you also avoid the problem of antibiotic resistance and making it worse.

LAURA BARRON LOPEZ: Fenit Nirappil of The Washington Post, thank you so much for your time.

FENIT NIRAPPIL: Thanks so much for having me.