Antimicrobial Resistance in Antibiotic Treatment and Prevention of Sexually Transmitted Diseases

In early 2022, antibiotic prophylaxis was introduced in San Francisco to reduce sexually transmitted bacterial diseases such as chlamydia, syphilis and gonorrhea. Two early studies showed that this prophylaxis was effective and could reduce infection rates. Since then, further extensive studies have been carried out, primarily confirming this assumption. With the introduction of prophylaxis, questions also arose. Does antimicrobial resistance increase? Does prophylaxis damage the microbiome? Even though we do not yet have definitive answers to either question, let’s take a look at what we know and where we still need to learn more.
April 25, 2024

What is antimicrobial resistance?

Antimicrobial resistance means that a microbe, such as a bacterium, continues to multiply despite exposure to an active substance (antibiotic) that is lethal to it. The bacteria defend themselves through various mechanisms: For example by transporting the antibiotic out of the bacterial cells by pumps, rendering the antibiotic harmless with enzymes or through genetic mutations.

“Antibiotic prophylaxis only works if the STIs are not yet resistant. It is therefore important to use it responsibly and always keep an eye on possible new resistances so that it continues to work.”

When does antimicrobial resistance occur?

When bacteria are exposed to an antibiotic and survive because the treatment is too short or the dosage too low, they often exchange protective mechanisms with each other. This development of resistance varies greatly between bacterial species. While gonococci (gonorrhea bacteria) quickly become resistant to almost all antibiotics, syphilis and chlamydia have shown a rather slow adaptation and are not prone to developing resistance to the drugs currently used to treat them in humans.

What does this have to do with antibiotic STI prophylaxis?

Antibiotic STI prophylaxis also involves taking an antibiotic at irregular intervals, which is effective against a variety of bacteria and sometimes also parasites. There is now concern that resistance to these pathogens could develop and spread, which could impair the effectiveness of antibiotics for other infections and individuals.

What does research say about the long-term use of antibiotics in therapy and prophylaxis?

The antibiotics used for STI prophylaxis have also been used continuously for years for both acute and chronic diseases. The occurrence of resistance is not a new phenomenon in this context and has been investigated in numerous studies. An earlier review evaluating the suitability of antibiotics for the prophylaxis of STIs found that “low and transient” resistance was predominantly observed (Truong R et al. 2023; doi:10.1093/jacamr/dlac009).

Even in the two large ongoing studies in the US and in France, only a moderate development of resistance has been observed to date. New data from 2024 also suggest that resistance develops depending on the frequency of use and that the effect on the composition of the microbiome also appears to be very small (V.T. Chu et al. CROI 2024; Abst. 1154).

Does it make sense to use antibiotic prophylaxis for STIs despite possible resistance?

The “test-and-treat” strategy has not achieved the hoped-for global success in the fight against sexually transmitted bacterial infections; infection rates are stagnating or even rising noticeably. In addition, safer sex education is becoming less effective as the fear of HIV diminishes.

An important turning point in the US was the introduction of antibiotic post-exposure prophylaxis. As predicted, this first-of-its-kind measure quickly led to a significant decrease in chlamydia and syphilis infections in communies with consistent use. This is confirmed by recent data from San Francisco showing a strong decline in these STIs (Scott H et al., CROI 2024 #126; Bacon O et al., CROI 2024 #1151, Cohen S, CROI 2024 #37).

Antibiotic post-exposure prophylaxis is an extremely effective method of prevention that currently carries only a low risk of developing resistance. Considering its use is therefore not only justified, but also coincides with a strong interest in this method within communities with a high STI risk. It would be unacceptable to withhold this effective and well-tolerated option from this risk group.

“Taking antibiotic STI prophylaxis as rarely as necessary, but consistently and in the right situation, can be a useful addition to prevention!”

What should be considered with regard to resistance during use?

If symptoms occur despite taking antibiotic prophylaxis, the use should be discontinued immediately and a test for STIs should be carried out. Continued use could otherwise increase the risk of resistance.In order to maximize benefits and lower risks, prophylaxis should also only be used if there is a particular risk of STIs. In this respect, antibiotic STI prophylaxis differs fundamentally from HIV-PrEP, which must always be taken consistently. Of course, as with HIV-PrEP, STI testing should always be carried out immediately if symptoms occur in order to maintain both your health and the effectiveness of the treatment.

A dry look at the resistance debate

Why do we take a more rational approach to the often critically viewed use of antibiotics in many areas of medicine and veterinary medicine, while antibiotic STI prophylaxis triggers an emotional debate - even though it only concerns a small part of the population? Are there sometimes other motives behind the pronounced skepticism towards this method than just the risk of resistance? Could latent homophobia, personal ideas of “the right way of having sex” or the rejection of a biomedically-optimized lifestyle play a role?

These questions cannot be answered conclusively. However, it is important to keep them in mind in order to find a balance between community needs and medical aspects.

Medication can help reduce your risk for bacterial STIs*

* If indicated by a doctor