Antibiotic prophylaxis for STIs: Promises or Perils

Comment:

The significant rise in symptomatic and asymptomatic STIs in recent years is having a huge impact on clinical practice. Many practices struggle to manage additional presentations to test and treat those with STI symptoms and to organise treatment and followup of those with positive test results. I have also noted an increase in requests from MSM on PrEP for private Doxycycline scripts for syphilis prophylaxis.

A number of trials are underway to address the topic and it's important to acknowledge that, at present the evidence is minimal. The list of potential adverse consequences is however, a lengthy one.

The rate of HIV resistance in those who acquire HIV while taking PrEP is small..... but we're only focussing on one pathogen. There are numerous bacteria in different organ environments upon which Doxycycline prophylaxis may have an impact. While there are concerns about emerging bacterial resistance in STIs such as Gonorrhoea and Mycoplasma Genitaleum, it is essential that we explore resistance in other organisms at other sites to fully characterise the problem.

Further, intermittent antibiotic use may alter the clinical course of infection (eg Mycoplasma Genitaleum) and partially treat STIs such as syphilis, confusing interpretation of results and management issues further.

The vaginal and penile microbiome have been discussed at several sessions at CROI, and I also wonder what impact antibiotic use may have on such microbiota, and whether this could increase HIV transmission (eg BV being linked to increased transmission)?

This is an important topic and worth understanding some of the complexities so that we can educate individuals seeking prescriptions now, in the absence of evidence.

I've summarised Jean Michel Molina's presentation below:

55 ANTIBIOTIC PROPHYLAXIS FOR STIs: PROMISES OR PERILS

Jean-Michel Molina,

 Globally, more than 1 million STIs are acquired daily, and annually approximately 146 million of new infections with chlamydia, 78 million of gonorrhoea and 6 million of syphilis are diagnosed. In the US, 2015 was the second year in a row with an increase in STIs, with syphilis increasing at an alarming rate among MSM. Implementation of PrEP for HIV prevention has also highlighted the increasing incidence and prevalence of STIs in PrEP users.

 Current efforts to contain the spread of STIs are obviously not sufficient and should include:

              - promotion of condom use.

              - counselling and behavioural interventions.

- vaccinations for viral STIs (Hep A and B, HPV).

- scaling up more effective STI service.

- increased testing for STIs in high risk individuals for early diagnosis of symptomatic and asymptomatic infection.

- better notification and treatment of sex partners.

- new biomedical interventions: Antibiotic prophylaxis?

The success of PrEP for HIV has raised interest in biomedical interventions for STIs. Pending the development of vaccines against bacterial STIs, the potential role of antibiotic prophylaxis should be re-assessed.

Studies conducted by the military have shown the short-term efficacy and the limitations of post-exposure prophylaxis. More recently, periodic presumptive treatment in female sex workers with azithromycin alone or in combination have shown reduction in incidence of gonorrhoea and chlamydia but not of syphilis or HIV. Mass treatment with azithromycin for trachoma and Yaws elimination has also shown some impact on STIs prevalence.

Studies using doxycycline prophylaxis for syphilis in high risk MSM are ongoing. Should antibiotic prophylaxis be successful at reducing STIs incidence, the short-term benefits should be balanced against the potential for adverse consequences:

              Short term reduction in STI prevalence with rebound to pre-intervention rates:

              - Selection of antibiotic resistance.

              - Change in sexual behaviour/risk compensation.

              Changes in STI presentations:

              - Prolongation of the incubation period (delayed seroconversion).

              - More frequent asymptomatic carrier state with extragenital locations.

              - Emergence of new STIs resistant to chemoprophylaxis (eg Mycoplamsa Genitaleum).

              Selection of antibiotic resistance:

              - Selection and clonal dissemination of drug resistant STIs.

              - Reduction of already limited treatment options.

              - Impact on human microbiome: Drug resistance in other pathogens (eg Staph Aureus)

              Tolerability

              Cost

New strategies need to be developed to contain the spread of STIs. Antibiotic prophylaxis for bacterial STIs in high risk populations should be carefully evaluated.