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PREP,PEP, and DOXYPEP

DoxyPEP (Doxycycline)

Doxycycline is an antibiotic that has been in use since the 1960s. It is also known as Vibramycin-D, Efracea, and Periostat. Doxycycline is a 'bacteriostatic' that inhibits the growth of bacteria but doesn't kill them directly. Amoxicillin (an antibiotic you may be more familiar with) is 'bactericidal', which directly kills the bacteria. It is available on the NHS to treat many bacterial infections, such as chest infections and rosacea (a skin condition).

Although prophylaxis (prevention) against STIs has a long history, dating back to the First World War, the two most important studies were the US DoxyPEP Study in San Francisco and Seattle and the DOXYVAC study in Paris. Following promising trials in the USA and France, Doxycycline (or DoxyPEP) is also being touted as a preventative measure against STIs - a "morning-after pill" to prevent chlamydia, gonorrhoea and syphilis.

"The UK National Guideline for the Use of DoxyPEP for the Prevention of Syphilis provides healthcare professionals with a clear, evidence-informed framework for prescribing doxyPEP to those at increased risk of syphilis – a serious and rising challenge within the UK’s sexual health landscape. The latest data from the UK Health Security Agency (UKHSA) shows that syphilis diagnoses in England increased by almost 5% over the past year, reaching their highest recorded level since 1948."

BASHH publishes UK-first guidelines on doxyPEP for the prevention of syphilis | BASHH | 9 Jun 2025

While there remain concerns that the potential benefits of DoxyPEP are outweighed by the risk of developing antibiotic resistance in STIs and other bacteria, BASHH says the new guideline "will support clinicians and patients to feel confident about the use of doxyPEP, balancing antimicrobial stewardship with better sexual health outcomes." All good then.

Dissent on doxyPEP: recent guidelines becoming more cautious | NAM aidsmap | 24 Apr 2024
Two recent statements about taking the antibiotic doxycycline up to 72 hours after sex to prevent bacterial sexually transmitted infections, a prevention intervention known as doxyPEP, are notably more cautious about recommending its use than the first guidelines from California.

Doxycycline | NHS
Doxycycline | Wikipedia
Doxycycline | National Institute for Health and Care Excellence (NICE)
Using antibiotics to prevent STIs | nam aidsmap
DoxyPEP: the future of STI prevention? | Love Tank
NHS and local government to roll out world-first vaccine programme to prevent gonorrhoea | NHS England

CDC to recommend antibiotic after sex for some to prevent STIs | CBS News | 4 Oct 2023 | 3m 51s
AIDS 2022: Antibiotics to prevent STIs | aidsmap | 1 Aug 2022 | 2m 13s

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