Postexposure prophylaxis (PEP) involves taking a medication to prevent an infection after a possible exposure, a common strategy for preventing HIV. Doxycycline is used as PEP to prevent Lyme disease, and now there is evidence supporting doxycycline as PEP to prevent syphilis, chlamydia, and gonorrhea in specific populations.
Doxycycline is the recommended treatment regimen for chlamydia and an alternative treatment for syphilis in nonpregnant patients with severe penicillin allergy or when penicillin is not available. Although currently not a recommended treatment for gonorrhea because of elevated antimicrobial resistance, doxycycline remains effective against many strains of N. gonorrhoeae in the US.
A recently published CDC MMWR summarizes four studies investigating the efficacy of doxycycline as PEP (doxy PEP) for reducing bacterial STIs among MSM and transgender women (TGW), leading to the following recommendation:
- Providers should counsel all gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) with a history of at least one bacterial sexually transmitted infection (STI) (specifically, syphilis, chlamydia or gonorrhea) during the past 12 months about the benefits and harms of using doxycycline (any formulation) 200 mg once within 72 hours (not to exceed 200 mg per 24 hours) of oral, vaginal, or anal sex and should offer doxycycline postexposure prophylaxis (doxy PEP) through shared decision-making. Ongoing need for doxy PEP should be assessed every 3–6 months. [High-quality evidence supports this strong recommendation to counsel MSM and TGW and offer doxy PEP.]
- No recommendation can be given at this time on the use of doxy PEP for cisgender women, cisgender heterosexual men, transgender men, and other queer and nonbinary persons. [Evidence is insufficient to assess the balance of benefits and harms of the use of doxy PEP.]
The report encourages a number of additional considerations in prescribing doxy PEP:
- Discuss potential harms including doxycycline’s known ADE: photosensitivity, esophagitis, and GI intolerance (nausea, vomiting, and diarrhea)
- Discuss how to mitigate potential ADE: take doxycycline on a full stomach with a full glass of liquid, and avoid laying down for 1 hour after taking doxycycline to prevent esophagitis
- Take doxycycline exactly as prescribed and only for its intended purpose—doses should be taken as soon as possible after sex, but no later than 72 hours later; patients should not take more than 200 mg in 24 hours
- Review potential drug interactions and separate the doxycycline dose by at least 2 hours from dairy products, antacids, and supplements that contain calcium, iron, magnesium, or sodium bicarbonate
- Prescribe enough doses of doxycycline to last until the next follow-up visit, based on individual behavioral assessment and shared-decision making