Doxy PEP

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: 

Source: CDC MMWR, June 2024

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
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