Doxycycline Post-Exposure Prophylaxis (Doxy PEP) Dosing
For STI prevention, take doxycycline 200 mg as a single dose within 72 hours after condomless oral, vaginal, or anal sex, with a maximum of 200 mg per 24-hour period. 1, 2
Recommended Dosing Protocol
The CDC-recommended regimen is:
- 200 mg doxycycline (any formulation) taken once within 72 hours after sexual exposure 1, 2
- Take as soon as possible after exposure, but no later than 72 hours 1
- Do not exceed 200 mg in any 24-hour period 1, 3
Who Should Receive Doxy PEP
The CDC strongly recommends doxy PEP for:
- Gay, bisexual, and other men who have sex with men (MSM) with at least one bacterial STI (syphilis, chlamydia, or gonorrhea) diagnosed in the past 12 months 1, 2
- Transgender women (TGW) with at least one bacterial STI in the past 12 months 1, 2
Evidence is currently insufficient to recommend for or against doxy PEP in cisgender women, cisgender heterosexual men, transgender men, and other queer and nonbinary persons. 1 A randomized trial in Kenyan cisgender women showed no significant reduction in STI incidence (relative risk 0.88,95% CI 0.60-1.29, P=0.51), with low adherence detected on hair sample analysis (29% detection rate). 4
Administration Instructions to Minimize Side Effects
To prevent esophagitis and gastrointestinal upset:
- Take on a full stomach with at least 200 mL (full glass) of water 1, 5
- Remain upright for at least 1 hour after taking the medication 1, 5
- Separate doxycycline by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 1
Expected Efficacy
Doxy PEP reduces:
Monitoring Requirements
Baseline and ongoing assessments should include:
- STI screening at all anatomic sites of exposure (oral, rectal, urogenital) at baseline and every 3-6 months 1, 2
- Serologic testing for syphilis every 3-6 months 1
- HIV screening per CDC HIV PrEP guidelines 1, 2
- Reassess ongoing need for doxy PEP every 3-6 months 1, 2
- Monitor for side effects including photosensitivity, gastrointestinal symptoms, and esophagitis 1, 2
Important Caveats
Antimicrobial resistance concerns: Doxy PEP use over 6 months increases the proportion of tetracycline resistance genes in the gut resistome from 46% to 51% in the metagenome and from 4% to 15% in the metatranscriptome, with higher doxycycline exposure correlating with greater tetracycline resistance gene enrichment. 7 However, no significant increases in non-tetracycline resistance gene classes were observed, and gut microbiome diversity remained unchanged. 7
This is not a replacement for comprehensive sexual health: Doxy PEP should be implemented alongside condom counseling, partner reduction strategies, and HIV PrEP/PEP as indicated. 1, 2
Common side effects include: Photosensitivity (advise sun protection), gastrointestinal intolerance (nausea, vomiting, diarrhea), and esophagitis (prevented by proper administration technique). 1, 2