Doxycycline Post-Exposure Prophylaxis Dosing
The recommended dose for doxycycline post-exposure prophylaxis (doxy PEP) is 200 mg taken 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
Target Population
- Doxy PEP is specifically recommended for gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) who have had at least one bacterial STI (gonorrhea, chlamydia, or syphilis) diagnosed in the past 12 months 1, 2
- Evidence is currently insufficient to recommend doxy PEP for cisgender women or heterosexual men 2
Dosing Details and Administration
- Timing: Take as soon as possible after sexual exposure, but no later than 72 hours post-exposure 1, 2
- Formulation: Any doxycycline formulation at 200 mg total dose 1
- Frequency limitation: Do not exceed 200 mg in any 24-hour period, even with multiple sexual encounters 1, 2
- Food requirements: Take on a full stomach with a full glass of liquid 1, 2
- Posture precaution: Avoid lying down for at least 1 hour after taking to prevent esophagitis 1, 2
Drug Interactions and Timing Considerations
- Separate doxycycline dose by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 1, 2
- No clinically relevant interactions with gender-affirming hormonal therapy 1
- Review all medications (including over-the-counter) for potential interactions 1
Prescription Quantity and Follow-Up
- Prescribe enough doses based on the individual's anticipated sexual activity until their next visit 1
- Reassess ongoing need for doxy PEP every 3-6 months 1, 2
- Perform STI screening (gonorrhea, chlamydia, syphilis) at baseline and every 3-6 months at anatomic sites of exposure 1, 2
Efficacy Data
The evidence supporting this dosing comes from high-quality randomized controlled trial data showing doxy PEP reduces bacterial STI incidence by approximately two-thirds overall 3, 4:
Common Side Effects to Counsel Patients About
- Photosensitivity (sun sensitivity) 1, 2
- Gastrointestinal symptoms: nausea (15.4%), vomiting (5.8%), diarrhea 1, 5
- Esophagitis and esophageal discomfort 1, 2
- Potential for antimicrobial resistance development in other pathogens 1
Critical Pitfall to Avoid
Do not confuse doxy PEP dosing (200 mg single dose) with standard treatment dosing for active STIs (typically 100 mg twice daily for 7-14 days). 6, 7 The PEP regimen is specifically a one-time prophylactic dose, not a treatment course.