Doxycycline is NOT a Pre-Exposure Prophylaxis (PrEP) Medication for STIs
Doxycycline is recommended as postexposure prophylaxis (PEP), not pre-exposure prophylaxis (PrEP), for bacterial sexually transmitted infections. The CDC explicitly distinguishes between these two approaches: PEP involves taking medication after a possible exposure, while PrEP involves taking medication before exposure occurs 1.
Key Distinction Between PEP and PrEP
- Postexposure prophylaxis (PEP) is the CDC-recommended approach for doxycycline in STI prevention, where 200 mg is taken within 72 hours after sexual exposure 1, 2.
- Pre-exposure prophylaxis (PrEP) involves taking medication before exposure occurs, which is NOT the current CDC recommendation for doxycycline in STI prevention 1.
Limited Evidence for Doxycycline as STI PrEP
While doxycycline has been studied as PrEP for other infections (malaria, Lyme disease), the evidence for STI PrEP is minimal 1:
- Only one small 2015 trial studied daily doxycycline 100 mg as STI PrEP in 30 MSM with HIV, showing a 73% reduction in bacterial STI incidence 1.
- Since 2015, there have been no new studies of STI PrEP, and the 2021 CDC STI treatment guidelines concluded that further studies were necessary before recommending this approach 1.
- The CDC has not issued recommendations supporting doxycycline as PrEP for STI prevention 1.
Current CDC Recommendation: Doxy-PEP Only
The CDC recommends doxycycline postexposure prophylaxis (doxy-PEP) for MSM and transgender women who have had a bacterial STI diagnosed in the past 12 months 1, 2:
- Dose: 200 mg taken once within 72 hours after oral, vaginal, or anal sex 1, 2.
- Maximum frequency: Not to exceed 200 mg per 24 hours 1, 2.
- Efficacy: Reduces syphilis and chlamydia by >70% and gonorrhea by approximately 50% 1, 3.
Clinical Context
The terminology matters clinically because:
- Doxy-PEP is event-driven (taken after sex), making it more targeted and reducing overall antibiotic exposure compared to daily dosing 2, 4.
- PrEP would imply daily dosing before exposure, which raises greater concerns about antimicrobial resistance and is not supported by current evidence for STI prevention 1, 5.
- For populations other than MSM and TGW, evidence is currently insufficient to make formal recommendations for either PrEP or PEP 2.
Monitoring Requirements for Doxy-PEP
When prescribing doxy-PEP (not PrEP), patients require 1, 2:
- STI screening at baseline and every 3-6 months at anatomic sites of exposure.
- Reassessment of ongoing need every 3-6 months.
- HIV screening for HIV-negative individuals according to current recommendations.