Doxycycline for STD Prevention: Recommended Dosing
The recommended dose of doxycycline for sexually transmitted disease prevention 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, 2
Target Population
The CDC specifically recommends doxycycline post-exposure prophylaxis (doxy-PEP) for:
- Gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) who have had at least one bacterial STI (syphilis, chlamydia, or gonorrhea) diagnosed in the past 12 months 1, 2
- This represents a Strength AI recommendation (strong recommendation, high-quality evidence) from the 2024 CDC guidelines 1
- 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, 3
Dosing Protocol
Single-dose regimen:
- 200 mg doxycycline (any formulation) taken once within 72 hours after sexual exposure 1, 2, 4
- Take as soon as possible after sex, but no later than 72 hours 1
- Maximum dose: 200 mg per 24 hours, even if multiple sexual encounters occur 1, 2
- Prescribe enough doses based on anticipated sexual activity until the next visit 2
Expected Efficacy
Doxy-PEP demonstrates significant protective effects:
- Syphilis and chlamydia: >70% reduction 1, 3
- Gonorrhea: approximately 50% reduction 1, 3
- Meta-analysis confirms reduced incidence of first STI (HR 0.538,95% CI 0.337-0.859) and specifically chlamydia (RR 0.291,95% CI 0.093-0.911) 5
Critical Administration Instructions
To prevent esophagitis and optimize absorption:
- Take with a full glass of water (at least 200 mL) 1, 2
- Take on a full stomach with non-dairy food 1, 2
- Remain upright for at least 1 hour after taking the medication 1, 2
- Separate from dairy products, antacids, calcium, iron, magnesium, or sodium bicarbonate by at least 2 hours before AND after dosing to prevent chelation and treatment failure 2
Monitoring and Follow-up
Reassess every 3-6 months:
- Perform STI screening at all anatomic sites of exposure (oral, rectal, urogenital) 1, 3
- Serologic testing for syphilis 1
- HIV screening per CDC HIV PrEP guidelines 1
- Assess for doxycycline side effects 1
- Reassess ongoing need for doxy-PEP 1, 2
Comprehensive Sexual Health Approach
Doxy-PEP should be implemented alongside:
- Counseling on condom use and partner reduction 1
- HIV PrEP/PEP as indicated 1
- Risk reduction counseling at follow-up visits 1
Common Side Effects and Precautions
Counsel patients on:
- Photosensitivity: Recommend sun protection measures 2, 3
- Gastrointestinal symptoms: Nausea, vomiting, diarrhea 1, 3
- Esophagitis risk: Prevented by proper administration technique 1, 3
- Chronic alcohol consumption may reduce serum doxycycline levels 1
Critical Pitfalls to Avoid
- Do not exceed 200 mg in 24 hours, even with multiple sexual encounters 1, 2
- Do not use incorrect dosing: Real-world data shows 21% of users who reported using doxyPEP used a dosage other than the recommended 200 mg 6
- Do not take with dairy products: This causes chelation and can lead to treatment failure and antimicrobial resistance 2
- Do not prescribe for populations without evidence: Current data supports use only in MSM and TGW with recent bacterial STI history 1