Doxycycline Post-Exposure Prophylaxis (PEP) Dosing Regimen
The recommended dosing regimen for doxycycline post-exposure prophylaxis (PEP) is 200 mg taken as a single dose within 72 hours after potential exposure, not to exceed 200 mg per 24 hours. 1
Indications and Administration
- Doxycycline PEP is recommended by the CDC for gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) with a history of at least one bacterial STI in the past 12 months 1
- The medication should be taken as soon as possible after sexual exposure, but no later than 72 hours 1
- Doxycycline should be taken on a full stomach with a full glass of liquid to prevent gastrointestinal side effects 1
- Patients should avoid lying down for at least 1 hour after taking doxycycline to prevent esophagitis 1
- Doxycycline dose should be separated by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 1
Efficacy and Evidence
- Clinical trials have demonstrated significant reductions in bacterial STIs with doxycycline PEP, including:
- 66% reduction in the combined incidence of gonorrhea, chlamydia, and syphilis compared to standard care 2
- For syphilis specifically, relative risk reductions of 87% in PrEP users and 77% in people living with HIV 2
- For chlamydia, relative risk reductions of 88% in PrEP users and 74% in people living with HIV 2
- For gonorrhea, relative risk reductions of 55% in PrEP users and 57% in people living with HIV 2
Monitoring and Follow-up
- STI screening should be performed at baseline and every 3-6 months at anatomic sites of exposure 1
- The ongoing need for doxy PEP should be assessed every 3-6 months 1
- Monitor for side effects from doxycycline at follow-up visits, including photosensitivity, gastrointestinal symptoms, and esophageal irritation 1
Special Considerations
- For Lyme disease prevention after an Ixodes scapularis tick bite, the same dosing (single 200 mg dose of doxycycline) is recommended within 72 hours of tick removal 1
- Evidence is currently insufficient to make formal recommendations for STI prophylaxis in populations other than MSM and TGW 1
- Longer-term doxycycline use (8+ weeks) is generally safe with mostly minor side effects, though gastrointestinal and dermatological adverse events are more common than with placebo 3
- Chronic alcohol consumption may reduce serum levels of doxycycline, potentially decreasing its efficacy 1
Potential Implementation Strategies
- The most efficient prescribing strategies for doxycycline PEP are based on STI history rather than HIV status or PrEP use 4
- Prescribing doxycycline PEP for 12 months after an STI diagnosis can avert 39% of STI diagnoses with a number needed to treat of 2.4 to prevent one STI 4
- Australian guidelines suggest considering doxycycline PEP primarily for the prevention of syphilis in GBMSM at risk, with secondary benefits for other bacterial STIs 5