From the Guidelines
For prophylactic syphilis treatment when IM penicillin G is unavailable, doxycycline 100 mg orally twice daily for 14 days is the recommended alternative. This regimen is effective for early syphilis (primary, secondary, or early latent syphilis of less than one year's duration) 1. For patients with penicillin allergy, this oral option provides good coverage against Treponema pallidum, the bacterium that causes syphilis. If you're pregnant, doxycycline should be avoided; instead, you would need desensitization to penicillin as no adequate oral alternatives exist during pregnancy 1. It's essential to complete the full course of treatment and follow up with serological testing to ensure the infection has been adequately treated. Doxycycline works by inhibiting bacterial protein synthesis, effectively stopping the growth and spread of the spirochete.
Some key points to consider:
- Azithromycin as a single 2-g oral dose has been effective for treating early syphilis in some settings, but its use is not recommended in the United States due to Treponema pallidum chromosomal mutations associated with azithromycin resistance and treatment failures 1.
- Ceftriaxone (intravenous or intramuscular; 1 g/d for 10 days) is a reasonable alternative treatment for early syphilis 1.
- There is insufficient evidence to recommend oral amoxicillin plus probenecid for the treatment of syphilis 1.
- Sexual partners should also be evaluated and treated appropriately to prevent reinfection.
The most recent and highest quality study, published in 2022, supports the use of doxycycline as an acceptable alternate option for treating early and late latent syphilis if penicillin cannot be used 1.
From the Research
Oral Penicillin Dose for Prophylactic Syphilis Treatment
If intramuscular (IM) penicillin G is not available, the following oral penicillin doses can be considered for prophylactic syphilis treatment:
- There is no direct evidence of oral penicillin dose for prophylactic syphilis treatment. However, studies have compared the efficacy of oral antibiotics such as azithromycin and doxycycline with benzathine penicillin G for the treatment of syphilis 2, 3, 4, 5.
- Azithromycin has been shown to be effective in treating early syphilis, with a single 2.0-g dose or two 2.0-g doses given 1 week apart achieving a cumulative response rate of 94% and 83%, respectively 2.
- Doxycycline has also been used as a second-line treatment for syphilis, with a 14-day course of 100 mg twice daily achieving a serological treatment success rate of 82.9% 5.
- It is essential to note that these studies were conducted for the treatment of syphilis, not prophylaxis, and the efficacy of oral penicillin for prophylactic syphilis treatment is not well established.
Considerations for Oral Penicillin Use
When considering oral penicillin for prophylactic syphilis treatment, the following points should be taken into account:
- The efficacy and safety of oral penicillin for prophylactic syphilis treatment have not been extensively studied.
- The use of oral antibiotics such as azithromycin and doxycycline may be considered as an alternative to penicillin, but their efficacy for prophylaxis is not well established 2, 3, 4, 5.
- The choice of antibiotic and dosage should be guided by the specific clinical scenario and the patient's medical history, and should be made in consultation with a healthcare professional.