Syphilis is a serious sexually transmitted infection caused by the bacterium Treponema pallidum. If the infection is not properly treated, it can progress through several stages, potentially leading to severe complications affecting the brain, heart, and other organs. Diagnosis and treatment must always be overseen by a qualified healthcare professional to ensure the infection is eradicated and to prevent serious long-term health consequences.
Standard Treatment for Syphilis
The first-line treatment for all stages of syphilis is Penicillin G, an antibiotic highly effective against T. pallidum. The specific formulation used is Benzathine Penicillin G, administered via intramuscular injection. This delivery method is critical for treatment success.
This therapy relies on achieving and maintaining a sustained, low concentration of the drug in the bloodstream, known as the treponemicidal level. Benzathine Penicillin G is formulated for slow release over several days or weeks, ensuring continuous exposure. This prolonged exposure is necessary because T. pallidum divides very slowly, and penicillin is only effective against actively dividing cells.
The recommended dosage is 2.4 million units per injection, given deep into the muscle. The frequency of injections varies based on the infection stage. This injectable therapy provides the reliable, sustained concentration needed to eradicate the infection.
Why Amoxicillin is Not the Primary Treatment
Oral antibiotics, including Amoxicillin, are not considered primary treatment for syphilis because they fail to meet the pharmacological requirements. Syphilis requires the treponemicidal concentration to be maintained for several days or weeks. Oral Amoxicillin is rapidly absorbed and excreted, making it impossible to sustain the necessary blood level over the required duration.
This inability to maintain a consistent concentration increases the risk of treatment failure, meaning the bacteria may not be fully eliminated. Inadequate treatment allows the infection to progress silently to later stages, including neurosyphilis. Treatment protocols prioritize total eradication to prevent damage to the central nervous system.
In rare contexts, such as penicillin allergy where desensitization is not an option, alternative oral regimens like Amoxicillin combined with probenecid have been explored. Probenecid inhibits the kidney’s ability to excrete penicillin-like drugs, thereby boosting the Amoxicillin concentration. However, this specialized approach is not the standard recommendation.
Determining Treatment Length Based on Stage
The duration of standard syphilis treatment depends entirely on the stage of the infection. Syphilis is categorized into distinct stages, and the length of treatment reflects the bacterial load and the time required for the antibiotic to reach affected tissues. The shortest regimen is reserved for early syphilis (primary, secondary, and early latent stages).
For early syphilis, the standard treatment is a single 2.4 million unit dose of Benzathine Penicillin G administered as one intramuscular injection. This single dose is sufficient because the infection is localized and the bacteria are actively dividing, making them most susceptible.
Treatment for late latent syphilis, tertiary syphilis, or latent syphilis of unknown duration requires a prolonged course spanning three weeks. This regimen consists of three separate 2.4 million unit injections of Benzathine Penicillin G, given at weekly intervals. The longer duration is necessary because bacteria in these later stages divide more slowly or may be sequestered in difficult-to-reach tissues.
A more intensive protocol is required for neurosyphilis or ocular syphilis. These conditions require hospitalization and the administration of Aqueous Crystalline Penicillin G intravenously for 10 to 14 days. This ensures high antibiotic levels rapidly penetrate the central nervous system.
Post-Treatment Monitoring and Follow-Up
Patients must undergo regular post-treatment monitoring to confirm the cure. This follow-up relies on serological monitoring, using nontreponemal tests such as the RPR or VDRL, to measure antibody levels in the blood. For early syphilis, these tests are repeated at six and twelve months after therapy completion.
A successful response is defined by a significant drop in the antibody titer, typically a fourfold decrease within 6 to 12 months. For example, a drop from 1:32 to 1:8 is considered an adequate response. If the titer fails to drop appropriately, or if it increases fourfold, it may indicate treatment failure or reinfection.
Patients successfully treated often have persistently low, positive antibody titers, a state known as being “serofast.” These low levels do not indicate active infection but require documentation to prevent unnecessary retreatment. Follow-up also includes the notification and testing of sexual partners to prevent disease spread and minimize reinfection risk.