What is the recommended treatment for a patient with latent syphilis?

Treatment of Latent Syphilis

For early latent syphilis (infection acquired within the past year), administer benzathine penicillin G 2.4 million units IM as a single dose; for late latent syphilis or latent syphilis of unknown duration, administer benzathine penicillin G 7.2 million units total as three doses of 2.4 million units IM at weekly intervals. 1, 2

Defining the Stage of Latent Syphilis

Before initiating treatment, you must determine whether the patient has early versus late latent syphilis, as this dictates the treatment regimen:

• Early latent syphilis is defined as infection acquired within the preceding year, documented by: 1, 2

  • Documented seroconversion within the past year
  • Fourfold increase in nontreponemal titer within the past year
  • History of symptoms of primary or secondary syphilis within the past year
  • Having a sex partner with documented early syphilis

• Late latent syphilis includes all other cases where infection duration exceeds one year or is unknown 1, 2

Pre-Treatment Evaluation: When to Perform Lumbar Puncture

You must perform a CSF examination before treatment if the patient meets ANY of the following criteria: 1, 2

• Neurologic signs or symptoms (meningitis, cognitive dysfunction, motor deficits, hearing loss)
• Ophthalmic manifestations (uveitis, iritis, vision changes)
• Evidence of active tertiary syphilis (aortitis, gumma, iritis)
• Treatment failure (previous treatment with inadequate serologic response)
• HIV infection with late latent syphilis or syphilis of unknown duration
• Serum nontreponemal titer ≥1:32, unless duration of infection is known to be <1 year 3, 2

If CSF shows abnormalities consistent with neurosyphilis, treat with aqueous crystalline penicillin G 18-24 million units per day IV for 10-14 days instead of the latent syphilis regimen 2

Treatment Regimens for Adults

Early Latent Syphilis

• Benzathine penicillin G 2.4 million units IM as a single dose 3, 1, 2

Late Latent Syphilis or Latent Syphilis of Unknown Duration

• Benzathine penicillin G 7.2 million units total, administered as three doses of 2.4 million units IM at 1-week intervals 3, 1, 2

The CDC guidelines consistently recommend this three-dose regimen across multiple iterations, making it the definitive standard of care 3, 1, 2. If a patient misses a dose during weekly therapy, an interval of 10-14 days between doses might be acceptable before restarting the sequence, though this should not be considered acceptable for pregnant patients who must repeat the full course if any dose is missed 3, 1

Treatment for Penicillin-Allergic Patients

Non-Pregnant Adults

Critical caveat: Alternative regimens should only be used after CSF examination has excluded neurosyphilis 3, 2

For early latent syphilis:

• Doxycycline 100 mg orally twice daily for 14 days 3, 1, 2, 4
• Alternative: Tetracycline 500 mg orally four times daily for 14 days 3, 2

For late latent syphilis or unknown duration:

• Doxycycline 100 mg orally twice daily for 28 days 3, 1, 2, 4
• Alternative: Tetracycline 500 mg orally four times daily for 28 days 3, 2

The effectiveness of these alternatives has not been well documented, and they should be used only with close serologic and clinical follow-up 3. The efficacy in HIV-infected persons has not been studied and must be considered with caution 3

Pregnant Patients

Pregnant patients who are allergic to penicillin MUST undergo desensitization followed by penicillin treatment—there are no acceptable alternatives. 3, 1, 2 Penicillin is the only therapy with documented efficacy for preventing maternal transmission to the fetus and treating fetal infection 1. Alternatives like tetracycline, doxycycline, erythromycin, azithromycin, and ceftriaxone are inadequate, as erythromycin does not reliably cure fetal infection 1

Pediatric Dosing

After the newborn period, children diagnosed with syphilis should have a CSF examination to exclude neurosyphilis, and birth and maternal medical records should be reviewed to assess whether the child has congenital or acquired syphilis 3, 2

For early latent syphilis:

• Benzathine penicillin G 50,000 units/kg IM, up to the adult dose of 2.4 million units in a single dose 3, 2

For late latent syphilis or unknown duration:

• Benzathine penicillin G 50,000 units/kg IM, up to the adult dose of 2.4 million units, administered as three doses at 1-week intervals (total 150,000 units/kg up to adult total dose of 7.2 million units) 3, 2

Follow-Up Protocol

Quantitative nontreponemal serologic tests (RPR or VDRL) should be repeated at 6,12, and 24 months after treatment. 3, 1, 2 This is critical for detecting treatment failure.

Criteria for Re-Treatment

Re-treat the patient and evaluate for neurosyphilis if ANY of the following occur: 3, 1, 2

• Titers increase fourfold (two dilutions)
• An initially high titer (≥1:32) fails to decline at least fourfold within 12-24 months of therapy
• Signs or symptoms attributable to syphilis develop

Re-treatment typically involves three weekly injections of benzathine penicillin G 2.4 million units IM, unless CSF examination indicates neurosyphilis 1. In rare instances, despite a negative CSF examination and repeated course of therapy, serologic titers may still not decline—in these circumstances, the need for additional therapy or repeated CSF examinations is unclear 3

Special Considerations for HIV-Infected Patients

HIV-infected patients should receive the same penicillin regimens as non-HIV-infected patients 1. However, closer follow-up is mandatory to detect potential treatment failure or disease progression 1. Patients with HIV infection and late latent syphilis or syphilis of unknown duration should have a prompt CSF examination 3, 2. Those with penicillin allergy should undergo skin testing and desensitization, then be treated with penicillin 1

Management of Sex Partners

Persons exposed within 90 days preceding the diagnosis of primary, secondary, or early latent syphilis should be treated presumptively even if seronegative. 1 Persons exposed >90 days before diagnosis should be treated presumptively if serologic test results are not immediately available and follow-up is uncertain 1

Critical Pitfalls to Avoid

• Do not use azithromycin in the United States due to widespread macrolide resistance and documented treatment failures 1
• Do not use oral penicillin preparations for syphilis treatment as they are ineffective 1
• Do not switch between different nontreponemal tests (e.g., VDRL and RPR) when monitoring serologic response, as results cannot be directly compared 1
• Do not rely solely on treponemal test antibody titers to assess treatment response, as they correlate poorly with disease activity 1
• Remember that 15-25% of successfully treated patients remain "serofast" with persistent low titers (<1:8) that do not indicate treatment failure 1

Jarisch-Herxheimer Reaction

Patients should be informed about the Jarisch-Herxheimer reaction, an acute febrile reaction that may occur within 24 hours after any syphilis therapy, especially in early syphilis 1. This may include headache, myalgia, fever, and other symptoms 1. Pregnant women treated during the second half of pregnancy are at risk for premature labor and/or fetal distress from this reaction and should seek immediate medical attention if they notice contractions or changes in fetal movements 1