What is the recommended treatment regimen for syphilis, including considerations for penicillin allergy, pregnancy, and neurosyphilis?

Treatment of Syphilis

Benzathine penicillin G remains the definitive treatment for all stages of syphilis, with stage-specific dosing, and penicillin desensitization is mandatory for pregnant patients with penicillin allergy—no alternatives are acceptable in pregnancy. 1, 2

Primary and Secondary Syphilis

Recommended regimen:

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

This achieves 90-100% treatment success rates in early syphilis 3. The single-dose approach is well-established, though some specialists recommend additional doses in HIV-infected patients (see below).

Follow-up

• Repeat quantitative nontreponemal tests at 6 and 12 months 1
• Treatment failure indicators:
  • Fourfold increase in titers
  • Failure of titers to decline fourfold within 6 months
  • Persistent or recurrent symptoms 1
• Re-treatment requires CSF examination to exclude neurosyphilis before administering 3 weekly doses of benzathine penicillin G 1

Latent Syphilis

Early latent (<1 year duration):

• Benzathine penicillin G 2.4 million units IM single dose 1

Late latent (>1 year or unknown duration):

• Benzathine penicillin G 7.2 million units total: 2.4 million units IM weekly for 3 consecutive weeks 1

Critical consideration

If a patient misses a dose during the 3-week regimen, intervals of 10-14 days between doses may be acceptable—except in pregnancy, where the entire course must be restarted 1.

Tertiary Syphilis (Gumma/Cardiovascular)

• Benzathine penicillin G 7.2 million units total: 2.4 million units IM weekly for 3 weeks 1
• CSF examination is mandatory before treatment if symptomatic 1
• Cardiovascular syphilis may warrant neurosyphilis regimen; consult infectious disease specialist 1

Neurosyphilis

This is the most critical distinction—neurosyphilis requires IV therapy, not IM benzathine penicillin.

Recommended regimen:

• Aqueous crystalline penicillin G 18-24 million units/day IV (3-4 million units every 4 hours or continuous infusion) for 10-14 days 1

Alternative regimen (if compliance assured):

• Procaine penicillin 2.4 million units IM daily PLUS probenecid 500 mg orally four times daily, both for 10-14 days 1

Important nuance

Because neurosyphilis regimens are shorter than late syphilis treatment, some specialists add benzathine penicillin G 2.4 million units IM weekly for 3 weeks after completing the neurosyphilis regimen 1.

Ocular syphilis

Syphilitic uveitis or any ocular manifestation must be treated as neurosyphilis with CSF examination and the full IV penicillin regimen 1, 4.

Follow-up

• Repeat CSF examination every 6 months until cell count normalizes 1
• If CSF not improved at 6 months or not normal at 2 years, re-treat 1

Penicillin Allergy

Non-pregnant patients

Early syphilis alternatives:

• Doxycycline 100 mg orally twice daily for 14 days, OR
• Tetracycline 500 mg orally four times daily for 14 days 1
• Ceftriaxone 1 gram IM or IV daily for 8-10 days (limited data) 1
• Azithromycin 2 grams orally single dose (preliminary data only, use with caution) 1

Late latent/tertiary syphilis alternatives:

• Doxycycline 100 mg orally twice daily for 28 days, OR
• Tetracycline 500 mg orally four times daily for 28 days 1
• These require close serologic and clinical follow-up; efficacy in HIV-infected persons is unproven 1

Neurosyphilis alternative:

• Ceftriaxone 2 grams IM or IV daily for 10-14 days (cross-reactivity with penicillin possible) 1

Pregnant patients

There are NO acceptable alternatives to penicillin in pregnancy. 5, 1, 2

• Pregnant women with penicillin allergy MUST undergo penicillin desensitization and then receive the stage-appropriate penicillin regimen 5, 1, 2
• Erythromycin does not reliably cure fetal infection 5
• Tetracyclines are contraindicated (hepatotoxicity, fetal bone/teeth staining) 2
• Azithromycin and ceftriaxone lack sufficient safety/efficacy data in pregnancy 2

Pregnancy-Specific Considerations

Screening

• Test at first prenatal visit 2
• Repeat at 28-32 weeks gestation and at delivery in high-risk populations 2
• Test all women delivering stillborn infants after 20 weeks 5, 2

Treatment approach

• Use the stage-appropriate penicillin regimen 5, 6, 2
• Some experts recommend a second dose of benzathine penicillin G 2.4 million units IM one week after the initial dose for women with primary, secondary, or early latent syphilis, particularly in the third trimester 5, 6, 2

Jarisch-Herxheimer reaction

• Occurs in up to 44% of pregnant women 7
• Can precipitate preterm labor, fetal distress, or stillbirth 5, 2, 7
• Recommendation: Administer first dose of benzathine penicillin G in labor and delivery with continuous fetal monitoring for 24 hours in viable pregnancies 7
• Subsequent doses can be given outpatient 7

Ultrasound evaluation

• Perform pretreatment ultrasound when feasible in viable pregnancies >20 weeks 7, 8
• Findings suggesting fetal infection (hepatomegaly, placentomegaly, elevated MCA-PSV, ascites, hydrops) indicate higher risk of treatment failure and complications 2, 7, 8
• Abnormal ultrasound warrants specialist consultation 2, 8

Follow-up

• Check titers monthly to ensure no fourfold increase (suggests reinfection/treatment failure) 2, 7
• Rate of titer decline does not predict pregnancy outcomes 7

HIV-Infected Patients

HIV-infected patients may have increased risk of neurologic complications and treatment failure, though the magnitude is likely minimal 1.

Primary/secondary syphilis:

• Benzathine penicillin G 2.4 million units IM single dose 1
• Some specialists recommend additional treatments (e.g., 3 weekly doses or adding neurosyphilis regimen), though evidence is limited 1

Latent syphilis:

• CSF examination recommended before treatment for late latent syphilis or unknown duration 6
• If CSF normal: benzathine penicillin G 7.2 million units (3 weekly doses) 6
• If CSF abnormal: treat as neurosyphilis 6

Enhanced follow-up:

• Evaluate at 3-month intervals (instead of 6-month) 1
• At 6-12 months, if titers don't decline fourfold, perform CSF examination and re-treat 6

Critical caveat: Alternative non-penicillin regimens have not been studied in HIV-infected persons and must be used with extreme caution 1.

Common Pitfalls

1. Treating ocular syphilis with IM benzathine penicillin—this is inadequate; requires IV neurosyphilis regimen 1, 4

2. Using alternatives to penicillin in pregnancy—absolutely contraindicated; desensitization is mandatory 5, 1, 2

3. Not performing CSF examination when indicated—required for symptomatic late syphilis, HIV-infected patients with late latent disease, treatment failures, and any neurologic/ocular symptoms 1, 6, 5

4. Inadequate follow-up—serologic monitoring is essential to detect treatment failure or reinfection 1

5. Confusing "serofast" state with treatment failure—persistent low titers (<1:8) after adequate treatment with appropriate initial decline may not require re-treatment 7, 3