What are the recommended treatment regimens for syphilis at each stage, including management of neurosyphilis and penicillin‑allergic patients?

Syphilis Treatment Guidelines

Benzathine penicillin G remains the definitive treatment for all stages of syphilis, with stage-specific dosing: single 2.4 million unit IM dose for early syphilis, three weekly 2.4 million unit doses for late latent syphilis, and IV aqueous crystalline penicillin G 18-24 million units daily for 10-14 days for neurosyphilis. 1, 2

Primary and Secondary Syphilis

• Treatment: Benzathine penicillin G 2.4 million units IM as a single dose 1, 2
• This regimen is effective for preventing progression and achieving serological cure in early-stage disease 3
• Follow-up: Quantitative nontreponemal titers should decline fourfold within 6 months after treatment 4

Early Latent Syphilis (< 1 year duration)

• Treatment: Benzathine penicillin G 2.4 million units IM as a single dose 5, 1
• Defined by documented seroconversion, unequivocal symptoms of primary/secondary syphilis within the past year, or sex partner with early syphilis 5

Late Latent Syphilis or Syphilis of Unknown Duration

• Treatment: Benzathine penicillin G 7.2 million units total, administered as three doses of 2.4 million units IM at weekly intervals 5, 1
• CSF examination should be performed if neurologic/ophthalmic symptoms, evidence of tertiary syphilis, treatment failure, or HIV infection with late latent disease 5
• Follow-up: Serologic testing at 6,12, and 24 months; re-evaluate if titers increase fourfold or fail to decline fourfold within 12-24 months 5

Neurosyphilis

Any patient with clinical neurologic involvement (cognitive dysfunction, motor/sensory deficits, cranial nerve palsies, meningitis symptoms) or ocular manifestations requires neurosyphilis treatment regardless of CSF findings. 2

Recommended Regimen

• Aqueous crystalline penicillin G 18-24 million units per day IV, administered as 3-4 million units every 4 hours or continuous infusion, for 10-14 days 2

Alternative Regimen (if compliance assured)

• Procaine penicillin 2.4 million units IM once daily PLUS probenecid 500 mg orally four times daily, both for 10-14 days 2
• Some specialists add benzathine penicillin 2.4 million units IM weekly for 3 weeks after completing neurosyphilis treatment to provide comparable total duration 2

Key Considerations

• Syphilitic uveitis or other ocular manifestations are frequently associated with neurosyphilis and require neurosyphilis treatment 2
• CSF examination should be performed for all patients with ocular disease to identify those requiring follow-up CSF examinations 2
• Intravenous penicillin G is the only adequately studied treatment for neurosyphilis 6, 7

Tertiary Syphilis (Gummatous and Cardiovascular)

• Treatment: Benzathine penicillin G 7.2 million units total, administered as three doses of 2.4 million units IM at weekly intervals 2
• CSF examination should be performed before initiating therapy in symptomatic late syphilis 5, 2
• Some experts treat all cardiovascular syphilis cases with a neurosyphilis regimen 5, 2

Penicillin-Allergic Patients

Primary and Secondary Syphilis (Non-pregnant)

• Doxycycline 100 mg orally twice daily for 14 days OR Tetracycline 500 mg orally four times daily for 14 days 5, 2
• Ceftriaxone shows promise but optimal dose and duration remain undefined 3, 4
• Recent evidence suggests ceftriaxone may have higher serological response rates than penicillin at 6-month follow-up, though more high-quality trials are needed 8

Late Latent Syphilis (Non-pregnant)

• Doxycycline 100 mg orally twice daily for 28 days OR Tetracycline 500 mg orally four times daily for 28 days 5, 2
• These alternatives have limited supporting evidence and require close serologic and clinical follow-up 2

Neurosyphilis and Pregnancy

Penicillin is the only proven effective treatment—desensitization is mandatory for penicillin-allergic patients. 2, 9

• Skin testing to confirm penicillin allergy should be performed before desensitization 5, 10
• No alternative antibiotics have been adequately studied for neurosyphilis 11, 7

Pregnancy

• All pregnant women should be screened serologically for syphilis at the first prenatal visit, during the third trimester (28 weeks), and at delivery 5, 12
• Treatment: Use the penicillin regimen appropriate for the stage of syphilis 5
• Some experts recommend a second dose of benzathine penicillin 2.4 million units IM one week after the initial dose for primary, secondary, or early latent syphilis in pregnancy 5
• Penicillin is the only effective treatment for preventing maternal transmission and treating fetal infection 5, 10
• Pregnant patients allergic to penicillin must be desensitized and treated with penicillin 5, 2

HIV-Infected Patients

Primary and Secondary Syphilis

• Treatment: Benzathine penicillin G 2.4 million units IM single dose (same as HIV-negative patients) 5, 13
• Some experts recommend additional treatments (three weekly doses) though this has not shown enhanced efficacy 13
• Follow-up: Clinical and serologic evaluation at 3,6,9,12, and 24 months 5, 13
• CSF examination and re-treatment should be strongly considered if nontreponemal titers do not decrease fourfold within 6-12 months 5, 13

Latent Syphilis

• Early latent: Benzathine penicillin G 2.4 million units IM single dose 13
• Late latent or unknown duration: Benzathine penicillin G 7.2 million units (three weekly doses of 2.4 million units) 5, 13
• HIV-infected patients with late latent syphilis or syphilis of unknown duration should have CSF examination before treatment 5
• Clinical and CSF abnormalities consistent with neurosyphilis are most likely in HIV-infected persons with CD4 count ≤350 cells/mL and/or RPR titer ≥1:32 13

Special Considerations

• Penicillin regimens should be used for all stages of syphilis in HIV-infected patients 5, 10
• Desensitization is required for penicillin-allergic HIV-infected patients, as alternative regimens are inadequately studied in this population 13

Critical Warnings

• Never administer benzathine penicillin G intravenously or admix with IV solutions—inadvertent IV administration has been associated with cardiorespiratory arrest and death 1
• Injection into or near nerves/arteries can cause permanent neurological damage, transverse myelitis, gangrene, and severe neurovascular complications 1
• Administer by deep IM injection in the upper outer quadrant of the buttock (dorsogluteal) or ventrogluteal site only 1
• Jarisch-Herxheimer reaction may occur with syphilis treatment 1
• Severe cutaneous adverse reactions (Stevens-Johnson syndrome, DRESS, TEN, AGEP) have been reported with penicillin G 1