What is the recommended therapy for syphilis across its stages, including pregnancy and penicillin allergy considerations?

Syphilis Treatment Update

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

Primary and Secondary Syphilis

For early syphilis (primary, secondary, or early latent <1 year duration):

• Single dose of benzathine penicillin G 2.4 million units IM 1, 2
• Treatment success rates: 90-100% 3

Penicillin Allergy (Non-Pregnant)

• Doxycycline 100 mg orally twice daily for 14 days (preferred alternative) 4, 1
• Tetracycline 500 mg orally four times daily for 14 days 4, 1
• Erythromycin 500 mg orally four times daily for 14 days (less effective, use only if compliance assured) 4
• Ceftriaxone regimens may be considered but optimal dosing undefined; single-dose therapy is NOT effective 4, 5

Critical caveat: Alternatives to penicillin have limited clinical data and should be used with close serologic follow-up 1

Latent Syphilis

Early Latent (<1 year)

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

Late Latent or Unknown Duration

• Benzathine penicillin G 7.2 million units total: three doses of 2.4 million units IM at weekly intervals 1, 2

Important: If a dose is missed, intervals of 10-14 days between doses may be acceptable for non-pregnant patients, but pregnant women must restart the entire course 1

Penicillin Allergy (Non-Pregnant)

• Doxycycline 100 mg orally twice daily for 28 days 1
• Tetracycline 500 mg orally four times daily for 28 days 1
• Must use with close serologic and clinical follow-up 1
• Efficacy in HIV-infected persons not well studied 1

Tertiary Syphilis (Gumma/Cardiovascular)

• Benzathine penicillin G 7.2 million units total: three doses of 2.4 million units IM at weekly intervals 1
• CSF examination required before treatment if symptomatic 1
• Cardiovascular syphilis may warrant neurosyphilis regimen; consult infectious disease specialist 1

Neurosyphilis

Any patient with neurologic symptoms (cognitive dysfunction, motor/sensory deficits, cranial nerve palsies, meningitis), ophthalmic manifestations (uveitis, neuroretinitis, optic neuritis), or auditory symptoms requires CSF examination 1

Recommended Regimen

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

Alternative (if compliance ensured)

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

Key consideration: Some specialists add benzathine penicillin G 2.4 million units IM weekly for up to 3 weeks after completing neurosyphilis treatment to provide comparable total duration 1

Pregnancy

Penicillin is the ONLY proven effective treatment for preventing maternal-fetal transmission and treating fetal infection 5, 1, 6

Treatment Protocol

• Use the penicillin regimen appropriate for the stage of syphilis 5, 1
• All pregnant women with penicillin allergy MUST be desensitized and treated with penicillin 4, 1, 5, 1
• No alternative antibiotics are acceptable in pregnancy 5, 1

Additional Considerations

• Some experts recommend a second dose of benzathine penicillin G 2.4 million units IM one week after initial dose for primary, secondary, or early latent syphilis 5, 1
• First dose should be administered in labor and delivery with continuous fetal monitoring for at least 24 hours due to Jarisch-Herxheimer reaction risk (occurs in up to 44% of pregnant women) 6
• Jarisch-Herxheimer reaction can cause contractions, fetal heart rate abnormalities, and stillbirth in severely affected pregnancies 5, 1, 6
• Ultrasound findings of fetal syphilis (hepatomegaly, hydrops, ascites) indicate higher risk for treatment failure; manage with obstetric specialists 5, 1, 6

Screening Requirements

• First prenatal visit 5, 1
• 28 weeks gestation 5, 1
• At delivery 5, 1
• Any stillbirth after 20 weeks 5, 1

HIV-Infected Patients

Early Syphilis

• Treat as HIV-negative patients with benzathine penicillin G 2.4 million units IM single dose 5, 1
• More intensive follow-up required: 6,12,18, and 24 months 5, 1

Late Latent or Unknown Duration

• CSF examination required before treatment 5, 1
• If CSF normal: benzathine penicillin G 2.4 million units IM weekly for 3 weeks 5, 1
• If CSF abnormal: treat as neurosyphilis 5, 1

Treatment Failure Criteria

• Clinical symptoms develop 5, 1
• Nontreponemal titers rise fourfold 5, 1
• Titers fail to decline fourfold within 6-12 months 5

Action: Perform CSF examination and re-treat; most experts use 7.2 million units benzathine penicillin G (three weekly doses) if CSF normal 5, 1

Follow-Up Monitoring

Early Syphilis

• Quantitative nontreponemal tests at 6 and 12 months 1
• Serologic response should be evident by 6 months 3

Late Latent Syphilis

• Quantitative nontreponemal tests at 6,12, and 24 months 1
• Serologic response generally slower (12-24 months) 3

Re-treatment Indications

• Titers increase fourfold 1
• Initially high titer (≥1:32) fails to decline at least fourfold within 12-24 months 1, 7
• Signs or symptoms attributable to syphilis develop 1

Serofast state: Some patients remain seropositive with low stable titers despite adequate treatment; clinical significance unclear, but additional therapy or CSF examination may not be needed if titers remain stable and low 1, 3

Critical Warnings

Administration

• FOR DEEP INTRAMUSCULAR INJECTION ONLY 2
• DO NOT inject intravenously or admix with IV solutions - associated with cardiorespiratory arrest and death 2
• Do not inject into or near arteries or nerves - can cause permanent neurological damage, gangrene, transverse myelitis with paralysis 2
• Inject in upper outer quadrant of buttock (dorsogluteal) or ventrogluteal site 2
• Anterolateral thigh NOT recommended due to adverse effects 2

Severe Reactions

• Anaphylaxis can occur; have epinephrine, oxygen, IV steroids, and airway management immediately available 2
• Severe cutaneous adverse reactions (Stevens-Johnson syndrome, TEN, DRESS, AGEP) reported 2
• Clostridioides difficile-associated diarrhea possible with any antibacterial 2

Common Pitfalls

1. Using non-penicillin regimens in pregnancy - absolutely contraindicated; desensitization is mandatory 5, 1, 8
2. Single-dose ceftriaxone - NOT effective for syphilis 4, 5
3. Inadequate follow-up - essential to detect treatment failure and reinfection 1
4. Missing doses in pregnant women - requires restarting entire course 1
5. Not performing CSF examination in HIV patients with late latent syphilis - required before treatment 5, 1
6. Treating neurosyphilis with benzathine penicillin - requires IV aqueous crystalline penicillin G 1
7. Ignoring ocular symptoms - syphilitic uveitis requires neurosyphilis treatment regimen 1