What is the role of intravenous ceftriaxone in the treatment of syphilis?

Role of IV Ceftriaxone in Treatment of Syphilis

IV ceftriaxone serves as an alternative treatment for syphilis, primarily reserved for penicillin-allergic patients or when penicillin is unavailable, with the strongest evidence supporting its use in neurosyphilis at 2 grams daily for 10-14 days.

Primary Indication: Neurosyphilis in Penicillin-Allergic Patients

Ceftriaxone is specifically recommended for neurosyphilis when penicillin cannot be used. The standard regimen is 2 grams daily (IM or IV) for 10-14 days 1, 2. This represents the most established guideline-supported use of ceftriaxone in syphilis treatment.

Critical caveat: Cross-reactivity between ceftriaxone and penicillin exists. If serious concern exists regarding penicillin allergy, skin testing should confirm the allergy before using ceftriaxone, and desensitization with penicillin remains preferred 1, 2.

Early Syphilis (Primary, Secondary, Early Latent)

For early syphilis in penicillin-allergic patients, guidelines acknowledge ceftriaxone as a potential alternative, though with important limitations:

• Dosing: 1 gram daily (IM or IV) for 8-10 days 1
• Evidence quality: Limited clinical studies support this use 1
• Mandatory requirement: Close clinical and serologic follow-up is essential due to inadequate documentation of efficacy 1

The 2022 guideline review 3 provides reassurance with one randomized trial showing comparable efficacy between 1 g/day IV ceftriaxone for 10 days versus benzathine penicillin for early syphilis. However, penicillin desensitization remains the preferred approach when compliance and follow-up cannot be ensured 1.

HIV-Infected Patients

The evidence for ceftriaxone in HIV-infected patients requires particular caution:

• Guidelines explicitly state that ceftriaxone use in HIV-infected persons "has not been studied" and "must be undertaken with caution" 1
• For neurosyphilis in HIV patients, ceftriaxone 2 g daily IV for 10-14 days is considered an "acceptable alternative" when penicillin desensitization is not feasible 4, 5
• Recent research 6 from Mexico (2024) showed comparable early serological response between IV penicillin and ceftriaxone in HIV patients with neurosyphilis, ocular, or otosyphilis (74.4% vs 71.8%, p=0.80)

Ocular and Otosyphilis

Recent research supports ceftriaxone for ocular syphilis:

• A 2024 retrospective study 7 comparing ceftriaxone (2 g IV daily for 14 days) versus aqueous penicillin G in 205 patients found no significant difference in effectiveness (38.2% vs 48.0%, OR 0.672, p=0.301)
• Multiple case series 8, 9, 10 demonstrate successful outcomes with ceftriaxone 2-4 g daily for ocular/otosyphilis
• Practical advantage: Ceftriaxone allows outpatient treatment, avoiding hospitalization required for IV penicillin 7, 8

When NOT to Use Ceftriaxone

Absolute contraindications:

• Neonates ≤28 days requiring calcium-containing IV solutions (risk of fatal precipitation) 11
• Premature neonates up to postmenstrual age 41 weeks 11
• Hyperbilirubinemic neonates (risk of bilirubin encephalopathy) 11
• Pregnancy: Pregnant women with syphilis should be desensitized and treated with penicillin, as penicillin is the only therapy with documented efficacy in pregnancy 1

Treatment Algorithm

For neurosyphilis:

1. First-line: Aqueous crystalline penicillin G 18-24 million units/day IV for 10-14 days
2. If penicillin-allergic: Perform skin testing if available
3. If skin testing confirms allergy or unavailable: Ceftriaxone 2 g daily (IM or IV) for 10-14 days
4. Consider adding benzathine penicillin 2.4 million units IM weekly × 3 weeks after completion to match duration of late syphilis treatment 1, 2

For early syphilis:

1. First-line: Benzathine penicillin G 2.4 million units IM single dose
2. If penicillin-allergic AND compliance/follow-up ensured: Ceftriaxone 1 g daily (IM or IV) for 8-10 days with mandatory close follow-up
3. If compliance uncertain: Desensitize and use penicillin 1

Monitoring Requirements

Regardless of stage treated:

• Serologic follow-up at 3,6,9,12, and 24 months for early syphilis 4, 5
• For neurosyphilis: CSF examination every 6 months until cell count normalizes 2
• Treatment success defined as ≥4-fold decline in nontreponemal titers 4, 5

Key Limitations

The evidence base for ceftriaxone remains substantially weaker than for penicillin. Most guideline recommendations carry lower strength ratings (BIII, CIII) 4, 5, reflecting limited data. The optimal dose and duration have not been definitively established 1. Penicillin remains the gold standard, and ceftriaxone should be viewed as a pragmatic alternative when penicillin is contraindicated or unavailable, not as an equivalent first-line option.