A 32-year-old woman is evaluated for a maculopapular rash on her trunk and palms, generalized lymphadenopathy, and condyloma lata. Serology shows RPR 1:64 (positive), FTA-ABS positive, and TP-PA positive. She is 18 weeks pregnant. What is the most appropriate next step in management?

## Clinical Scenario Analysis This is a case of **secondary syphilis** (rash, lymphadenopathy, condyloma lata) in a **pregnant woman** at 18 weeks gestation. Serological confirmation is robust (RPR, FTA-ABS, TP-PA all positive). ## Treatment Algorithm for Syphilis in Pregnancy ```mermaid flowchart TD A[Syphilis diagnosed in pregnancy]:::outcome --> B{Penicillin allergy?}:::decision B -->|No allergy| C[Benzathine PCN G 2.4 MU IM weekly × 3 weeks]:::action B -->|Allergy present| D{Anaphylaxis?}:::decision D -->|No anaphylaxis| E[Penicillin desensitization, then PCN]:::action D -->|Anaphylaxis| F[Azithromycin 500 mg daily × 21 days]:::action C --> G[Repeat serology at delivery]:::action E --> G F --> G G --> H[Treat neonate if maternal titers elevated]:::action ``` ## Antibiotic Regimens in Pregnancy | Stage of Syphilis | Non-Pregnant | Pregnant (No Allergy) | Pregnant (Allergic) | |---|---|---|---| | **Primary/Secondary** | Benzathine PCN G 2.4 MU IM once | Benzathine PCN G 2.4 MU IM **weekly × 3 weeks** | Azithromycin 500 mg daily × 21 days (or desensitization + PCN) | | **Early latent** | Benzathine PCN G 2.4 MU IM once | Benzathine PCN G 2.4 MU IM weekly × 3 weeks | Azithromycin 500 mg daily × 21 days | | **Late latent/Tertiary** | Benzathine PCN G 2.4 MU IM weekly × 3 weeks | Benzathine PCN G 2.4 MU IM weekly × 3 weeks | Azithromycin (less reliable) or desensitization | ## Key Point **Key Point:** Penicillin is the **only reliably effective agent** for preventing congenital syphilis. In pregnancy, the dose and frequency are **higher and more frequent** than in non-pregnant patients: **Benzathine PCN G 2.4 MU IM weekly for 3 weeks** (total 7.2 MU) is standard for primary, secondary, or early latent syphilis. ## Why NOT Doxycycline? **Warning:** Doxycycline is **teratogenic** (causes permanent tooth discoloration and enamel hypoplasia in the fetus if given after 15 weeks gestation). It is absolutely contraindicated in pregnancy, regardless of trimester. ## Why NOT Azithromycin as First-Line? **Clinical Pearl:** Although azithromycin is an acceptable alternative in penicillin-allergic pregnant women, it is **NOT first-line** in a non-allergic patient. Azithromycin also has lower cure rates (~90%) and does not reliably prevent congenital syphilis compared to penicillin. Reserve it for documented penicillin allergy. ## High-Yield **High-Yield:** The **3-week regimen** (weekly dosing) in pregnancy differs from the single-dose regimen in non-pregnant patients. This higher cumulative dose ensures adequate placental transfer and fetal protection. Failure to use the 3-week regimen increases risk of congenital syphilis and adverse fetal outcomes. ## Serological Follow-Up Repeat RPR/VDRL at delivery. If titers remain ≥1:8 or rise 4-fold, treat the neonate with aqueous penicillin G IV or IM for 10 days.