A 28-year-old man presents with a painless indurated genital ulcer for 3 weeks. VDRL is reactive (titre 1:32), TPHA is positive, and FTA-ABS is positive. He had a penicillin allergy (anaphylaxis) in childhood. The best treatment alternative for primary syphilis is:

• A Ceftriaxone 1 g IM daily for 10 days
• B Azithromycin 2 g single dose
• C Erythromycin 500 mg QID for 15 days
• D Doxycycline 100 mg BD for 14 days ✓

Explanation

For penicillin-allergic patients with primary or secondary syphilis (non-pregnant), doxycycline 100 mg twice daily for 14 days is the CDC-recommended alternative. Azithromycin 2 g was previously used but is no longer recommended due to widespread macrolide resistance in Treponema pallidum (A2058G and A2059G mutations). Erythromycin has poor efficacy. Ceftriaxone has limited evidence and is not formally recommended as primary alternative for syphilis in penicillin-allergic patients. Penicillin desensitisation is the preferred approach in pregnancy.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.