A 26-year-old man has a painless genital ulcer for 2 weeks. VDRL is reactive at 1:32; TPHA is positive. Dark-field microscopy of exudate shows motile corkscrew-shaped organisms with 6–14 regular spiral coils. The drug of choice for early syphilis is:

• A Doxycycline 100 mg BD for 28 days
• B Azithromycin 2 g single dose
• C Ceftriaxone 1 g IM for 10 days
• D Benzathine penicillin G 2.4 million units IM single dose ✓

Explanation

Dark-field microscopy demonstrating T. pallidum (corkscrew morphology with regular coils, 0.1–0.2 × 6–20 µm, slow forward rotation with backward flexion), combined with reactive VDRL and TPHA, confirms primary/early syphilis. Benzathine penicillin G 2.4 MU IM as a single dose remains the treatment of choice for primary, secondary, and early latent syphilis per WHO/CDC guidelines — T. pallidum has never developed penicillin resistance. Doxycycline 100 mg × 14 days is the alternative for penicillin-allergic non-pregnant patients. Azithromycin resistance (A2058G 23S rRNA mutation) has been reported globally and is not recommended. Ceftriaxone is an alternative but not first-line.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.