**Question:** Drug of choice for syphilis -

A. Penicillin
B. Azithromycin
C. Erythromycin
D. Tetracycline

**Correct Answer:** A. Penicillin

**Core Concept:** Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. The disease has three stages: primary, secondary, and tertiary. Penicillin is the primary treatment of choice for syphilis, particularly for its early stages.

**Why the Correct Answer is Right:** Penicillin is effective against T. pallidum due to its bactericidal action against Gram-positive bacteria. It penetrates well into tissues, allowing it to treat syphilis successfully in both primary and secondary stages.

**Why Each Wrong Option is Incorrect:**

A. Azithromycin, B. Erythromycin, and D. Tetracycline are all effective against certain bacterial infections, but they are not as potent against Treponema pallidum as Penicillin.

A. Azithromycin is a macrolide antibiotic that targets Gram-positive and some Gram-negative bacteria. It is not as effective against T. pallidum as Penicillin.
B. Erythromycin is another macrolide antibiotic, effective against some Gram-positive bacteria but not as potent against T. pallidum as Penicillin.
D. Tetracycline is a broad-spectrum antibiotic, effective against various Gram-positive and Gram-negative bacteria, but it lacks the potency against T. pallidum as Penicillin.

**Clinical Pearl:** Syphilis treatment should be guided by the stage of the infection and the presence of comorbidities. In cases where Penicillin is contraindicated, TMP-SMX (Trimethoprim-Sulfamethoxazole) can be used as an alternative treatment for syphilis, especially in cases of HIV co-infection. However, Penicillin remains the first-line treatment for syphilis.