**Core Concept**
The management of primary syphilis involves the use of antibiotics to eradicate the causative bacterium, Treponema pallidum. The treatment aims to prevent the progression of the disease and reduce the risk of transmission to others.

**Why the Correct Answer is Right**
The recommended treatment for primary syphilis is a single dose of benzathine penicillin G, administered intramuscularly. This is based on the efficacy of penicillin in killing T. pallidum and the high rate of treatment failure with alternative regimens. The penicillin binds to the bacterial cell wall, inhibiting cell wall synthesis and ultimately leading to the death of the bacteria.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because erythromycin is not the standard treatment for primary syphilis. It may be used in patients with penicillin allergy, but it is not the preferred choice.

**Option B:** This option is incorrect because doxycycline is not effective against T. pallidum. It is used to treat other sexually transmitted infections, such as Lyme disease and chlamydia.

**Option C:** This option is incorrect because ceftriaxone is not the recommended treatment for primary syphilis. While it is effective against many bacterial infections, it is not the standard treatment for syphilis.

**Clinical Pearl / High-Yield Fact**
Remember that patients with syphilis should be tested for HIV and other sexually transmitted infections, as they are more likely to have co-infections.

**Correct Answer:** A. Benzathine penicillin G.