Drug of choice for primary syphilis is
**Core Concept**
The question is testing the knowledge of the recommended treatment for primary syphilis, a sexually transmitted infection caused by the bacterium *Treponema pallidum*. The treatment involves antibiotics that target the causative organism.
**Why the Correct Answer is Right**
The drug of choice for primary syphilis is **Benzathine Penicillin G** (BPG). This long-acting penicillin formulation provides a sustained release of penicillin, allowing for a single dose treatment to effectively cure the infection. BPG works by inhibiting the bacterial cell wall synthesis through the inhibition of transpeptidase enzymes, ultimately leading to bacterial lysis and death.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while doxycycline is an alternative treatment for syphilis in patients allergic to penicillin, it is not the drug of choice for primary syphilis.
**Option C:** This option is incorrect because ceftriaxone is not the recommended treatment for primary syphilis; it is used for gonorrhea treatment.
**Clinical Pearl / High-Yield Fact**
When treating syphilis, it's essential to note that patients should be tested for HIV and other sexually transmitted infections (STIs) simultaneously, as syphilis can increase the transmission and acquisition of other STIs.
**Correct Answer: B. Benzathine Penicillin G**