The preferred drug treatment for all stages of syphilis is:

Rationale: A. Ciprofloxacin is a fluoroquinolone antibiotic that is generally ineffective against Treponema pallidum, the spirochete responsible for syphilis. While it has broad-spectrum activity against many Gram-negative bacteria, it does not reach therapeutic concentrations for syphilis eradication. Using this agent would result in treatment failure and the potential progression of the infection to neurosyphilis. B. Parenteral Penicillin G remains the definitive treatment of choice for all stages of syphilis because the causative organism has not developed resistance to this antibiotic. The formulation and duration vary by stage; primary and secondary syphilis typically require a single intramuscular dose. Its bactericidal action effectively destroys the cell walls of the spirochetes, preventing the long-term systemic complications of the disease. C. Azithromycin has been used as an alternative for syphilis treatment, but high rates of resistance have been documented in many geographic regions. It is not considered first-line therapy because of the increased risk of treatment failure compared to penicillin. It should only be used in specific circumstances where penicillin is contraindicated and other alternatives are not feasible. D. Acyclovir is an antiviral medication used exclusively to treat viral infections such as herpes simplex and varicella-zoster. Syphilis is a bacterial infection caused by a spirochete and does not respond to antiviral agents. Misdiagnosing syphilis as a viral lesion and treating it with acyclovir would allow the bacterial infection to spread systemically without being checked.