This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti Microbial, Subject name: Pharmacology
Drug of choice for primary syphilis is 
Select and explain. 
A. Ampicillin, B. Benzathine penicillin, C. Erythromycin, D. Tetracycline
B: Benzathine penicillin
Answer: B: Benzathine penicillin 
Explanation: Ans. b (Benzathine penicillin). (Ref. Pharmacology KD Tripathi 5th/657, 673, 688; Harrison's Medicine 16th/980)Rx of SyphilisEarly & latent syphilisLate syphilis1.2 MU Procaine penicillin x 10 daysOR2.4 MU benzathine penicillin 1-3 weeklyBenzathine penicillin2.4 MU weekly for 4 weeksDrug used for treatment of syphilis# Penicillin# Erythromycin# Tetracycline# Cephalosporins.