This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cell Wall Synthesis Inhibitors, Subject name: Pharmacology
The penicillin G preparation with the longest duration 
Select and explain. 
A. Benzathine penicillin, B. Sodium penicillin, C. Potassium penicillin, D. Procaine penicillin
A: Benzathine penicillin
Answer: A: Benzathine penicillin 
Explanation: Penicillin G due to it's rapid tubular secretion, it is very sho acting. It's duration of action is increased with probenecid which compete with penicillin at tubular pump. Procaine penicillin G and benzathine penicillin G are administered IM and serve as depot forms. They are slowly absorbed into the circulation and persist at low levels over a long time period. Specially Benzathine penicillin G has longest duration of action. Penicillin G are not effective orally as it is acid labile. Penicillin which are acid stable are : - V : Penicillin V- O: Ofloxacillin- D: Dicloxacillin- K: Cloxacillin- A: Amoxicilin/Ampicillin