This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'All of the following are true regarding penicillin except: March 2005 \nSelect and explain. \nA. Probenecid decreases it duration of action, B. All penicillin are active against gram positive organisms, C. Splits into 6-amino penicillanic acid by amidase, D. Acts by inhibiting cell wall synthesis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A: Probenecid decreases it duration of action Drug interactions have been deliberately used to prolong the effect of penicillin, such as co-administering probenecid with penicillin prior to mass production of penicillin. Because penicillin was difficult to manufacture, it was wohwhile to find a way to reduce the amount required. Probenecid retards the excretion of penicillin, so a dose of penicillin persists longer when taken with it and it allowed patients to take less penicillin over a course of therapy.', 'role': 'assistant'}]