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: Anaesthesia
[{'content': 'Local anaesthetic with maximum ionized form at physiological pH – \nSelect and explain. \nA. Lignocaine, B. Etidocaine, C. Bupivacaine, D. Chloroprocaine', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Local anaesthetics with pKa value closest at physiological pH (7.4) will have a higher concentration of nonionized (unionized) base. Thus, the agent with pKa value away from physiological pH will have more concentration of ionized form.\nChloroprocaine has highest pKa value, hence maximum ionized form at physiological pH.\n\nLocal anaesthetics with pKa value in increasing order\nMepivacaine (7.6) < Etidocaine (7.7) < Lidocaine (7.8) = Prilocaine (7.8) < Bupivacaine (8.1) \n= Ropivacaine (8.1) < Tetracaine (8.2) < Cocaine (8.7) < Procaine (8.9) < Chloroprocaine (9.0)', 'role': 'assistant'}]