This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
[{'content': 'Insulin of choice for the treatment of diabetes mellitus is: \nSelect and explain. \nA. Regular Insulin, B. NPH insulin, C. Insulin glargine, D. Insulin lispro', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (Ref: Katzung 14th ed. P 753)Regular insulin is a short-acting, soluble crystalline zinc insulinHypoglycemic effect appears within 30 minutes after subcutaneous injection, peaks at about 2 hours, and lasts for 5-7 hours.For very insulin-resistant subjects who would otherwise require large volumes of insulin solution, a U500 preparation of human regular insulin is available both in a vial form and a disposable penIV infusion: used in treatment of diabetic ketoacidosis', 'role': 'assistant'}]