This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
[{'content': 'A person has headache & profuse sweating. On examination his B.P is 200/120 mm Hg. Which of the following shoud not be used \nSelect and explain. \nA. Nifedipine, B. Sodium nitroprusside, C. Phenoxybenozamine, D. Methyldopa', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Patients who respond to shoacting vasodilators at the time of cardiac catheterization (a fall in mean pulmonary aerial pressure >=10 mmHg and a final mean pressure <40 mmHg) should be treated with calcium channel blockers. Typically, these patients require high doses (e.g., nifedipine, 240 mg/d, or amlodipine, 20 mg/d). Patients may have dramatic reductions in pulmonary aery pressure and pulmonary vascular resistance associated with improved symptoms, regressionof RV hyperophy, and improved survival now documented to exceed 20 years. However, <20% of patients respond to calcium channel blockers in the long term. These drugs are not effective in patients who are not vasoreactive. ref:Harrison&;s principles of internal medicine,ed 18,pg no 2079', 'role': 'assistant'}]