This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sympathetic System, Subject name: Pharmacology
[{'content': 'The drug that causes first dose phenomenon in elderly patients - \nSelect and explain. \nA. Metformin, B. Prazosin, C. Acarbose, D. Noradrenaline', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The side effect postural hypotension also known as "First Dose Hypotension" is observed with drugs ending with \'zosin\' eg. Prazosin, Terazosin,Doxazosin These drugs cause blocking of a1 receptors, leading to vasodilation, that can cause Postural Hypotension. Acarbose - Inhibition of intestinal absorption of carbohydrates. S/E - flatulence, abdominal discomfo, loose stool. Metformin - S/E - Abdominal Pain, Anorexia, bloating, nausea, metallic taste mild diarrhea & tiredness. Noradrenaline (Pressor agent)- stimulates a1 and a2 receptors, thus increases peripheral vascular resistance and result in increase BP. It acts on b1 adrenergic receptors, causing increase In hea rate and cardiac output. S/E = Transient restlessness, headache, palpitations, Anxiety, tremor.', 'role': 'assistant'}]