This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pharmacodynamics, Subject name: Pharmacology
Which of the following act on a-2 receptors - 
Select and explain. 
A. Rhenylephrine, B. Mitodrine, C. Clonidine, D. Methoxomine
C: Clonidine
Answer: C: Clonidine 
Explanation: Ans. is 'c' i.e., Clonidinea-2 agonistso These are:a) Apraclonidine and brimonidine are used in glaucoma.b) Dexmedetomidine is used as preanaesthetic medication and for sedation in critically ill/ventilated patient in ICU.c) Tizanidine is used as muscle relaxant in spaciticity.d) Clonidine and a methyldopa are used in hypertension. Other uses of clonidine are (i) preanaesthetic medication, (ii) diarrhea in diabetic neuropathy, (iii) analgesic, (iv) withdrawal syndrome of opoid, alcohol and nicotine, (v) prophylaxis of migrain, (vi) postmenopausal syndrome, (vii) suppression test for pheochromocytoma, and (viii) for treatment of ADHD.