Pain is also a main cause of postoperative excitement. Dexmedetomidine, which is an S-enantiomer of medetomidine with high specificity for α2-adrenoceptor (α2 : α1, 1620 : 1) compared to clonidine (a2 : a1, 220 : 1), is approved as a sedative and co-analgesic drug.