“A comparison of fentanyl and clonidine as adjuvants to intrathecal levobupivacaine for spinal anaesthesia and postoperative analgesia in patients undergoing for lower limb surgery”, Int Jour of Biomed Res, vol. 9, no. 2, pp. 76–80, Mar. 2018, doi: 10.7439/ijbr.v9i2.4622.