BACKGROUND:Clonidine is an α2 adrenoreceptor agonist that has been shown to effectively prolong the duration of analgesia when administered intrathecally or in the epidural space along with local anaesthetic. AIMS AND OBJECTIVE: This study was designed to evaluate the effect of two different doses of intrathecal clonidine (37.5 µg and 75 µg) on the duration of analgesia and side effects produced by hyperbaric bupivacaine 0.5%. MATERIALS AND METHODS: A prospective hospital based, randomized and double blind study. Selected 75 patients who was scheduled for elective below umbilical surgeries were randomly allocated to one of three groups. Group I (n=25, control group) received 3ml hyperbaric bupivacaine, Group II (n=25) 3ml hyperbaric bupivacaine + 37.5 µg clonidine and Group III (n=25) 3 ml hyperbaric bupivacaine + 75μg clonidine intrathecally. Total volume (4ml) remained constant by adding sterile water. Data were analyzed by using SPSS software ver.18. RESULTS: The (mean ±SD) duration of analgesia was found to be 171.3±6.37 mins in Group I, 217.7±7.01 mins in Group II and 257.1±6.50 mins in Group III (p<0.05). It shows that 37.5g & 75g intrathecal clonidine increases the duration of analgesia of 15mg hyperbaric bupivacaine by about 46 mins & 86 mins respectively. The addition of intrathecal clonidine upto 75 µg does not cause any significant major side effect except mild sedation, without an increase in incidence of hypotension, bradycardia and respiratory depression. CONCLUSION: Intrathecal clonidine (37.5g & 75g) as an adjuvant to hyperbaric bupivacaine 0.5% prolong the duration of analgesia in a dose dependent manner without increase in incidence of significant side effects. KEYWORDS: hyperbaric bupivacaine, intrathecal clonidine, spinal anaesthesia. INTRODUCTION:Spinal anaesthesia is a well-established technique. It is easy to perform, to provide fast onset and effective sensory and motor block. Now a days bupivacaine is a commonly used local anaesthetic drug in spinal anaesthesia. However duration of spinal analgesia by bupivacaine is limited upto 75-150 min. Therefore various additives like clonidine, opioids, neostigmine, ketamine and epinephrine separate or in combination were used along with bupivacaine for prolongation of the effect, to improve the quality of analgesia and to minimize the requirement for postoperative analgesics.Clonidine is an α2 adrenoreceptor agonist that has been shown to effectively prolong the duration of analgesia when administered intrathecally or in the epidural space. (1,2,3) The α2 adrenergic agonist clonidine has a variety of different actions including the ability to potentiate the effects of local anaesthetics. Such prolongation of the effects of local anesthetics has been reported with oral. (4) IV (5) and intrathecal clonidine. (6,7) However, unlike spinal opioids, clonidine does not produce pruritus, urinary retention, respiratory depression, vomiting with no or minimum CNS depression. However, intrathecal clonidine at high doses is associated with brady...