Clonidine Versus Dexmedetomidine As Premedication to Intrathecal 0.5percent Levobupivacaine Heavy

Spinal anesthesia is a reliable and safe technique in lower limb and lower abdominal surgeries.[1] It is favorable when general anesthesia is contraindicated or in patients in whom anatomical abnormalities may make tracheal intubation very difficult.[2] Many techniques and drug regimens, with partial or greater success, have been tried from time to time to alleviate anxiety and prolong postoperative analgesia during regional anesthesia. Several adjuvants such as midazolam, opioids, and α2-adrenoceptor agonists have been studied in this regard. When used as adjuvant to regional anesthesia, alpha-2-adrenoceptor agonists have both analgesic and soothing properties.[ Clonidine and dexmedetomidine are the two most used drugs. Oral, spinal, and epidural are the various routes of administration of these drugs to prolong the duration of spinal anesthesia.[5-7] They prolong the duration of both motor and sensory blockade and also postoperative analgesia by potentiating the effect of local anesthesia Both spinal and supraspinal mechanisms have been proposed to explain their action. In the spinal cord, stimulation of α-adrenoreceptors at the substantia gelatinosa of the dorsal horn of the spinal cord leads to inhibition of nociceptive neurons. Stimulation of the adrenoreceptors in the locus coeruleus results in sedation and anxiolysis and also terminates propagation of pain signals leading to analgesia.[10] Clonidine is a selective partial agonist for alpha-2- adrenoreceptors used intrathecally, with a well-established record of efficacy and safety.[11] Dexmedetomidine is a highly selective alpha-2-adrenoreceptor agonist with the alpha-2: alpha-1 binding ratio of 1620: 1 when compared with 220:1 for clonidine which is 8–10 times higher than that of clonidine.[12] The prolongation of spinal anesthesia after intravenous (IV) administration of dexmedetomidine and clonidine can be explained by the supraspinal effects of these drugs.[13,14] There are limited studies to show the dose equivalence of these two drugs; however, some studies showed that the dose of clonidine is 1.5–2 times higher than the dose of dexmedetomidine.[15,16] Therefore, we designed this prospective, randomized,  study to compare the efficacy of the IV infusion of clonidine 0.75  µg/kg vs. dexmedetomidine 0.75 Âµg/kg on spinal block characteristics as premedication to intrathecal 0.5% hyperbaric levobupivacaine in patients undergoing various lower limb and lower abdominal surgeries.