Sun21November0437PM 1

True / False

Can cause dose-dependent side effects such as hypertension and tachycardia Correct

Can be used caudally Incorrect answer selected

Is a selective alpha2-receptor agonist Correct

Is a stereoisomer Correct

Has a 100-fold affinity to the alpha2-receptor compared to clonidine Incorrect answer selected

Explanation

Dexmedetomidine is a selective alpha2-receptor agonist.1 It is the active stereoisomer of medetomidine; medetomidine is a racemic mixture but only the D-stereoisomer is active, so it has been developed as dexmedetomidine.2

Its mechanism of action is similar to clonidine although it is more potent and has a higher affinity for the alpha2-receptor. Dexmedetomidine has an eightfold affinity to the alpha2-adrenoreceptor.1

Dexmedetomidine has activity at a variety of locations throughout the central nervous system. These include the lateral reticular nucleus, locus ceruleus and spinal cord.

Stimulation of the lateral reticular nucleus and locus ceruleus results in reduced central sympathetic output and subsequent sedation and anxiolytic effects. Effects at the dorsal horn of the spinal cord augment endogenous opiate release modulating the descending noradrenergic pathways involved in spinal nociceptive processing.

Dexmedetomidine can be administered via intravenous infusion, intramuscularly, transdermally, intrathecally, epidural route and in combination with local anaesthetics in peripheral nerve blocks.3,4,5

The dose-dependent side effects are hypotension and bradycardia.6

Reference:

Marhofer D, et al. Dexmedetomidine as an adjuvant to ropivacaine prolongs peripheral nerve block: a volunteer study. Br J Anaesth. 2012;110:438-42.

Peck TE, Hill SA, Williams M. Pharmacology for Anesthesia and Intensive Care. 3rd ed. London: Cambridge University Press; 2008. p 267-268.

El-Hennawy AM, et al. Addition of Clonidine or Dexmedetomidine to Bupivacaine prolongs Caudal Analgesia in Children. Br J Anaesth. 2009;103:699-705.

Kivistö KT, et al. Pharmokinetics and Pharmacodynamics of Transdermal Dexmedetomidine. Eur J Clin Pharmacol. 1994;46:345-9.

Bajwa SJ et al. Dexmedetomidine and Clonidine in Epidural Anaesthesia: A comparative evaluation. Indian J Anaesth. 2011;55:116-121.

Saadawy, et al. Effects of Dexmedetomidine on the Characteristics of Bupivacaine in a Caudal Block in Paediatrics. Acta Anaesthsiol Scand. 2009;53:251-256.

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Times answered: 254