In vitro activity: Dexmedetomidine has a relatively high ratio of α2/α1-activity (1620:1 as compared with 220:1 for clonidine) and, therefore, is considered a full agonist of the α2 receptor. This may result in more potent effects of sedation without unwanted cardiovascular effects from α1 receptor activation. The 2-h half-life of dexmedetomidine is nearly 4-fold shorter than that of clonidine, which increases the likelihood that a continuous infusion of dexmedetomidine might be useful for sedation. Dexmedetomidine also has minimum alveolar anesthetic concentration (MAC)-sparing properties, but its use as an anesthetic adjuvant has been complicated by persistent hypotension that has mandated IV fluid administration and vasopressor administration. In addition, its use in large doses is complicated by hypertension from α2 receptor-mediated vascular constriction.

Eur J Pharmacol. 1988 May 20;150(1-2):9-14; Anesthesiology. 1997 Feb;86(2):331-45.