The use of alpha-2 agonists in peripheral nerve blocks: a review of the history of clonidine and a look at a possible future for dexmedetomidine

Many additives to local anesthetics to prolong the duration of peripheral nerve blocks have been investigated throughout the years. Clonidine, an alpha-2 agonist, has shown efficacy with all local anesthetics in a variety of peripheral nerve block techniques. In vitro and in vivo laboratory animal studies indicate a direct action on the peripheral nerve by clonidine, which is not mediated via the alpha-2 receptor. Dexmedetomidine (Precedex^®) is a newer alpha-2 agonist that has shown some promise in a limited number of regional anesthesia investigations. The following article reviews the available clinical peripheral nerve block studies using clonidine, laboratory animal in vitro and in vivo studies on the effect of perineural clonidine, and studies using dexmedetomidine in regional anesthesia.