Dexmedetomidine Increases the Latency of Thermal Antinociception in Rats

Recent reports have stated that dexmedetomidine (DEX), an α₂-adrenoreceptor agonist, enhances the local anesthetic effects of ropivacaine and prolongs its effective duration. However, little is known about the effect of a combination of DEX and lidocaine on anesthetic duration. Therefore, we investigated whether DEX can prolong the local anesthetic effect of lidocaine, using the thermal paw withdrawal test in Wistar rats in order to measure local anesthetic duration. We subcutaneously injected 50 μL of either normal saline, 2% lidocaine, a combination of 0.5 μg/kg DEX and 2% lidocaine, or a combination of 2% lidocaine with 1:80,000 epinephrine into the plantar surface of the left hind paw of the rats. The plantar region was stimulated using heat. We measured the perceived acute pain according to paw movement in response to stimulation. We found DEX significantly prolonged the paw withdrawal latency of lidocaine. Moreover, we found that DEX can prolong the local anesthetic duration of lidocaine as much as 1:80,000 epinephrine, up to 35 minutes after injection. In conclusion, this study concluded that a combination of DEX and lidocaine may be useful as a local anesthetic, similar to a combination of epinephrine and lidocaine, for short procedures.