Co-injection of clonidine prolongs the anesthetic effect of lidocaine skin infiltration by a peripheral action.

Background: The addition of clonidine to local anesthesia prolongs the local anesthetic action, but in humans, the contribution of a peripheral mechanism remains unclear.

Methods: We investigated clonidine's peripheral effect in 20 healthy volunteers undergoing double-blind, subcutaneous infiltration of 0.5% lidocaine with normal saline to one forearm and then, immediately, of lidocaine with 10 mug clonidine to the contralateral arm. Pinprick sensation was tested every 15 min for 6 h.

Results: Median time to return of normal sensation was 3.5 h for lidocaine alone, but at least 6 h if combined with clonidine (P < 0.001).

Conclusions: Clonidine has a significant peripheral action in enhancing duration of local anesthesia on superficial co-infiltration with lidocaine.