Sl. Hao et al., Antinociceptive interaction between spinal clonidine and lidocaine in the rat formalin test: An isobolographic analysis, ANESTH ANAL, 92(3), 2001, pp. 733-738
Citations number
25
Categorie Soggetti
Aneshtesia & Intensive Care","Medical Research Diagnosis & Treatment
Clinical and basic science studies suggest that spinal alpha -2-adrenergic
receptor agonists and local anesthetics produce analgesia, but interaction
between alpha -2-adrenergic receptor agonists and local anesthetics in the
persistent pain model has not been examined. In the present study, using is
obolographic analysis, we investigated the antinociceptive interaction of i
ntrathecal clonidine and lidocaine in the rat formalin test. Sprague-Dawley
rats were implanted with chronic lumbar intrathecal catheters, and were te
sted for paw flinch by formalin injection. Biphasic painful behavior was co
unted. Intrathecal clonidine (3-12 nmol) was administered 15 min before for
malin, and intrathecal lidocaine (375-1850 nmol) was administered 5 min bef
ore formalin. To examine the interaction of intrathecal clonidine and lidoc
aine, an isobolographic design was used. Spinal administration of clonidine
produced dose-dependent suppression of the biphasic responses in the forma
lin test. Spinal lidocaine resulted in dose-dependent transient motor dysfu
nction and the motor dysfunction recovered to normal at 10-15 min after adm
inistration. Spinal lidocaine produced dose-dependent suppression of phase-
2 activity in the formalin test. Isobolographic analysis showed that the co
mbination of intrathecal clonidine and lidocaine synergistically reduced Ph
ase-2 activity. We conclude that intrathecal clonidine synergistically inte
racts with lidocaine in reducing the nociceptive response in the formalin t
est.