Although
local anesthetics can, in some situations, alleviate
neuropathic pain, currently available preparations are short-acting and nonselective, producing, for example, motor dysfunction. Clinical studies report that a novel
suspension preparation of
butamben has the advantage of a prolonged duration of action, and it can be used epidurally, without impairment of motor function. In this behavioral study, we investigated the effect of the epidural administration of a 5%
butamben suspension on nerve injury-induced
allodynia. Behavioral studies were performed using an established animal model of
neuropathic pain, which involves a partial
ligation of the sciatic nerve. Nociceptive thresholds to mechanical stimulation were determined by the paw withdrawal method. The
allodynia to mechanical stimulation induced by partial nerve
ligation was significantly attenuated by daily
injections, for 5 days, of 10 microL of
butamben suspension. The
analgesia lasted at least 7 days after the final injection. Daily
injections of 10 microL of vehicle, for 5 days, had no significant effect on
allodynia. During the period of daily
injections, both the
butamben and vehicle treated rats had temporary impairment of motor coordination compared with untreated controls. Motor function recovered after the final injection. Neither daily
injections of
butamben for 2 or 3 days, nor smaller volumes for 5 days (2.5-5 microL), had a long-lasting effect. We conclude that repeated epidural administration of
butamben suspension for several days provides long-lasting
analgesia in rats with nerve injury-induced
allodynia to mechanical stimulation.
IMPLICATIONS: In this animal behavioral study, using rats with nerve injury-induced
pain, we examined the possible long-term
analgesic effects of epidural administration of a
suspension of the
local anesthetic,
butamben. We found that multiple doses for several days were required to provide a prolonged
analgesia.