The present study was designed to test whether
tramadol is effective in the control of
neuropathic pain in rats. Chronic constriction injury (CCI) of the sciatic nerve was induced over the left hind limb in male Sprague-Dawley rats. Identical surgery was performed on the opposite side except that the sciatic nerve was not ligated (
sham surgery). Paw withdrawal latency (PWL) to heat was tested for each hind paw 1 day before surgery and on the 4th day after surgery to ensure the development of
thermal hyperalgesia. In the acute treatment groups, saline or
tramadol was administered subcutaneously at doses of 10, 20 or 30 mg/kg, and PWLs were measured 30, 60, 90, 120, 150 and 180 min
after treatment. In the semi-chronic treatment groups, continuous systemic administration of
tramadol 40 mg/kg/day or saline for 7 days was provided at a uniform rate via osmotic mini pumps.
Tramadol reversed PWL in a dose-dependent manner in the acute treatment groups. PWLs were significantly reversed at 2 days after
tramadol infusion, and this effect was sustained throughout the remainder of the treatment period in comparison with the saline group.
Tramadol also resulted in a decreased sensitivity to thermal stimulus on the
sham limb both in acute and semi-chronic administration. We conclude that both acute and semi-chronic
tramadol treatment relieves
thermal hyperalgesia effectively in rats with CCI of the sciatic nerve. This indicates that
tramadol shows promise as a potential treatment for relief of
neuropathic pain in humans.