Long-term effect of sciatic nerve block with slow-release lidocaine in a rat model of postoperative pain.
BACKGROUND
Postoperative pain management is important for preventing perioperative complications. The authors examined the effectiveness of controlled-release lidocaine for sciatic nerve block in a rat model of postoperative pain.


METHODS
The authors created a novel slow-release lidocaine sheet (SRLS) with polylactic-coglycolic acid. In male Sprague-Dawley rats (postoperative pain model), the authors applied the SRLS, lidocaine alone, or polylactic-coglycolic acid (control) near the ipsilateral sciatic nerve just before making the paw incision. Mechanical hypersensitivity was assessed using von Frey filaments, and c-fos expression was examined in the spinal cord dorsal horn at segments L4-L5. Neurotoxicity and muscle toxicity were also evaluated via histopathology.


RESULTS
The SRLS (30%, w/w) continuously released lidocaine for 1 week in vitro. The withdrawal threshold in the SRLS-treated group was higher than that in the control group at all time points measured (2 h to 7 days). The withdrawal threshold in the lidocaine-treated group was higher than that in the control group only at 2 h after paw incision. The mean number of c-fos immunoreactive neurons in the SRLS-treated group was lower than in the control group at 2, 5, and 48 h after paw incision and lower than in the lidocaine-treated group at 5 and 48 h after paw incision. On histopathology, signs of inflammation were only slightly present in the muscle and nerve tissues of the SRLS-treated group.


CONCLUSIONS
Single treatment with the SRLS inhibited hyperalgesia and c-fos expression in the spinal cord dorsal horn for 1 week. Slow-release local anesthetics are promising for the management of postoperative pain.
Tobe
Masaru
M
Department of Anesthesiology, Gunma University Graduate School of Medicine, Maebashi, Japan.
Obata
Hideaki
H
Suto
Takashi
T
Yokoo
Hideaki
H
Nakazato
Yoichi
Y
Tabata
Yasuhiko
Y
Saito
Shigeru
S
D000818:Animals; D003692:Delayed-Action Preparations / Q000008:administration & dosage / Q000493:pharmacokinetics; D004195:Disease Models, Animal; D016503:Drug Delivery Systems / Q000379:methods*; D008012:Lidocaine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D009407:Nerve Block / Q000379:methods*; D010149:Postoperative Pain / Q000188:drug therapy* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
D003692:Delayed-Action Preparations; D008012:Lidocaine