Long-term effect of ropivacaine nanoparticles for sciatic nerve block on postoperative pain in rats.
OBJECTIVE
The analgesic effect of ropivacaine (Rop) for nerve block lasts only ~3-6 hours for single use. The aim of this study was to develop long-acting regional anesthetic Rop nanoparticles and investigate the effects of sciatic nerve block on postoperative pain in rats.


METHODS
Rop nanoparticles were developed using polyethylene glycol-co-polylactic acid (PELA). One hundred and twenty adult male Wistar rats were randomly divided into four groups (n=30, each): Con (control group; 0.9% saline, 200 µL), PELA (PELA group; 10 mg), Rop (Rop group; 0.5%, 200 µL), and Rop-PELA (Rop-PELA group; 10%, 10 mg). Another 12 rats were used for the detection of Rop concentration in plasma. The mechanical withdrawal threshold and thermal withdrawal latency were measured at 2 hours, 4 hours, 8 hours, 1 day, 2 days, 3 days, 5 days, and 7 days after incision. The expression of c-FOS was determined by immunohistochemistry at 2 hours, 8 hours, 48 hours, and 7 days. Nerve and organ toxicities were also evaluated at 7 days.


RESULTS
The duration of Rop absorption in the plasma of the Rop-PELA group was longer (>8 hours) than that of the Rop group (4 hours). Mechanical withdrawal threshold and thermal withdrawal latency in the Rop-PELA group were higher than that in other groups (4 hours-3 days). c-FOS expression in the Rop-PELA group was lower than that in the control group at 2 hours, 8 hours, and 48 hours and lower than that in the Rop group at 8 hours and 48 hours after paw incision. Slight foreign body reactions were observed surrounding the sciatic nerve at 7 days. No obvious pathophysiological change was found in the major organs after Rop-PELA administration at 7 days.


CONCLUSIONS
Rop-PELA provides an effective analgesia for nerve block over 3 days after single administration, and the analgesic mechanism might be mediated by the regulation of spinal c-FOS expression. However, its potential long-term tissue toxicity needs to be further investigated.
Department of Anesthesiology, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Zi
Z
Wang
Department of Anesthesiology, Stomatology Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Haizhen
H
Huang
Department of Anesthesiology, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Shaozhong
S
Yang
Department of Anesthesiology, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Shanshan
S
Huang
Department of Anesthesiology, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Jingxuan
J
Guo
Department of Anesthesiology, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Qi
Q
Tang
Department of Anesthesiology, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China.
Feng
F
Qi
D000577:Amides / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000494:pharmacology; D000818:Animals; D007773:Lactates; D008297:Male; D053758:Nanoparticles / Q000008:administration & dosage* / Q000737:chemistry; D009407:Nerve Block / Q000379:methods*; D010149:Postoperative Pain / Q000188:drug therapy*; D011092:Polyethylene Glycols; D017208:Rats, Wistar; D000077212:Ropivacaine; D012584:Sciatic Nerve / Q000187:drug effects*; D013997:Time Factors
D000577:Amides; D000779:Anesthetics, Local; D007773:Lactates; C058523:polyethylene oxide-polylactic acid block copolymer; D011092:Polyethylene Glycols; D000077212:Ropivacaine
nanoparticle; polyethylene glycol-co-polylactic acid; postoperative pain; ropivacaine; sciatic nerve block