Abstract:

Objective  To investigate the efficiency of ropivacaine PEG-PLA microspheres for sciatic nerve block in rats. Methods  Eighty Wistar rats were randomly divided into four groups (n=20, each) and were treated with 0.2mL of 0.9% saline(control group),10mg of PEG-PLA(PEG-PLA group), 0.2mL of 0.5% ropivacaine(ropivacaine group) and 10mg of 10% Rop-PEG-PLA microspheres(Rop-PEG-PLA group), respectively. The incision pain models were produced as described by Brennan. Mechanical thresholds and thermal latencies were measured at 24h before incision and at 2, 4, 8h, as well as 1, 2, 3, 5 and 7d after incision. Expression of c-fos protein in the spinal cord was determined by immunohistochemistry at 2h and 2d after incision. The ropivacaine concentration in plasma of ropivacaine group and Rop-PEG-PLA group was detected by HPLC analysis. Results  Behavioral testing and c-fos expression in PEG-PLA group showed no significant difference compared with those in control group(P＞0.05). The thresholds and latencies in ropivacaine group and Rop-PEG-PLA group were significantly higher than those in control group at 2h after incision(P＜0.05). Expressions of c-fos protein were suppressed in ropivacaine group and Rop-PEG-PLA  group at 2h after incision, compared with that in  control group(P＜0.05). The duration of anti-hyperalgesia effect（3d vs 2h）and ropivacaine concentration in plasma ( 8h vs 4h) in Rop-PEG-PLA group were longer than those  in ropivacaine group, and c-fos expression in Rop-PEG-PLA group was  lower than that in ropivacaine group at 2d after incision (P＜0.05). Conclusion  Single administration of ropivacaine PEG-PLA microspheres for sciatic nerve block provides effective analgesia for postoperative pain for 3d.

Key words: Microparticle, Ropivacaine, Sciatic nerve block, c-fos, Poly (ethylene glycol)-co-poly (D,L-lactic acid)