Long-term effect of epidural injection with sustained-release lidocaine particles in a rat model of postoperative pain.

Abstract

BACKGROUND:

Single applications of sustained-release local anaesthetics may provide prolonged pain relief without requiring indwelling catheters, but have not yet been investigated for epidural postoperative pain management. We synthesized injectable sustained-release lidocaine particles (SRLPs) from biodegradable polymers and examined their effect in a rat model of postoperative pain.

METHODS:

Two types of polylactic acid particles, SRLP-10 and SRLP-25, containing 10% or 25% lidocaine, respectively, were generated and the lidocaine release was evaluated in vitro for 14 days. The SRLPs were then injected epidurally in the male Sprague-Dawley rats immediately before they received a hindpaw incision (the postoperative pain model), and hindpaw hypersensitivity was evaluated with the von Frey test. Motor paralysis and coordination were also assessed using a paralysis score and rota-rod test. Neurotoxicity and inflammation of the spinal cord, cauda equina, and tissue surrounding the injection site were histologically evaluated.

RESULTS:

In vitro, SRLP-10 and SRLP-25 released lidocaine over 7 and 3 days, respectively. The in vivo injection of SRLP-10 (80 mg) produced anti-hypersensitivity with no evidence of motor paralysis for 7 days after the paw incision, and SRLP-25 (60 mg) inhibited postoperative hypersensitivity for 7 days. Temporary motor paralysis (15 min) was observed after the injection of SRLP-25 (even with 40 mg). Foreign body reactions were observed around the SRLP injection site at 1 and 4 weeks after injection. No histopathological changes were observed at 1 or 4 weeks.

CONCLUSIONS:

The epidural injection of SRLPs produced prolonged anti-hypersensitivity in a rat model of postoperative pain with no major complications.

• Authors: T Suto, H Obata, M Tobe, H Oku, H Yokoo, Y Nakazato, S Saito
• Journal: British journal of anaesthesia (Br J Anaesth) Vol. 109 Issue 6 Pg. 957-67 (Dec 2012) ISSN: 1471-6771 [Electronic] England
• PMID: 22923636 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Anesthetics, Local
• Delayed-Action Preparations
• Lidocaine

Topics

• Analysis of Variance
• Anesthetics, Local (pharmacology)
• Animals
• Delayed-Action Preparations
• Disease Models, Animal
• Dose-Response Relationship, Drug
• Injections, Epidural
• Lidocaine (pharmacology)
• Male
• Pain Measurement (methods)
• Pain, Postoperative (drug therapy)
• Rats
• Rats, Sprague-Dawley
• Time