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Abstract
Ropivacaine is a local anesthetic widely used for regional anesthesia and epidural analgesia, but its relatively short duration limits its clinical use. A novel sustained release lipid formulation of ropivacaine has been recently developed to prolong its duration. We examined the epidural anti-hypersensitivity and preemptive effects of ropivacaine in mesylate injection and sustained release suspension forms in a rat model of neuropathy produced by peripheral nerve injury. Epidural administration of ropivacaine mesylate injection specifically blocked mechanical allodynia and thermal hyperalgesia by approximately 50% with a biological half-effective duration of approximately 3 hrs. The equivalent dose of ropivacaine free-base in sustained release suspension significantly prolonged the duration of anti-allodynia and anti-hyperalgesia by approximately 2 times. Multiple daily epidural injections of ropivacaine in both the mesylate injection and sustained-release suspension forms did not induce tolerance or potentiation to anti-allodynia or anti-hyperalgesia. Moreover, the single or multiple daily administration of ropivacaine mesylate injection before surgery in particular, markedly blocked the initiation and development of neuropathic pain, increasing the biological half-effective duration from less than 4 hrs up to 1 or 2 days. The single and multiple daily epidural injection of ropivacaine sustained release suspension further delayed the biological half-lives to 2 and 3 days, respectively. Our results indicate that the epidural administration of ropivacaine effectively blocks neuropathic pain without the induction of analgesic tolerance, and significantly delays the development of neuropathy produced by peripheral nerve injury. Epidural ropivacaine sustained release suspension produces much longer blockade effects of mechanical allodynia and heat hyperalgesia, and more significantly delays the development of neuropathic pain.
Highlights
Local anesthetics, administered via the peripheral or central route, are widely used for regional anesthesia and control of postoperative pain and chronic pain, including neuropathic pain [1]
Our results indicate that epidural administration of ropivacaine effectively blocks neuropathic pain without induction of analgesic tolerance and significantly delays the development of neuropathic pain produced by peripheral nerve injury
To determine the doses and observation period for ropivacaine to produce antinociception, we first examined the motor blockade effect of epidural administration of ropivacaine both in mesylate injection form and sustained release suspension form in eight groups of rats (n = 6 in each group and no animals were excluded from the study)
Summary
Local anesthetics, administered via the peripheral or central route, are widely used for regional anesthesia and control of postoperative pain and chronic pain, including neuropathic pain [1]. Ropivacaine, which is chemically homologous to bupivacaine and mepivacaine, belongs to the class of long-acting amide-type local anesthetics [2]. It shows better sensory-motor differential blockade, less central nervous system and cardiovascular toxicities or side-effects, and longer duration than bupivacaine and other agents in the class [3,4,5,6]. Epidural ropivacaine at concentrations of 0.2–1% has been increasingly used in clinical practice to provide regional anesthesia and postoperative pain relief [5, 6]. Wide clinical use of ropivacaine has prompted the development of appropriate delivery systems and different administration regimens that circumvent the problem of rapid clearance from the injection site into systemic circulation [9]
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