Sciatic Nerve Blockade in Infant, Adolescent, and Adult Rats: , A Comparison of Ropivacaine with Bupivacaine

Background: Ropivacaine is a newly introduced local anesthetic. anesthetic. No data are available regarding its safety, efficacy, or sensory-selectivity in children. The sciatic block duration and systemic toxicity of bupivacaine and ropivacaine were compared compared among infant, adolescent, and adult rats.

Methods: Infant, adolescent, and adult rats received blocks with ropivacaine or bupivacaine. Nociceptive, proprioceptive, and motor blockade were assessed. Systemic effects (contralateral leg analgesia, seizures, respiratory distress, apnea) were quantified. Plasma local anesthetic concentrations were measured at terminal apnea.

Results: Nerve blockade for a given absolute dose lasted longer in infants than in older rats for both drugs. Block duration duration from ropivacaine generally was the same as or slightly shorter than bupivacaine. There was no difference in sensory-selectivity between the drugs. Doses required to induce all systemic toxicity indices were inversely related to age (e.g., the lethal dose in 50% of animals [LD50] of ropivacaine in infants is 155 mg/kg; in adults it is 54 mg/kg). All indices of toxicity occurred at higher doses per kilogram for ropivacaine than bupivacaine, at all ages (e.g., the LD50 of bupivacaine in infants is 92 mg/kg; in adults it is 30 mg/kg). Plasma concentrations at terminal apnea were higher for ropivacaine than for bupivacaine at all ages, and were higher in infants than in older rats.