RESUMO
The effect of ropivacaine as a recent amino-amide local anaesthetic compared with bupivacaine on analgesic activities, cardiac contractility, blood pressure, heart rate, Electrocardiogram [ECG] and toxicity was studied. The result of our study revealed that ropivacaine Exhibited a less degree of analgesic potency than bupivacain, it increase the reaction time by 20.6 and up to 167.6% while bupivacaine increased it by 37.32 up to 197.1%. On isolated rabbits heart, ropivacaine and bupivacaine induced a significant dose dependent -ve inotropic effect. The cardiodepressant action of ropivacaine was lesser than that of bupivacaine. IV injection of ropivacaine [0.35-2.8mg/kg] produced slight increase in arterial blood pressure but in the last dose produce decrease in arterial blood pressure. Bupivacaine 0.5-1mg/kg produce no significant change in arterial blood pressure but in the subsequent doses it produces hypotension up to death, this hypotension may be the beginning effect of high toxic blood level of the drug. Ropivacaine showed no alterations in ECG apart from significant decrease in heart rate only in high doses, but on the other hand bradycardia started earlier with bupivacaine [1mg/kg] and ECG changes were seen after 5 minutes from injecting 2mg/kg which ended by cardiac arrest. In respect to toxicity, intra peritoneal LD50 of ropivacaine was found to be 115mg/kg compared to 90mg/kg of bupivacaine. We concluded that ropivacaine nearly resembles bupivacaine in its local analgesic effect but has a great margin of safety with less cardiodepressant action