The enantiomerically pure (S-enantiomer) amide local anaesthetic drug ropivacaine blocked nerve fibres responsible for transmission of pain (A delta and C fibres) more completely than those that control motor function (A beta fibres) in in vitro studies. The drug shares the biphasic vascular effects common to the amide local anaesthetic drug class. In vitro studies indicate that ropivacaine is less cardiotoxic than equimolar concentrations of bupivacaine. Apart from one trial in women undergoing hysterectomy, clinical studies that compared the efficacy of different doses of epidurally administered ropivacaine in patients under going various surgical procedures did not reveal any consistent dose-related differences with respect to sensory blockade. However motor blockade did become more intense as the dose of ropivacaine increased Overall, direct comparisons show that epidural ropivacaine is less potent than epidural bupivacaine when the 2 drugs are administered at the same concentration. However, this difference is less marked in terms of sensory blockade than motor blockade. The greater degree of separation between motor and sensory blockade seen with ropivacaine relative to bupivacaine is more apparent at the lower end of the dosage scale. Nevertheless, higher doses of ropivacaine than bupivacaine are generally required to elicit equivalent anaesthetic effects. Ropivacaine has been shown to induce successful brachial plexus anaesthesia when given at a concentration of 5 mg/ml, but not 2.5 mg/ml, and was as effective as bupivacaine in comparative studies in this indication. Limited data indicate that continuous epidural infusion of ropivacaine postoperatively reduces postsurgical pain in a dose-related manner Morphine consumption was also reduced. Higher doses of ropivacaine were significantly more effective than placebo. Similarly ropivacaine controlled postsurgical pain when infiltrated directly into surgical wound sites (i.e. wound infiltration) and was as effective as bupivacaine, and more effective than placebo, in this regard. Adverse events associated with epidurally administered ropivacaine include hypotension, nausea, bradycardia, transient paraesthesia, back pain, urinary retention and fever. The drug appears to have an adverse event profile similar to that of bupivacaine. In animal studies, overdoses of ropivacaine were better tolerated than overdoses of bupivacaine but not lidocaine (lignocaine). Human volunteers tolerated a higher intravenous dosage of ropivacaine than bupivacaine before developing initial signs of toxicity Thus, ropivacaine, according to animal data, is less cardiotoxic than bupivacaine. Based on available clinical data, ropivacaine appears to be as effective and at ell tolerated as bupivacaine when equianalgesic doses are compared The greater degree of separation between motor and sensory blockade seen with ropivacaine relative to bupivacaine at lower concentrations (similar to 5 mg/ml) will be advantageous in certain applications.
