Primary evaluation of the local anaesthetic properties of the amino amide agent ropivacaine (LEA 103).

The local anaesthestic properties of 1-propyl-2',6'-pipecoloxylidide, a congener of mepivacaine and bupivacaine, and its enantiomers were compared in animals. The (S)-enantiomer (ropivacaine, LEA 103) produced a longer duration of sciatic nerve block and infiltration anaesthesia than the racemate and the (R)-form. Ropivacaine and bupivacaine were equally potent in terms of block of evoked action potential in vitro and minimum effective concentration in vivo. Ropivacaine 0.25-1.0% was distinctly longer acting than bupivacaine on infiltration, equally effective in sciatic and brachial plexus block and somewhat shorter lasting in epidural and spinal blockade. There were tendencies towards a greater benefit from the addition of adrenaline with ropivacaine in epidural anaesthesia and a shorter latency to block in some of the tests. Ropivacaine seems less vasodilative than bupivacaine and capable of producing some vasoconstriction over a wider range of low concentrations, which may explain its longer duration of intradermal anaesthesia. The somewhat shorter duration of central blockade of ropivacaine is probably a result of lesser lipid solubility. Ropivacaine was less toxic (i.v. and s.c. LD50-values) than bupivacaine but more toxic than lidocaine, and produced only weak local irritation. Due to a combination of interesting local anaesthetic properties and relative safety including cardiotoxic potential, we consider ropivacaine a candidate for further studies.