New amide local anaesthetics for obstetric use.

For a number of reasons, bupivacaine has become the most frequently used local anaesthetic in obstetric anaesthesia, despite the fact that it has a narrower margin of safety than other local anaesthetics. In recent years, advances in technology have made single-isomer formulations of drugs available for clinical use. Generally speaking, the levo stereoisomer of amide local anaesthetic has a lower potential for systemic toxicity than the dextro form of the drug while retaining anaesthetic potency. Ropivacaine (Naropin, Astra Ltd), a homologue of mepivacaine and bupivacaine, has recently been released for use. Its clinical efficacy appears to be quite similar to that of bupivacaine but it has a greater margin of safety. The other drug currently being investigated is levobupivacaine (Chirocaine, Chiroscience Ltd). Both drugs appear to be similar in efficacy to the currently used formulation of bupivacaine; however, they are more costly. Thus, cost-benefit analyses are required to define more clearly their future role in obstetric anaesthesia.