Comparison of the effects of intrathecal administration of levobupivacaine and lidocaine on the prostaglandin E^sub 2^ and glutamate increases in cerebrospinal fluid: a microdialysis study in freely moving rats

BACKGROUND: Bupivacaine has a lower incidence of transient neurological symptoms than lidocaine after intrathecal (i.t.) injection. The increased toxic potential of lidocaine does not support its use in the clinical setting and could be related to augmented levels of spinal prostaglandin E(2) (PGE(2)). We tested whether levobupivacaine leads to lower PGE(2) levels than lidocaine. Moreover, we compared the release of PGE(2) and glutamate after i.t. injections of levobupivacaine or lidocaine. METHODS: Rats were anaesthetized for implantation of an i.t. dialysis catheter. This allowed sampling dialysates of cerebrospinal fluid (CSF) for measuring PGE(2) and glutamate levels. The microdialysis setting included baseline sampling and was followed by an i.t. injection of levobupivacaine 250 microg, 100 microg, or saline. PGE(2) and glutamate levels in CSF were analysed for 4 h. In addition, the residual effect of a second i.t. injection on, respectively, of PGE(2) and glutamate changes was compared after injection of either 250 or 100 microg levobupivacaine, 1000 or 400 microg lidocaine, or saline. RESULTS: Prolonged spinal PGE(2) increases lasting 50-120 min were observed after levobupivacaine injection. Higher PGE(2) concentrations were observed after the second lidocaine 1000 microg injection. Glutamate release after the second injection did not vary between the local anaesthetic groups. CONCLUSIONS: Spinal PGE(2) levels are similarly increased after i.t. levobupivacaine injection of 250 and 100 microg. A higher PGE(2) response was observed after a second i.t. injection in the animals receiving 1000 microg lidocaine than those receiving 400 mg lidocaine or either dose of levobupivacaine.