Effects of CNS site-directed carotid arterial infusions of bupivacaine, levobupivacaine, and ropivacaine in sheep.

Background: Previous preclinical safety studies in ewes have found intravenous levobupivacaine and ropivacaine to be less potent toward causing central nervous system (CNS) and cardiac toxicity than bupivacaine. Analogous cardiotoxicity has been demonstrated directly in various cardiac preparations ex vivo. Moreover, drug-related arrhythmogenicity has been demonstrated from direct CNS injection of local anesthetic agents in vivo, suggesting CNS-related cardiotoxicity. This study investigated whether CNS site-directed blood-borne drug administration (with minimal systemic recirculation) would demonstrate drug-related cardiotoxicity.

Methods: Direct CNS effects and indirect cardiotoxic sequelae were determined after bilateral carotid arterial infusions of levobupivacaine, bupivacaine, or ropivacaine in ewes. After pilot studies to validate the procedures, equimolar doses (24-96 micromol, approximately 7.5-30 mg) were infused over 3 min using a crossover design. Behavioral CNS signs, quantitative electroencephalographic (EEG), cardiovascular, and electrocardiographic effects were recorded. Drug blood concentrations in superior sagittal sinus and aorta were measured serially.

Results: Blood drug concentrations in the superior sagittal sinus were 5-10 times those concurrently in the aorta, confirming highly selective CNS delivery with minimal systemic recirculation. Dose-dependent CNS excitatory behavior and EEG changes, with increased mean arterial blood pressure, heart rate, cardiac output, and myocardial contractility, were found, consistent with sympathetic nervous system stimulation. The overall rank order of potency for these effects was ropivacaine < levobupivacaine < bupivacaine. Nonfatal cardiac arrhythmias were observed, but the type or frequency did not differ between drugs.

Conclusions: Although CNS site-selective drug delivery produced quantitative differences between bupivacaine, levobupivacaine, and ropivacaine in some CNS effects and cardiac sequelae, no differences were found in their arrhythmogenic potential.