Materials and Methods

A modified gas-liquid chromatographic method for de-termining plasma concentrations of bupivacaine and lid-ocaine is described, with cyclizine as an internal standard. The extraction procedure requires no solvent evaporation, thus overcoming the problem of drug volatility. Concen-trations as low as 0.1 mg/liter can be determined. The plasma sample is made alkaline and extracted into n-hexane, re-extracted into a small volume of an aqueous acid phase, and finally extracted into 50 p1 of methylene chloride after alkallnization. The final extract is assayed by gas chromatography on a 5 % OV-17 column. The ex-traction scheme of the present method eliminates inter-ferences by endogenous plasma constituents. Bupivacaine (Marcaine) is a local anesthetic of the anilide type with an action longer than that of lidocaine (Xylocaine) and mepivacaine (Carbocaine) (1-3). Most of the systemic toxic reactions from the local anesthetics are correlated with high concentrations of these drugs in plasma, the peak values for bupivacaine or lidocaine after different regional anesthetic techniques ranging from 1.5 to 4.5 mg/liter. Signs of toxicity occur when the concentration in plasma exceeds 5 mg/liter (4). Determinations of these drugs in plasma can therefore make their use safer, and may help throw light on various phar-macokinetic processes occurring in patients. This information is of value to the clinician for the choice and the dosage of the drug to be used. Several gas-chromatographic methods for determination of bupivacaine (5-8) and lidocaine (9-12) have been reported. However, they involve various extraction procedures and the organic phase must be purified before the solvent is evapo-rated. These time-consuming procedures can lead to lower recovery and sensitivity due to adsorption of the drug to the glasswareand evaporation of volatile components. The method described herein allows more rapid measure-ment of bupivacaine and or lidocaine in plasma