HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ASSAY OF MEPIVACAINE ENANTIOMERS IN HUMAN PLASMA IN THE NANOGRAM PER MILLILITER RANGE

A method enabling quantification of R-(-)- and S-(+)-mepivacaine in hu man plasma in the low nanogram per milliliter range is described. The procedure involves extraction from plasma with diethyl ether, centrifu gation, back-extraction into an acidified aqueous solution, washing wi th a mixture of pentane and isoamylalcohol, alkalinisation, followed b y extraction with a mixture of n-pentane and isoamylalcohol. After eva poration of the organic phase, the residue is redissolved in the mobil e phase used for the HPLC analysis, which consists of a 6.8:93.2 (v/v) isopropanol-sodium hydrogenphosphate buffer solution with the pH adju sted to 6.8 using phosphoric acid. The HPLC method has been described previously. Separation of the enantiomers is achieved with an alpha(1) -AGP column and the UV detection wavelength is 210 nm. The minimal det ectable concentration is ca. 3 ng/ml and the lower limit of quantifica tion is 5 ng/ml for each enantiomer. For both enantiomers r is >0.9995 over the plasma enantiomeric concentration range of 10.5-1053 ng/ml.