Biol. Pharm. Bull. 28(12) 2271—2273 (2005)

anesthetic agent as well as lidocaine, bupivacaine and mepivacaine (Fig. 1). Unlike bupivacaine and mepivacaine, which are racemic mixtures of the enantiomers containing equal proportion of the (S) and (R) forms, ropivacaine is exclusively the (S)-enantiomer. Since the (R)-enantiomer in the racemic aminoamide has known to be toxic, ropivacaine potentially provides lower toxicity on heart and central nervous system compared with bupivacaine and mepivacaine. Ropivacaine has an advantage over lidocaine in the drug metabolism. Lidocaine produces the toxic metabolites, monoethyl-glycinexylidide and glycinexylidide, in its hepatic metabolism, which are circulating with higher concentration in blood. On the other hand, blood concentrations of ropivacaine metabolites, 3-hydroxy-ropivacaine and 2-hydroxy-methyl-ropivacaine, have known to be very low (undetectable levels), even though they are pharmacologically active. These characteristics of ropivacaine may be suitable for the viscous preparation used for pain relief in oral cancer patients, because the patients sometimes swallow the viscous preparation accidentally. To assess the safety of ropivacaine viscous, we firstly need to determine the plasma ropivacaine concentration when applied to oral mucosa. The reported HPLC method for measuring plasma ropivacaine employed solid-phase extraction and C8 column, CN column or column switching technique for the separation. We developed a rapid and sensitive method for quantitating plasma ropivacaine by combined use of ODS column and liquid–liquid extraction with ethylacetate.