Abstract: AIM:To develop an assay for the quanti- fication of the loxoprofen in human plasma and study its pharmacokinetics and bioequivalence in healthy volun- teers .METHODS:The method involves the addition of ibuprofen ( internal standard) solution in methanol, hex- ane-ether ( 4 ∶1, v/v ) solution to 0 .2 ml acidified plas- ma sample, followed by centrifugation .Separations were performed on Diamonsil 150 mm ×2 .1 mm, 5 μm column with the mobile phase of 0 .2 %NH4 Ac-acetonitrile ( 25 ∶75, v/v ) .This LC-MS method was established for the determination of loxoprofen in human plasma after a single oral dose administration of 60 mg loxoprofen sodium ( test preparation and reference preparation) in a crossover de- sign .RESULTS:The method is successfully validated in the pharmacokinetics study of loxoprofen in human volun- teers .The main pharmacokinetic parameters after a single dose administration of 60 mg loxoprofen sodium were as follows ( test and reference) :C_max 7 .17 ±1 .63 and 6 .94 ±13 .30 μg·ml ^-1 , T_max 0 .46 ±0 .23 and 0 .46 ±0 .28 h, AUC_{0 -10} 11 .65 ±13 .75 and 11 .19 ±18 .28 μg·ml ^-1·h, AUC_{0 -∞}12 .04 ±1 .42 and 11 .64 ±1 .89 μg·ml ^-1·h . CONCLUSION :The method is simple and readily appli- cable to routine bioavailability studies of loxoprofen sodi- um with high sensitivity and the relative bioavailability of loxoprofen sodium is ( 105 .3 ±11 .5) %.The results show that the test and reference preparation are bioequiva- lent .

Key words: loxoprofen , liqulid chromatography- mass , pharmacokinetics , bioavailability