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[Determination of lornoxicam in human plasma by LC/MS/MS].

AIM
To develop a sensitive and specific LC/MS/MS method for determination of lornoxicam in human plasma and investigate pharmacokinetics of single dose of lornoxicam in healthy Chinese volunteers.


METHODS
Lornoxicam and the internal standard piroxicam were extracted from plasma using liquid-liquid extraction, then separated on a Zorbax XDB-C8 column. The mobile phase consisted of methanol-water-formic acid (80:20:0.5) at a flow-rate of 0.7 mL.min-1. A Finnigan TSQ tandem mass spectrometer equipped with atmospheric pressure chemical ionization source was used as detector and operated in the positive ion mode. Selected reaction monitoring (SRM) using the precursor-->product ion combinations of m/z 372-->121 and m/z 332-->121 was used to quantify lornoxicam and internal standard, respectively.


RESULTS
The linear calibration curves were obtained in the concentration range of 2.0-1,600 micrograms.L-1. The limit of quantitation was 2.0 micrograms.L-1. The method was successfully used in the pharmacokinetic study for lornoxicam. The main parameters obtained after an oral dose of 8 mg lornoxicam to 18 Chinese male volunteers were as follows: the value of T1/2 was (4.7 +/- 1.1) h, AUC0-infinity was found to be (5.5 +/- 2.4) mg.h.L-1. However, T1/2 of 105 h and AUC0-infinity of 189.5 mg.h.L-1 were obtained for another volunteer.


CONCLUSION
The method is proved to be suitable for clinical investigation of lornoxicam pharmacokinetics, which offers advantages of specificity, speed, and higher sensitivity over the previously reported methods.