High performance liquid chromatographic determination of cyclooxygenase II inhibitor rofecoxib in rat and human plasma.J Pharm Pharm Sci. 2000 Sep-Dec; 3(3):312-7.JP
Rofecoxib is a relatively new non-steroidal anti-inflammatory drug with high selectivity in cyclooxygenase 2 inhibitory activity. There is only one assay reported for determination of the drug in biological samples. The assay requires a post-column UV reactor for photocyclization before detection with fluorescence detector. In addition, the internal standard (IS) used in the assay in not commercially available. We developed a new assay for determination of rofecoxib. Rat blank plasma (200 microL) or human blank plasma (500 microL) was spiked with rofecoxib to make final concentrations of 10 to 3000 ng/mL, and 100 microl of a 2 microg/mL of ketoprofen as IS, 100 microl of a pH 4.5 acetate buffer, and 6 mL of ethyl acetate were added. The resultant was vortex-mixed for 90 seconds and centrifuged at 2500 g for 3 min. The organic layer was separated and evaporated to dryness under vacuum. The residues were reconstituted in 170 microL of mobile phase and 150 microL was injected into an HPLC consisting of an autoinjector, an isocratic pump, a 10 cm 4.6 i.d. C(18) analytical column packed with 5 microm reversed phase particles, a variable UV spectrophotometer detector set at 272 nm, and an integrator. The mobile phase consisted of water (77%), acetonitrile (23%), acetic acid (0.1%), and triethylamine (0.03%) and was pumped at 1 mL/min at ambient temperature. The drug and IS were eluted at 13 and 24 min, respectively. The peak drug/IS area ratio versus drug concentrations relationship was linear (r>0.99). The extraction efficiency was >87%. The minimum quantifiable concentration was set at 10 ng/mL (correlation coefficient of <10%). This convenient, sensitive, and simple method is suitable to pharmacokinetic studies of rofecoxib in rats and humans.