Investigation of possible interference of a metabolite of etoricoxib (Arcoxia®) in the detection of 16a-hydroxyprednisolone by LC-MS/MS

Abstract

Etoricoxib (Arcoxia®) is a recent drug for the effective treatment of pain, inflammation and fever. It is available without prescription in Thailand but may require a physician’s prescription in other countries. This investigation was initiated by the presence of a large peak in about 10% of the MRM chromatograms of our screening procedure for corticosteroids by LC-MS/MS. This peak was in the time window of the MRM transition for 16a-hydroxyprednisolone. Fortunately for some of these samples the data sheet for previous use of medication stated the use of Arcoxia®. To confirm that the interfering peak was due to a metabolite of the drug etoricoxib (Arcoxia®) an excretion study of a male volunteer who had taken a 30-mg single oral dose of etoricoxib was performed. Metabolites of the drug were identified by comparison of the observed mass spectra (both full scan and product ion scan) with that reported in the literature. It was shown that the interference peak was 6’-hydroxymethyl-etoricoxib. The mass spectrum information of this metabolite was then used to modify the MRM transition for 16a-hydroxyprednisolone in the screening method.