A Rapid and Simple UHPLC-UV Method for Quantitative Determination of Erlotinib and Its Active Metabolite OSI-420 in Human Serum, and Its Application in a Non-Small Cell Lung Cancer Patient

We developed a rapid and simple UHPLC-UV method for quantitative determination of erlotinib and its metabolite, OSI-420, in order to monitor their serum levels in patients with non-small cell lung cancer (NSCLC). Erlotinib and OSI-420 were extracted from 100 μL of human serum by liquid–liquid extraction using t-butyl methyl ether. The analytes were separated on Inertsil ODS-3 (100 mm × 2.1 mm I.D., 2 μm) as an analytical column using 20 mM potassium phosphate buffer (pH 2.5)/acetonitrile (74:26, v/v) as the mobile phase at a flow rate of 0.6 mL/min, and monitored at a UV wavelength of 345 nm. This method covered a linear concentration range of 6–6000 ng/mL for erlotinib and 6–2000 ng/mL for OSI-420, respectively (r > 0.999). The intra- and inter-day precisions of the analysis were < 6.8%, and the accuracy was ± 7.4%. This method has been successfully applied to measure erlotinib and OSI-420 in the serum of an NSCLC patient.