A new HPLC-UV method was developed and validated for the quantitative determination of epidermal growth factor receptor inhibitor erlotinib in the plasma of tumor bearing BALB/c nude mice.Erlotinib and its internal standard l-（3-（（6,7-bis（2- methoxyethoxy）quinazolin-4-yl）amino）phenyl）ethanone were extracted from mice plasma samples using liquid-liquid extraction with a mixed solvent of methyl t-butyl ether and ethyl acetate（9：1,v/v）.Chromatographic separation was performed on a Luna C｜_（18）column（4.6 mm×250 mm,5μm）with acetonitrile：5 mM potassium phosphate buffer pH=5.2（41：59,v/v）as the mobile phase.UV detector was set at the wavelength of 345 nm,and the flow rate was 1.0 mL/min.The calibration curve was linear over the range of 20-10 000 ng/mL with acceptable intra-and inter-day precision and accuracy.The intra-day and inter-day precisions were within the range of 1.69%—5.66%,and the accuracies of intra-and inter-day assays were within the range of 105%—113%. The mean recoveries were 85.2%and 96.1%for erlotinib and IS,respectively.This method was successfully applied to a pharmacokinetic study in tumor bearing BALB/c nude mice following single oral administration at the dose of 12.5 mg/kg. The main pharmacokinetic parameters were as follows：C_（max）was 4.67μg/mL,T_（max）was 1.0 h,T_（1/2）was 2.78 h,and AUC_（0-24h）was 18.0μg/mL·h.
A simple, rapid and sensitive LC-MS/MS method was developed to quantify erlotinib and its active metabolite, OSI-420, simultaneously in BALB/c nude mice plasma. Erlotinib, OSI-420 and propranolol （internal standard） were extracted from nude mice plasma samples by liquid-liquid extraction. Separation was achieved on a reversed phase ClS column with a mobile phase of acetonitrile-water （35：65, v/v） containing 5 mM ammonium formate （pH = 3.0）. All compounds were monitored by mass spectrometry with electrospray positive ionization. The lower limit of quantification was 0.5 ng/mL for both erlotinib and OSI-420; accuracy was estimated by relative error, which was in the range from 0.07% to 8.00% for erlotinib and -2.83% to 6.67% for OSI-420; precision was validated by relative standard deviation, which was from 2.28% to 15.12% for erlotinib and from 1.96% to 11.50% for OSI-420. This method was applied to a pharmacokinetic study of BALB/c nude mice following oral administration of erlotinib at 12.5 mg/kg. A 2-compartment model was used to fit the pharmacokinetics of erlotinib and 1-compartment model for the pharmacokinetics of OSI-420. The ratio of the active metabolite to parent drug in mice was greater than previously reported in humans and probably reflects interspecies difference in the rate of conversion of erlotinib to OSI-420.
