Simultaneous GC-MS determination of nicotine and cotinine in plasma for the pharmacokinetic characterization of nicotine in rats

A gas-liquid chromatography/mass spectrometry assay method was developed for the simultaneous determination of nicotine and its major metabolite, cotinine, in rat plasma. Of particular interest was improving the low and variable extraction recovery for the parent drug and the metabolite. In addition, the feasibility of this assay method for pharmacokinetic studies of nicotine and cotinine after intravenous (iv), oral, and intraperitoneal (ip) administration of 1 mg kg(-1) of nicotine was tested. The low (30 and 48% for nicotine and cotinine, respectively) and variable (25 and 22% coefficient of Variation for nicotine and cotinine, respectively) extraction recovery for nicotine and cotinine into dichloromethane was significantly improved by the addition of NaCl to the plasma. As a result, the recoveries for nicotine and cotinine were improved to 68 and 65%, respectively. The coefficient of variation was less than 10% in the 50-500 ng ml(-1) range and less than 16.58% at 10 ng ml(-1) for both nicotine and cotinine, indicating that the reproducibility of the assay was also improved by the extraction procedure. When injected intravenously at a dose of 1 mg kg(-1), the temporal profile of plasma concentration for nicotine followed a bi-exponential decline. Moment analysis revealed that pharmacokinetic parameters for nicotine (i.e. Cl, 46.30 ml min(-1) kg(-1); V-ss, 2.77 l kg(-1)) was similar to those reported in studies using C-14-nicotine. Absolute bioavailabilties of nicotine for ip and oral administration were 87.0 and 80.4%, respectively. The concentration of the metabolite increased up to 4 h to reach C-max after ip and oral administrations and then declined slowly with time. These results indicate that this convenient analytical procedure is readily applicable to pharmacokinetic studies of nicotine and cotinine involving small laboratory animals with a sensitivity comparable with that reported for studies using C-14-nicotine. (C) 1999 Elsevier Science B.V. All rights reserved.