PHARMACOKINETICS OF D-LIMONENE IN THE RAT BY GC-MS ASSAY

The naturally occurring monoterpene d-limonene has been found to inhib it various stages of tumorigenesis in a number of animal models and is now being evaluated as a chemopreventive agent in humans. To date, th ere are little or no preclinical pharmacokinetics available nor is the re a sensitive assay methodology. In this study, d-limonene and its di deuterium-labeled internal standard, limonene-d(2),, in whole rat bloo d were extracted with n-pentane which was then concentrated on a Kuder na-Danish concentrator. The residue was analyzed by an ion-trap GC-MS under ammonia chemical ionization. The detection limit of d-limonene w as 1.0 ng if injected in pure form however, due to the presence of end ogenous d-limonene levels (probably from diet), the routine quantitati on limit was set at 1.0 mu g ml(-1). The monitored assay linearity ran ged from 1.0 to 30 mu g ml(-1) with within-day CV values of 8.0%; 2.4% , and 2.0% at 1.0, 3.0 and 10.0 mu g ml(-1), respectively tall at n = 8), and corresponding accuracy of 100%, 100%, and 101%. The between-da y CV values were 12.3, 8.0, and 7.5% at 1, 6, and 20 mu g ml(-1), resp ectively tall at n = 8). Using this assay, pharmacokinetics of d-limon ene were studied in Sprague-Dawley rats following intravenous and oral administration at 200 mg kg(-1) each. Blood concentration-time profil es after intravenous administration showed a biphasic decline with a m ean initial t(1/2) of 12.4 min and a terminal t(1/2) of 280 min. The p lasma:red blood cell partition was found to be 0.84. Plasma protein bi nding of d-limonene was found to be 55.3% at 20 mu g ml(-1). The mean total clearance was 49.6 ml min(-1) kg(-1), the volume of distribution at steady-state 11.7 1 kg(-1), and median residence time 263 min. The blood concentration-time decline following oral administration also s howed a biphasic decline with a mean initial t(1/2) of 34 min and term inal t(1/2) of 337 min. The oral bioavailability of d-limonene was 43. 0%. (C) 1998 Elsevier Science B.V. All rights reserved.