EVALUATION OF MICRODOSING TO ASSESS PHARMACOKINETIC LINEARITY IN RATS USING LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Conventional liquid chromatography-tandem mass spectrometry (LC-MS/MS) can characterize pharmacokinetics of nonlabeled drugs at a microdose of 1 microg/kg in rats, offering a more accessible alternative to accelerator mass spectrometry (AMS) for microdosing studies. For fluconazole and tolbutamide, exposure was linear between the microdose and doses 1000-fold higher, supporting LC-MS/MS's utility in human microdosing. However, for an investigational compound MLNX, pharmacokinetics in rats were nonlinear, suggesting its microdose pharmacokinetics in humans might not reflect therapeutic doses. These findings indicate LC-MS/MS is adequate for microdose pharmacokinetic assessment in humans, though nonlinearity in some compounds may limit predictability.

Study at a glance

Abstract

The microdosing strategy allows for early assessment of human pharmacokinetics of new chemical entities using more limited safety assessment requirements than those requisite for a conventional phase I program. The current choice for evaluating microdosing is accelerator mass spectrometry (AMS) due to its ultrasensitivity for detecting radiotracers. However, the AMS technique is still expensive to be used routinely and requires the preparation of radiolabeled compounds. This report describes a feasibility study with conventional liquid chromatography-tandem mass spectrometry (LC-MS/MS) technology for oral microdosing assessment in rats, a commonly used preclinical species. The nonlabeled drugs fluconazole and tolbutamide were studied because of their similar pharmacokinetics characteristics in rats and humans. We demonstrate that pharmacokinetics can be readily characterized by LC-MS/MS at a microdose of 1 microg/kg for these molecules in rats, and, hence, LC-MS/MS should be adequate in human microdosing studies. The studies also exhibit linearity in exposure between the microdose and >or=1000-fold higher doses in rats for these drugs, which are known to show a linear dose-exposure relationship in the clinic, further substantiating the potential utility of LC-MS/MS in defining pharmacokinetics from the microdose of drugs. These data should increase confidence in the use of LC-MS/MS in microdose pharmacokinetics studies of new chemical entities in humans. Application of this approach is also described for an investigational compound, MLNX, in which the pharmacokinetics in rats were determined to be nonlinear, suggesting that MLNX pharmacokinetics at microdoses in humans also might not reflect those at the therapeutic doses. These preclinical studies demonstrate the potential applicability of using traditional LC-MS/MS for microdose pharmacokinetic assessment in humans.