Quantitative in Vivo Microsampling for Pharmacokinetic Studies Based on an Integrated Solid-Phase Microextraction System

Abstract

An integrated microsampling approach based on solid-phase microextraction (SPME) was developed to provide a complete solution to highly efficient and accurate pharmacokinetic studies. The microsampling system included SPME probes that are made of poly(ethylene glycol) (PEG) and C18-bonded silica, a fast and efficient sampling strategy with accurate kinetic calibration, and a high-throughput desorption device based on a modified 96-well plate. The sampling system greatly improved the quantitative capability of SPME in two ways. First, the use of the C18-bonded silica/PEG fibers minimized the competition effect from analogues of the target analytes in a complicated sample matrix such as blood or plasma samples, which is a common problem associated with solid coating SPME fibers for quantitative analysis. Moreover, the C18-bonded silica/PEG fibers provide high sensitivity and a large dynamic range that covers the possible sample concentration range during diazepam administration and elimination. Second, the kinetic calibration method offers more accurate quantitation than the calibration curve method for in vivo SPME, because it compensates for convection and matrix effects during sampling. Therefore, it is especially suitable as a fast sampling technique for pre-equilibrium SPME. Furthermore, with the high-throughput desorption device, the integrated system offers compactness and high efficiency. Its feasibility for in vivo sampling was demonstrated by monitoring diazepam pharmacokinetics and validated by conventional chemical assays and equilibrium SPME. In addition, we propose a simple method to determine the apparent distribution constant between an SPME fiber and a blood matix (Kfs) and the distribution constant between an SPME fiber and a pure PBS buffer sample matrix (Kfb). As a result, both total and free concentrations of the drug and its metabolites can be detected simultaneously. Accordingly, the binding constants to the blood matrix can be obtained, which are of special significance for clinical diagnosis and drug discovery.

Current Developments and Future Trends in Solid-phase Microextraction Techniques for Pharmaceutical and Biomedical Analyses

“…The method has been successfully utilized for the in vivo and in vitro pharmacokinetic measurements of free concentrations of ligand. 113,[117][118][119][120][121][122][123][124][125] Whole-blood and free concentrations of ligand, easily measured by SPME, are of utmost importance in therapeutics, since they correlate with the pharmacological effects of drug and are more significant than plasma concentrations. Using PDMS and PA coatings, the binding of several drugs with different polarities and binding constants to human plasma and serum albumin has been determined, indicating that this method is thermodynamically sound, requiring a small volume of sample and a short analysis time.…”

“…24,25,27,30,35,39,40,87,[117][118][119][120][121][122][123][124][125] Two configurations of proposed in vivo SPME sampling systems are illustrated (Fig. 4).…”

“…Direct exposure devices must incorporate a mechanically strong, flexible and unbreakable fiber core, and their materials must be biocompatible so as to avoid toxic reactions caused by direct exposure to biological sample and to minimize the possibility of surface fouling of the coating during the short experimental sampling times. This may be achieved by covering the surface of the sorbent with a known biocompatible polymer, such as polypyrrole, 117 polyethylene glycol 120,121 or polyacrylonitrile, 87 which permits the diffusion of low-molecular weight analytes to the sorbent, while excluding high-molecular weight species, such as proteins. In vivo SPME probes have diameters ranging over 100 -200 μm, the coating thicknesses ranging over 5 -200 μm and coating lengths varying from 1 -15 mm.…”

“…Modified devices with 1 -2 cm long coatings housed inside a hypodermic needle can be particularly useful, and the small dimensions of these devices minimize tissue damage. In vivo SPME sampling [119][120][121][122][123] of flowing blood is faster than the current methods based on drawing blood, with the former having sampling times of 2 min for external calibration and 30 s for standard on fiber approaches.…”

“…For example, these fibers were used in the in vivo pharmacokinetic determination of diazepam and carbamazepine in rats and mice. [119][120][121][122]125 The catheters were plugged and exteriorized at the nape of the neck, with the lower tube of the interface connected to the carotid artery catheter, and the upper tube of the interface either recirculated to the carotid artery catheter or connected to a syringe. After administration of a drug by bolus injection into the jugular carotid artery catheter, the SPME device was placed through the septum into the interface and exposed to flowing blood, and the drug and its metabolites were analyzed by LC-MS/MS.…”