Evaluation of bio-compatible poly(ethylene glycol)-based solid-phase microextraction fiber for in vivo pharmacokinetic studies of diazepam in dogs

Abstract

Solid-phase microextraction probes based on poly(ethylene glycol)/C18-bonded silica were used for in vivo monitoring of drugs from circulating blood of beagles, over a period of 8 h. After sampling, the extracted drugs were subsequently quantified by liquid chromatography coupled with tandem mass spectrometry. External calibrations in whole blood and phosphate-buffered saline were used to correlate the amount of analytes extracted in regard to the total and free concentrations in blood respectively. The probe provided sufficient sensitivity for the drugs in the blood matrix, while the need for drawing blood was eliminated. The limit of detections of the method from whole blood were 1.7, 1.4 and 2.8 ng mL(-1) for the analysis of diazepam, nordiazepam and oxazepam respectively, and the linear range was from 4 ng mL(-1) to 2 microg mL(-1). The method was applied for the monitoring of pharmacokinetic profiles of intravenous administration of diazepam and its two main metabolites in dogs, and the results were compared with profiles determined by conventional methods. This approach offered increased sensitivity and accuracy, short extraction time, and convenient calibration for in vivo sampling for dynamic monitoring.

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

“…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.…”

“…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).…”

“…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.…”

“…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.…”

Making biosamples compatible with instrumental analysis

“…In addition, the microextraction does not change the system equilibrium since the amount of extracted analyte is very low. Although this approach has been mainly used with animals [22,23] probably due to ethical reasons, it has a great potential in humans as it has been outlined in a recent communication [24].…”