Development and Evaluation of a Solid-Phase Microextraction Probe for in Vivo Pharmacokinetic Studies

Simplified procedures and a reduction in sampling errors are important advantages for performing as many chemical analysis steps as possible at the site where a sample or subject is located. Solid-phase microextraction technology addresses this goal, and for our purposes, it also allows for in vivo monitoring of a dynamic living system with minimal disturbance of the system. Here we report the development of a solid-phase microextraction application for in vivo monitoring of circulating blood concentrations of benzodiazepines. A probe based on a polypyrrole extraction phase was developed and used for extraction of drug molecules directly from a peripheral vein with subsequent instrumental quantification. The probe provides good sensitivity and selectivity for the drugs versus the blood matrix, while eliminating the need to draw blood. After sampling, the extracted drugs are quantified by liquid chromatography-tandem mass spectrometry. The limit of detection of the method is ~3-7 ng/mL for analysis of the benzodiazepines from whole blood, and the method is linear to 1000 ng/mL. The method was used to monitor the pharmacokinetic profiles of diazepam and its metabolites in dogs, and the results compared favorably with profiles determined by conventional methods. Because no blood and only very small amounts of drugs are removed, minimal disruption to the chemical balance in blood occurs. This approach offers the potential for reduced exposure to blood for analytical personnel, simplified, less disruptive sampling, and lower stress levels on animals for pharmacokinetic studies. It also allows for a significant reduction in animal usage for these studies, which is important both ethically and for improving data quality.