Solid-phase microextraction for assessment of plasma protein binding, a complement to rapid equilibrium dialysis.

Aim: Determination of plasma protein binding (PPB) is considered vital for better understanding of pharmacokinetic and pharmacodynamic activities of drugs due to the role of free concentration in pharmacological response. Methodology & results: Solid-phase microextraction (SPME) was investigated for measurement of PPB from biological matrices and compared with a gold standard approach (rapid equilibrium dialysis [RED]). Discussion & conclusion: SPME-derived values of PPB correlated well with literature values, and those determined by RED. Respectively, average protein binding across three concentrations by RED and SPME was 33.1 and 31.7% for metoprolol, 89.0 and 86.6% for propranolol and 99.2 and 99.0% for diclofenac. This study generates some evidence for SPME as an alternative platform for the determination of PPB.

Direct ionization of solid-phase microextraction fibers for quantitative drug bioanalysis: from peripheral circulation to mass spectrometry detection.

A novel approach is described for the quantitative bioanalysis of drugs in blood samples by ionization of the analytes collected on solid-phase microextraction (SPME) fibers by mass spectrometry (MS). The technique combines the attractive features of SPME microsampling using minimal sample volumes with the speed, selectivity, and sensitivity capabilities of MS detection. The method reported in this study involved generating gas-phase ions directly from SPME fibers without the need for any additional sample preparation or chromatographic separation; the entire process was completed within 5 min. Traditionally, analytes extracted by SPME fibers are desorbed by washing with suitable solvents followed by a transfer into a sample vial and subsequent liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to quantify the amount of analyte extracted and thereby determining the analyte concentration in the matrix. These sample preparation steps are completely eliminated by inserting the SPME fiber directly into the MS. Physiologically relevant concentrations of metoprolol and propranolol in blood samples were measured over several orders of magnitude down to concentration levels of 10 ng/mL. This preliminary assessment of direct SPME-MS showed high sensitivity (ng/mL), acceptable reproducibility (<30%), and lack of carryover. This novel approach simplifies current bioanalytical procedures providing time and cost savings. It demonstrates considerable potential for qualitative and quantitative pharmaceutical bioanalysis as well as other areas of challenging environmental and food analysis.

Is SPME a destination or just another station for bioanalysis?

This article reviews the solid-phase microextraction technique and its potential to revolutionize bioanalysis in terms of combining sampling, sample preparation and extraction in one step with no blood withdrawal. Possible hurdles facing the technology when implemented in a pharmaceutical setting will be covered and the author will provide an outlook on the future of solid-phase microextraction as a novel microsampling technique for bioanalysis.

Assessment of the within- and between-lot variability of Whatman™ FTA(®) DMPK and 903(®) DBS papers and their suitability for the quantitative bioanalysis of small molecules.

BACKGROUND: To ensure that PK data generated from DBS samples are of the highest quality, it is important that the paper substrate is uniform and does not unduly contribute to variability. This study investigated any within and between lot variations for four cellulose paper types: Whatman™ FTA(®) DMPK-A, -B and -C, and 903(®) (GE Healthcare, Buckinghamshire, UK). The substrates were tested to demonstrate manufacturing reproducibility (thickness, weight, chemical coating concentration) and its effect on the size of the DBS produced, and the quantitative data derived from the bioanalysis of human DBS samples containing six compounds of varying physicochemical properties. RESULTS & DISCUSSION: Within and between lot variations in paper thickness, mass and chemical coating concentration were within acceptable manufacturing limits. No variation in the spot size or bioanalytical data was observed. CONCLUSION: Bioanalytical results obtained for DBS samples containing a number of analytes spanning a range of chemical space are not affected by the lot used or by the location within a lot.

GlaxoSmithKline's experience of incurred sample reanalysis for dried blood spot samples.

Dried blood spots are becoming a popular alternative to plasma for many different applications. This has been driven by animal ethics but also by ease of use and cost savings. Recent regulatory guidance now has a requirement for incurred sample reanalysis. This article details three examples of incurred sample reanalysis using dried blood spot samples.