Quantitative LC-HRMS determination of selected cardiovascular drugs, in dried blood spots, as an indicator of adherence to medication

Dried blood spot (DBS) sampling was investigated as a means of obtaining micro-volume blood samples for the quantitative analyses of ten commonly UK prescribed cardiovascular drugs as an indicator of medication adherence. An 8mm disc was punched out from each DBS from calibration, quality control and volunteer samples and extracted using methanol containing the internal standard. Each extract was evaporated to dryness, the residue reconstituted in methanol:water (40:60v/v) containing 0.1% formic acid and analysed by LC-HRMS. Chromatography was performed using gradient elution on a Zorbax Eclipse C18 HD 100mm×2.1mm, 1.8μm pore size column with the column oven temperature at 40°C. Flow rate of the mobile phase was 0.6ml/min with a run time of 2.5min. Electrospray positive ionization was used for MS detection. Drug recoveries from spiked blood spots were 68% for simvastatin and ≥87% for all other target drugs. Compound specificity was obtained operating the MS with a 5ppm mass window. The LC-HRMS method was validated, with results for accuracy and precision within acceptable limits; analytes were stable at room temperature for at least 10 weeks and different blood spot volumes and haematocrit values had no significant effect. The LC-HRMS assay was used to analyse DBS samples from volunteers, some of whom were prescribed one or more of the target drugs. In results from 37 volunteers the assay successfully identified volunteers who were known to be either adherent or nonadherent; confirmed the correct drug/drugs for multiple prescriptions; demonstrated no false positives from other cardiovascular drugs; revealed several examples of unsuspected non-adherence. These results indicated that the developed assay was suitable for trials with patients.