Quantitative LC-ToF MS analyses of dried blood spots: Developing an assessment of medication adherence for heart disease patients

Abstract

Introduction: Over 355 million prescriptions were dispensed for cardiovascular diseases in the UK in 20131. Half of these, costing the NHS £2.3 billion, were wasted because patients did not take their medicines as prescribed2. A method using dried blood spot (DBS) sample collection followed by liquid chromatography-time of flight mass spectrometry (LC-ToF MS) analyses3,4 was developed and validated for quantification of 8 commonly UK prescribed cardiovascular drugs: atenolol, bisoprolol, diltiazem, doxazosin, losartan, ramipril, simvastatin and valsartan. Thus medication effectiveness, adherence or drug/drug interactions can be assessed from reference pharmacokinetic data. Methods: For the preparation of DBS calibration samples whole blood was spiked with 8 target analytes to produce 30µl blood spots on specimen cards. 8mm disc was punched out and extracted with methanol:water (70:30v/v) containing the internal standard, atenolol D7. Chromatography analysis was performed using gradient elution with a run time of 2.5 min. High resolution MS detection was carried out using electrospray positive ion mode for all target analytes and internal standard. Results: The LC-ToF MS method validation showed good linearity and the accuracy (relative error) and precision (coefficient of variation) values were within the pre-defined limits of ≤15% at all tested concentrations for the 8 target drugs. Drug recoveries from spiked blood spots were ≥ 82% for atenolol, bisoprolol, diltiazem, doxazosin, losartan, ramipril and valsartan. Results from DBS samples from volunteers were within expected levels with respect to published pharmacokinetic data except where elevated levels indicated a recognised drug/drug interaction. Conclusions: Quantitative DBS analyses using LC-ToF MS has the potential to both assess medication adherence and to allow re-interrogation of data collected for heart disease patients.