A simple, high-throughput LC-MS/MS method for the simultaneous quantification of four antiarrhythmic drugs and two...

Therapeutic drug monitoring (TDM) of antiarrhythmic drugs (AADs) remains underutilized in clinical practice despite the narrow therapeutic windows and marked inter-individual pharmacokinetic variability of these agents. Here, we developed and validated a simple, high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of four commonly prescribed AADs-amiodarone, dronedarone, flecainide, and propafenone-and two metabolites, noramiodarone and debutyldronedarone, in human serum, and applied it to routine clinical samples. Sample preparation consisted of simple protein precipitation using only 10 μL of serum, with a 2 μL injection volume and a total run time of 5.7 min. The method showed excellent linearity for all analytes (R² > 0.99), acceptable precision (%CV 0.9-5.9%) and accuracy (%bias -6.5-10.5%), minimal matrix effects (88.1-106.6%), satisfactory extraction recoveries (93.9-104.1%), and no significant carryover. No exogenous interference was observed from 25 commonly co-administered cardiovascular drugs, or from 45 neuropsychiatric drugs. The validated assay was successfully applied to 622 serum samples from 524 Korean patients with various arrhythmias. AAD concentrations showed substantial inter-individual variability at identical daily doses, and high proportions of samples were below the therapeutic ranges, supporting the potential utility of routine AAD TDM. This LC-MS/MS method provides a rapid, robust, and clinically practical platform for routine individualized AAD TDM in real-world serum samples with complex matrices.