Introduction: Verapamil (Verap) is an antidysrhythmic agent and a calcium channel blocker, indicated for angina, hypertension, supraventricular arrhythmias, and migraine. Objective: Drug monitoring plays a critical role in patient survival. In order to prevent the onset of drug toxicity, trace levels of this drug should be determined. Method: For this reason, solvent bar microextraction technique coupled with high-performance liquid chromatography was implemented. Results: Under optimum condition, verapamil was micro-extracted from a donor solution (pH=11) to an acceptor solution (pH=3.2). It was transferred through n-octanol as the organic solvent, which was impregnated in the pores of the hollow fiber. Salt addition (30%) had the major effect on the efficiency of the method. Interaction of time (65 min), temperature (25°C), and stirring rate (818 rpm) had a significant effect too. It all resulted in a limit of detection and quantification of 15 ng mL-1 and 50 ng mL-1, respectively. The relative standard deviations of analysis were 4.9% within a day (n=3) and 5.7% between days (n=9). The calibration curves represented good linearity for urine and plasma samples with coefficient estimations higher than 0.99 with a linearity range of 50-5000 ng mL-1. The relative standard deviation for intra- (n=3) and inter-(n=9) day was 4.2% and 5.7%, respectively. Conclusion: It could be concluded that the application of this method for dose monitoring can be done at hospital and healthcare facilities.
Keywords: Verapamil, Solvent bar, Microexteraction, Minitab, HPLC-UV