Flecainide, marketed under trade names such as Almarytm, Apocard, Ecrinal, and Flécaine, is a class Ic antiarrhythmic drug used to prevent and treat a variety of cardiac arrhythmias. This Certified Spiking Solution® is suitable for use as a starting material in the preparation of calibrators, controls, or linearity standards in flecainide therapeutic drug monitoring methods by LC/MS or LC that ensure patients remain within the drug’s narrow therapeutic range.