Dofetilide-d4 is intended for use as an internal standard for the quantification of dofetilide by GC- or LC-MS. Dofetilide is a class III antiarrhythmic agent that prolongs cardiac action potential duration by selectively inhibiting the rapidly activating inward rectifying component of net delayed rectifier K+ current (IC50 = 31.5 nM in guinea pig cardiomyocytes). However, at 1 μM, dofetilide has pro-arrhythmic activity, inducing early afterdepolarizations (prolonged repolarization) in cell models and Torsade de Pointes in a rabbit screen for proarrhythmic properties when administered at a dose of 10 mg/kg. Formulations containing dofetilide have been used in the treatment of highly symptomatic atrial fibrillation and the conversion of flutter to normal sinus rhythm.
