be more common in individuals also taking digoxin, possibly because of pre-existing heart failure in those people. As with other beta blockers, it may interact with calcium channel blockers, catecholamine-depleting drugs, insulin or antidiabetic drugs, beta2-adrenergic agonists, and clonidine. Some evidence suggests that sotalol should be avoided in the setting of heart failure with a reduced ejection fraction (resulting in the heart squeezing little blood out into the circulation with each pump) due to an increased risk of death. Adverse effects Over 10% of oral sotalol users experience fatigue, dizziness, lightheadedness, headache, weakness, nausea, shortness of breath, bradycardia (slow heart rate), a sensation of the heart beating too hard, fast, or irregularly, or chest pain. Higher doses of sotalol increase the risk for all of these possible side effects. In rare cases, the QT prolongation caused by sotalol can lead to the development of life-threatening torsade de pointes (TdP) polymorphic ventricular tachycardia. Across several clinical trials, 0.6% of oral sotalol patients with supraventricular abnormal heart rhythms (such as atrial fibrillation) developed TdP. For patients who had a history of sustained ventricular tachycardia (abnormal rhythm lasting more than 30 seconds), 4% developed TdP. Risk increases with dosage, female sex, or having a history of an enlarged heart or congestive heart failure. The incidence of TdP for sustained ventricular tachycardia patients was 0% with an 80 mg daily dose, 0.5% at 160 mg, 1.6% at 320 mg, 4.4% at 480 mg, 3.7% at 640 mg, and 5.8% at doses greater than 640 mg. Due to this risk, the U.S. Food and Drug Administration requires affected individuals to be hospitalized for at least three days in a facility that can provide cardiac resuscitation and continuous electrocardiographic monitoring upon starting or restarting sotalol. Mechanisms of action Beta-blocker action Sotalol non-selectively binds to both β1- and β2-adrenergic receptors preventing activation of the receptors by their stimulatory ligand (catecholamines). Without the binding of this ligand to the receptor, the G-protein complex associated with the receptor cannot activate production of cyclic AMP, which is responsible for turning on calcium inflow channels. A decrease in activation of calcium channels will therefore result in a decrease in intracellular calcium. In heart cells, calcium is important in generating electrical signals for heart muscle contraction, as well as generating force for this contraction. In consideration of these important properties of calcium, two conclusions can be drawn. First, with less calcium in