AHFS/Drugs.com Monograph ATC code C01BD04 (WHO) Protein binding 60% -70% CAS ID 115256-11-6 | MedlinePlus a601235 Bioavailability 96% (oral) Biological half-life 10 hours Molar mass 441.567 g/mol | |
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Dofetilide is a class III antiarrhythmic agent. It is marketed under the trade name Tikosyn by Pfizer, and is available in the United States in capsules containing 125, 250, and 500 µg of dofetilide. It is not available in Europe or Australia.
Contents
Due to the pro-arrhythmic potential of dofetilide, it is only available by prescription from physicians who have undergone specific training in the risks of treatment with dofetilide. In addition, it is only available by mail order or through specially trained local pharmacies.
Uses
Dofetilide is used for the maintenance of sinus rhythm in individuals prone to the occurrence of atrial fibrillation and flutter arrhythmias, and for chemical cardioversion to sinus rhythm from atrial fibrillation and flutter.
Pharmacokinetics
Dofetilide is well absorbed in its oral form, with a bioavailability of >90%.
The elimination half-life of dofetilide is roughly 10 hours; however, this varies based on many physiologic factors (most significantly creatinine clearance), and ranges from 4.8 to 13.5 hours. Due to the significant level of renal elimination (80% unchanged, 20% metabolites), the dose of dofetilide must be adjusted to prevent toxicity due to impaired renal function.
Mechanism of action
Dofetilide works by selectively blocking the rapid component of the delayed rectifier outward potassium current (IKr).
This causes the refractory period of atrial tissue to increase, hence its effectiveness in the treatment of atrial fibrillation and atrial flutter.
Dofetilide does not affect Vmax (the slope of the upstroke of phase 0 depolarization), conduction velocity, or the resting membrane potential.
There is a dose-dependent increase in the QT interval and the corrected QT interval (QTc). Because of this, many practitioners will initiate dofetilide therapy only on individuals under telemetry monitoring or if serial EKG measurements of QT and QTc can be performed.
Metabolism
A steady-state plasma level of dofetilide is achieved in 2–3 days.
80% of dofetilide is excreted by the kidneys, so the dose of dofetilide should be adjusted in individuals with renal insufficiency, based on creatinine clearance.
In the kidneys, dofetilide is eliminated via cation exchange (secretion). Agents that interfere with the renal cation exchange system, such as verapamil, cimetidine, hydrochlorothiazide, itraconazole, ketoconazole, prochlorperazine, and trimethoprim should not be administered to individuals taking dofetilide.
About 20 percent of dofetilide is metabolized in the liver via the CYP3A4 isoenzyme of the cytochrome P450 enzyme system. Drugs that interfere with the activity of the CYP3A4 isoenzyme can increase serum dofetilide levels. If the renal cation exchange system is interfered with (as with the medications listed above), a larger percentage of dofetilide is cleared via the CYP3A4 isoenzyme system.
Side effects
Torsades de pointes is the most serious side effect of dofetilide therapy. The incidence of torsades de pointes is 0.3-10.5% and is dose-related, with increased incidence associated with higher doses.
The risk of inducing torsades de pointes can be decreased by taking precautions when initiating therapy, such as hospitalizing individuals for a minimum of three days for serial creatinine measurement, continuous telemetry monitoring and availability of cardiac resuscitation.
Clinical use
Based on the results of the Danish Investigations of Arrhythmias and Mortality on Dofetilide ("DIAMOND") study, dofetilide does not affect mortality in the treatment of patients post-myocardial infarction with left ventricular dysfunction, however it was shown to decrease all-cause readmissions as well as CHF-related readmissions. Because of the results of the DIAMOND study, some physicians use dofetilide in the suppression of atrial fibrillation in individuals with LV dysfunction, however use appears limited: After initially receiving marketing approval in Europe in 1999, Pfizer voluntarily withdrew this approval in 2004 for commercial reasons and it is not registered in other first world countries. It has clinical advantages over other class III antiarrythmics in chemical cardioversion of atrial fibrillation, and maintenance of sinus rhythm, and does not have the pulmonary or hepatotoxicity of amiodarone, however atrial fibrillation is not generally considered life-threatening, and dofetilide causes an increased rate of potentially life-threatening arryrthmias in comparison to other therapies.