It is an oral medication containing dofetilide as the active ingredient. The formula also contains inactive ingredients of microcrystalline cellulose, corn starch, colloidal silicon dioxide, and magnesium stearate, gelatin, titanium dioxide, and FDC Yellow 6.[1][2][3]

Clinical Uses of Dofetilide

Dofetilide is effective in maintaining sinus rhythm in patients with atrial fibrillation. In the DIAMOND studies (Torp-Pedersen C et al., 1999), dofetilide did not affect mortality in patients with advanced heart failure or those convalescing from acute myocardial infarction.

Dofetilide is indicated in adults for the conversion of atrial fibrillation or atrial flutter to normal sinus rhythm (NSR) and the preservation of normal sinus rhythm in patients with highly symptomatic atrial fibrillation or atrial flutter of more than one week whose pathological sinus rhythm has converted to normal.

Azimilide and Sematilide are also class III antiarrhythmics, but they are not available in the United States.

Because induction of severe ventricular arrhythmias is possible with dofetilide, it was available through a restricted distribution system that includes only physicians, hospitals, and other institutions that have received special educational programs covering proper dosing and in-hospital treatment initiation, which is called Risk Evaluation and Mitigation Strategy (REMS). However, in January 2016, although the safety risks for Tikosyn (dofetilide) continued to be present by FDA's determination, the agency also decided that REMS program are no longer compulsory because risk-benefit ration tilted on the side of benefits of the drug.[4]

Off-Label Uses of Dofetilide

Clinicians have used dofetilide as an off-label prescription for supraventricular arrhythmias, ventricular tachycardia, and Wolff-Parkinson-White syndrome.

Just like other class III antiarrhythmic drugs, dofetilide blocks potassium channels in phase 3 of the action potential and slows the efflux of potassium cation back out of the myocyte, which slows the repolarization rate of the cell and widens the action potential's plateau phase. The refractory periods of atrial, ventricular, and Purkinje cells thereby are increased, which also leads to lengthening of the QT interval on the ECG. The increased widening of QT interval is possibly due to the inhibition of phosphoinositide 3–kinase, which increases the late sodium current.[5][6]

Dofetilide is a class III antiarrhythmic agent. By inhibiting a component of the time-dependent potassium current, dofetilide increases the effective refractory period and action potential without affecting the conduction velocity.

Pharmacodynamics/Pharmacokinetics

Adult

Dofetilide dosing is based on creatinine clearance: (CrCl greater than 60 mL/min) 500 mcg bid (CrCl 40 mL/min to 60 mL/min) 250 mcg bid; (CrCl 20 mL/min to less than 40 mL/min) 125 mcg bid; (CrCl less than 20 mL/min) contraindicated.

Pediatric

Safety and efficacy have not been established in children.

Route of Administration

Oral absorption is approximately 100%.

Oral bioavailability is not affected by food or antacid. Steady-state plasma concentrations are attainable within 2 to 3 days. Plasma concentrations are dose-proportional.

Onset of Action

On a single dose, it takes 2 to 3 hours for dofetilide to reach maximum plasma concentration in the fasted state. Therefore, this means it takes 2 to 3 hours for the onset of action for dofetilide.

Duration of Action

The half-life of dofetilide was reported to be 4.8 to 13.5 hours. The most-reported half-life in the literature is 10 hours for dofetilide. From a pharmacokinetic principle, it takes 4.5 to 5 half-lives to eliminate approximately 100% of a single dose administration of any drug. Hence, it takes 4.5 to 5 half-lives to eliminate a single dose of dofetilide from the human body, which is 45 to 50 hours. Therefore, the duration of action of a single dose of dofetilide is 45 to 50 hours.

Distribution

The volume of distribution: 3.1 L/kg to 4.0 L/kg, indicating that dofetilide does not get sequestered in fatty tissues.

Protein Binding

Plasma protein binding of dofetilide is 60% to 70%, is independent of plasma concentration, and is unaffected by renal impairment. The volume of distribution: 3.1 L/kg to 4.0 L/kg.

Metabolism

Fifty percent of dofetilide metabolism is in the liver into inactive metabolites. Dofetilide is metabolized to a small extent by the CYP3A4 isoenzyme of the cytochrome P450 system. Inhibitors of the CYP3A4 isoenzyme could increase systemic dofetilide exposure. Inhibitors of this isoenzyme (e.g., macrolide antibiotics, azole antifungal agents, protease inhibitors, serotonin reuptake inhibitors, amiodarone, cannabinoids, diltiazem, grapefruit juice, nefazodone, norfloxacin, quinine, zafirlukast) should be cautiously coadministered with Tikosyn as they can potentially increase dofetilide levels. Dofetilide is not an inhibitor of CYP3A4 nor of other cytochrome P450 isoenzymes (e.g., CYP2C9, CYP2D6) and is not expected to increase levels of drugs metabolized by CYP3A4.

Clearance

Renal

Excretion of about 80% of a single dose of dofetilide is in urine with 80% as unchanged drug and the remaining 20% consisting of inactive or minimally active metabolites. Dofetilide gets eliminated in the kidney by cationic secretion. Inhibitors of renal cationic secretion are contraindicated with dofetilide. Also, drugs that get actively secreted via this route (e.g., triamterene, metformin, and amiloride) should be co-administered with care as they might increase dofetilide levels. Elimination half-life is 4.8 to 13.5 hours.

The drug has virtually no extracardiac pharmacological effects.[7]

Torsades de pointes occurred in 1% to 3% of patients in clinical trials where strict exclusion criteria (e.g., hypokalemia) were applied, and continuous ECG monitoring was used to detect marked QT prolongation in the hospital.

With therapeutic use, dofetilide may induce or worsen ventricular dysrhythmias, producing life-threatening polymorphic ventricular tachycardia. Patients with a history of torsade de pointes, prolonged QTc (greater than 440 milliseconds), hypomagnesemia, or serum potassium below 4.0 mEq/L are at increased risk of developing ventricular dysrhythmias. Other adverse effects that may occur with dofetilide administration include chest pain, nausea, abdominal pain, flatulence, diarrhea, headache, dizziness, and fatigue.

Overdose experience is limited. Effects reported include QT prolongation, torsade de pointes, and complete heart block. Most common side effects are a headache, chest pain, and dizziness.

Adverse Reactions Severe

• Fast, pounding, or irregular heartbeat
• Rash
• Severe diarrhea
• Dizziness or fainting
• Unusual sweating
• Vomiting
• Loss of appetite
• Increased thirst (drinking more than normal)

Adverse Reactions Mild

• Headache
• Chest pain
• Shortness of breath
• Nausea
• Flu-like symptoms
• Stomach pain
• Back pain
• Difficulty falling asleep or staying asleep

Pregnancy

Dofetilide classified as FDA pregnancy category C under the recently replaced system. Therefore, pregnant patients should not receive dofetilide.

Drug Interactions

Approximately 80% of a single dose of dofetilide gets excreted in the urine, of which approximately 80% is excreted as unchanged dofetilide with the remaining 20% consisting of inactive or minimally active metabolites. Renal elimination involves both glomerular filtration and active tubular secretion (via the cation transport system, a process that can be inhibited by cimetidine, trimethoprim, prochlorperazine, megestrol, ketoconazole, and dolutegravir). In vitro studies with human liver microsomes show that CYP3A4 can metabolize dofetilide, but it has a low affinity for this isoenzyme. N-dealkylation and N-oxidation form metabolites.

The following list of drugs are known to have significant interactions with dofetilide by inhibiting renal elimination:

• Cimetidine
• Verapamil
•  Ketoconazole
• Trimethoprim alone or in combination with sulfamethoxazole
• Prochlorperazine
• Megestrol
• Dolutegravir
• Hydrochlorothiazide alone or in combination with other medicines

Dofetilide contraindications include patients with long QT syndrome. It is also contraindicated in patients who are on kidney dialysis or have renal diseases.

Dofetilide is contraindicated in patients having a low level of potassium in the blood, vomiting and/or diarrhea, sweating, loss of appetite, or decreased thirst, and whether the patients have or have ever had have heart or liver disease. Dofetilide is contraindicated in patients planning to become pregnant, pregnant, or who are breastfeeding.