Propafenone

Propafenone (pro-PA-fen-own) (brand name Rythmol SR®) is a class Ic anti-arrhythmic medication, which treats illnesses associated with rapid heart beats such as atrial and ventricular arrhythmias.

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Mechanism of action

Propafenone works by slowing the influx of sodium ions into the cardiac muscle cells, causing a decrease in excitability of the cells.

Metabolism

Propafenone is metabolized primarily in the liver. Because of its short half-life, it requires dosing two or three times daily to maintain steady blood levels. The long-term safety of propafenone is unknown. Because it is structurally similar to another dangerous anti-arrhythmic medicine, flecainide, caution should be exercised in its use. Flecainide and propafenone, like other antiarrhythmic drugs have been shown to increase the occurrence of dangerous arrhythmias (5.3% for propafenone, Teva phisician prescribing information), primarily in patients with underlying heart disease.

Side effects

Side effects attributed to propafenone include hypersensitivity reactions, lupus-like syndrome, agranulocytopenia, CNS disturbances such as dizziness, lightheadedness, gastrointestinal upset, a metallic taste and bronchospasm. About 20% of patients discontinued the drug due to side effects.

Initiation of therapy

Propafenone generally needs to be started in a hospital setting to assure ECG monitoring of the patient. http://www.mdconsult.com/, micromedex etc. There are many different dosages of propafenone, depending on clinical presentation of the arrhythmia. The treatment is generally begun with relatively high dosages (450-900mg/d) decreasing to near 300 mg/d. In most western countries the accepted maximal dosage is 900mg/d.

For economic and patient convenience reasons, some clinicians are starting certain antiarrhythmic agents in an outpatient setting for some patients. No consensus exists regarding the safety of this practice, and information is needed to determine which agents and which patients are appropriate for outpatient initiation of antiarrhythmic therapy. From a clinical point of view, this drug is used primarily in patients with relatively preserved myocardial function. http://www.ahrq.gov/clinic/epcsums/atrialsum.htm

Contraindications and cautions

Caution should be used in administrating propafenone in individuals with hepatic dysfunction, asthma, CHF, or bradycardia.

Patent issues

The patents for the Rythmol family of products are owned by Reliant Pharmaceuticals, Inc., in Liberty Corner, N.J. Reliant acquired the patents from developer Abbott Laboratories, Inc., in 2003.

Reliant Pharmaceuticals filed a federal patent infringement lawsuit against generic drug maker Par Pharmaceuticals, Inc., on December 19, 2006. The lawsuit, filed in the federal district court for Delaware, seeks to prevent Par from manufacturing a generic version of Rythmol. Par is seeking approval to do so from the U.S. Food and Drug Administration.

Reliant's patent for the drug was issued in October, 1997, and it expires in 2014. Par believes the patent is invalid, according to its filing with the FDA.