Ibutilide
Encyclopedia
Ibutilide is a Class III antiarrhythmic agent that is indicated for acute cardioconversion of atrial fibrillation
and atrial flutter
of a recent onset to sinus rhythm. It exerts its antiarrhythmic effect by induction of slow inward sodium current, which prolongs action potential and refractory period (physiology) of myocardial cells. Because of its Class III antiarrhythmic activity, there should not be concomitant administration of Class Ia and Class III agents.
Ibutilide is marketed as Corvert by Pfizer
. Administration resulted in successful heart rhythm control in 31-44% of patients within 90 minutes, with sustained polymorphic ventricular tachycardia
in 0.9-2.5% of patients. It appears to show better results in atrial flutter as compared to atrial fibrillation.
It does have action on the slow sodium channel and promotes the influx of sodium through these slow channels.
Although potassium current seems to play a role, their interactions are complex and not well understood. Ibutilide’s unique mechanism works by an activation of a specific inward sodium current, thus producing its therapeutic response in which a prolonged action potential
increases myocytes’ cardiac refractoriness in case of atrial fibrillation and flutter.
when taken orally. Individual pharmacokinetic properties are highly viable during the clinical trial.
that closes to the hepatic blood flow (29mL/min/kg). Its metabolic pathway is via liver’s cytochrome P450 system by isoenzymes other than CYP3A4
and CYP2D6
by which the heptyl side chain of ibutilide is oxidized. With eight metabolites are detected in the urine, however, only one is an active metabolite that shares the similar electrophysiologic property of the Class III antiarrhythmic agents. The plasma concentration of this metabolite is only less than 10% of ibutilide.
. Consequently, the drug is contraindicated in patients that are likely to develop arrhythmia; this includes patients that had polymorphic ventricular tachycardia in the past, QT prolongation, sick sinus syndrome
, recent myocardial infarction
, and others.
Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
and atrial flutter
Atrial flutter
Atrial flutter is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia , and falls into the category of supra-ventricular tachycardias. While this rhythm occurs most often in individuals with...
of a recent onset to sinus rhythm. It exerts its antiarrhythmic effect by induction of slow inward sodium current, which prolongs action potential and refractory period (physiology) of myocardial cells. Because of its Class III antiarrhythmic activity, there should not be concomitant administration of Class Ia and Class III agents.
Ibutilide is marketed as Corvert by Pfizer
Pfizer
Pfizer, Inc. is an American multinational pharmaceutical corporation. The company is based in New York City, New York with its research headquarters in Groton, Connecticut, United States...
. Administration resulted in successful heart rhythm control in 31-44% of patients within 90 minutes, with sustained polymorphic ventricular tachycardia
Ventricular tachycardia
Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...
in 0.9-2.5% of patients. It appears to show better results in atrial flutter as compared to atrial fibrillation.
Mechanism of action
Unlike most other Class III antiarrhythmic drugs, ibutilide does not produce its prolongation of action potential via blockade of cardiac delayed rectifier of potassium current, nor does it have a sodium-blocking, antiadrenergic, and calcium blocking activity that other Class III agents possess. Thus it is often referred as a “pure” Class III antiarrhythmic drug.It does have action on the slow sodium channel and promotes the influx of sodium through these slow channels.
Although potassium current seems to play a role, their interactions are complex and not well understood. Ibutilide’s unique mechanism works by an activation of a specific inward sodium current, thus producing its therapeutic response in which a prolonged action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
increases myocytes’ cardiac refractoriness in case of atrial fibrillation and flutter.
Absorption
Ibutilide is intravenously administered. It has a high first-pass metabolism, which results in a poor bioavailabilityBioavailability
In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...
when taken orally. Individual pharmacokinetic properties are highly viable during the clinical trial.
Distribution
Ibutilide has a relatively large volume of distribution among individual subjects, which is about 11L/kg. Approximately 40% of the drug is bound with plasma albumin of healthy volunteers in a trial. This is also approximately close to patients with atrial fibrillation and flutter.Metabolism
Ibutilide has a high systemic plasma clearanceClearance
A clearance can refer to:* in chess, A positional move, where a player moves a piece occupying a certain square away, replacing it with an allied piece that will strengthen the player's position....
that closes to the hepatic blood flow (29mL/min/kg). Its metabolic pathway is via liver’s cytochrome P450 system by isoenzymes other than CYP3A4
CYP3A4
Cytochrome P450 3A4 , a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body. CYP3A4 is involved in the oxidation of the largest range of substrates of all the CYPs. As a result, CYP3A4 is present in...
and CYP2D6
CYP2D6
Cytochrome P450 2D6 , a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body. Also, many substances are bioactivated by CYP2D6 to form their active compounds...
by which the heptyl side chain of ibutilide is oxidized. With eight metabolites are detected in the urine, however, only one is an active metabolite that shares the similar electrophysiologic property of the Class III antiarrhythmic agents. The plasma concentration of this metabolite is only less than 10% of ibutilide.
Excretion
After administration of ibutilide, it is quickly excreted by renal pathway with a half-life of approximately 6 hours. Approximately 82% of a 0.01 mg/kg dose is excreted in the urine during the trial. Among those, around 7% is excreted as unchanged drug. The reminder of the drug is excreted in feces (about 19%).Adverse effects and contraindications
Like other antiarrhythmics, ibutilide can lead to arrhythmia, especially torsades de pointesTorsades de pointes
Torsades de pointes, or simply torsades, is a French term that literally means "twisting of the points". It was first described by Dessertenne in 1966 and refers to a specific, rare variety of ventricular tachycardia that exhibits distinct characteristics on the electrocardiogram .- Presentation...
. Consequently, the drug is contraindicated in patients that are likely to develop arrhythmia; this includes patients that had polymorphic ventricular tachycardia in the past, QT prolongation, sick sinus syndrome
Sick sinus syndrome
Sick sinus syndrome, also called sinus node dysfunction, is a group of abnormal heart rhythms presumably caused by a malfunction of the sinus node, the heart's primary pacemaker...
, recent myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
, and others.