Ibutilide

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.

Ibutilide, like other class III antiarrhythmic drugs, blocks delayed rectified potassium current.

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.

Absorption

Ibutilide is intravenously administered. It has a high first-pass metabolism, which results in a poor bioavailability 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 clearance 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.

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 abnormal heart rhythms due to its ability to prolong the QT interval, which can lead to the potentially fatal abnormal heart rhythm known as torsades de pointes. Consequently, the drug is contraindicated in patients that are likely to develop abnormal heart rhythms; this includes persons that have had polymorphic ventricular tachycardia in the past, have a long QT interval, sick sinus syndrome, or a recent myocardial infarction, among others.

Patient Information

This medication will be given intravenously for your heart disease. You will have continuously ECG monitoring during the infusion and 4 hours after your infusion. Some of the minor side effects are headache and irregular heartbeat. If you experience chest pain and respiratory difficulties, you should report to your doctors immediately.