Ivabradine – a novel sinus node inhibitor and anti anginal agent

Ivabradine – a novel sinus node inhibitor and antianginal agent

Ivabradine – a novel sinus node inhibitor and antianginal agent: Ivabradine is available as 5 mg and 7.5 mg tablets. It is a selective and specific inhibitor of the I_f current which is also called the cardiac pacemaker current or “funny” current causing the spontaneous diastolic depolarisation of pacemaker cells. The drug slows down the pacemaker activity of the sinoatrial node and is hence a pure heart rate lowering agent. It has no effect on intra atrial, atrioventricular or intraventricular conduction, nor has it any effect on myocardial contractility.

Ivabradine can also interact with retinal current I_h which closely resemble the cardiac I_f .  This explains the luminous phenomena (phosphenes) experienced by patients on the drug, which is described as transient enhanced brightness in a limited area of the visual field.

At usual recommended doses – starting with 5 mg twice daily, ivabradine reduces the heart rate by about 10 beats per minute at rest and during exercise. This leads to reduced myocardial workload and oxygen consumption. Lower doses of 2.5 mg twice daily may be considered in elderly to avoid bradycardia.
The drug is not recommended in those with atrial fibrillation or other cardiac arrhythmias as the sinus node will not be the dominant pacemaker in such situations and the drug will be ineffective.

Since ivabradine is metabolised by cytochrome P450 3A4 (CYP3A4), it is better avoided along with potent inhibitors of CYP3A4 like azole antifungals and macrolide antibiotics. Moderate inhibitors of CYP3A4 like diltiazem or verapamil will increase the blood levels of ivabradine. Concomitant use of QT prolonging drugs along with ivabradine should also be avoided.