Ivabradine

Ivabradine (INN) (pronounced /ɪˈvæbrədin/) is a novel medication used for the symptomatic management of stable angina pectoris. It is marketed under the trade name Procoralan (Servier), and was also known as S-16257 during its development. Ivabradine acts by reducing the heart rate in a mechanism different from beta blockers and calcium channel blockers, two commonly prescribed antianginal drugs. It is classified as a cardiotonic agent.

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Mode of action

Ivabradine acts on the I_f (f is for "funny", so called because it had unusual properties compared with other current systems known at the time of its discovery) ion current, which is highly expressed in the sinoatrial node. I_f is a mixed Na⁺–K⁺ inward current activated by hyperpolarization and modulated by the autonomic nervous system. It is one of the most important ionic currents for regulating pacemaker activity in the sinoatrial (SA) node. Ivabradine selectively inhibits the pacemaker I_f current in a dose-dependent manner. Blocking this channel reduces cardiac pacemaker activity, slowing the heart rate and allowing more time for blood to flow to the myocardium.^[1][2]

Uses

Ivabradine was approved by the European Medicines Agency in 2005. It is indicated for the symptomatic treatment of stable angina pectoris in patients with normal sinus rhythm, who have a contraindication to or intolerance to beta blockers. It has been shown to be non-inferior to the beta-blocker atenolol for this indication.^[3]. It is also being used off-label in the treatment of inappropriate sinus tachycardia.^[4]

Dosage

A dose of 5 mg twice daily is recommended initially; after 1 month, it is recommended to increase to 7.5 mg twice daily to get the optimal efficacy linked to heart rate reduction. Given limited experience in the elderly, the manufacturer recommends a starting dose of 2.5 mg^[5].

Adverse effects

14.5% of all patients taking ivabradine experience luminous phenomena (by patients described as sensations of enhanced brightness in a fully maintained visual field). This is probably due to blockage of I _h ion channels in the retina which are very similar to cardiac I_f. These symptoms are mild, transient, fully reversible and non-severe. In clinical studies about 1% of all patients had to discontinue the drug because of these sensations, which occurred on average 40 days after commencement of the drug.^[3]

Bradycardia (unusually slow heart rate) occurs at 2% and 5% for doses of 7.5 and 10 mg respectively (compared to 4.3% in atenonol)^[3]. 2.6-4.8% reported headaches^[3]. Other common adverse drug reactions (1–10% of patients) include first-degree AV block, ventricular extrasystoles, dizziness and/or blurred vision.^[6]

Data about long-term safety are in progress but are promising.^{[citation needed]}

Contraindications

Ivabradine is contraindicated in sick sinus syndrome, and cannot be used concominantly with inhibitors of CYP3A4 such as azole antifungals (such as ketoconazole), macrolide antibiotics, nefazodone and the anti-HIV drugs nelfinavir and ritonavir^[5].

References