indication

For the management of mild to moderate essential hypertension. It may be used alone or concurrently with thiazide-type diuretics.

pharmacology

Isradipine decreases arterial smooth muscle contractility and subsequent vasoconstriction by inhibiting the influx of calcium ions through L-type calcium channels. Calcium ions entering the cell through these channels bind to calmodulin. Calcium-bound calmodulin then binds to and activates myosin light chain kinase (MLCK). Activated MLCK catalyzes the phosphorylation of the regulatory light chain subunit of myosin, a key step in muscle contraction. Signal amplification is achieved by calcium-induced calcium release from the sarcoplasmic reticulum through ryanodine receptors. Inhibition of the initial influx of calcium decreases the contractile activity of arterial smooth muscle cells and results in vasodilation. The vasodilatory effects of isradipine result in an overall decrease in blood pressure.

mechanism of action

Isradipine belongs to the dihydropyridine (DHP) class of calcium channel blockers (CCBs), the most widely used class of CCBs. There are at least five different types of calcium channels in Homo sapiens: L-, N-, P/Q-, R- and T-type. CCBs target L-type calcium channels, the major channel in muscle cells that mediates contraction. Similar to other DHP CCBs, isradipine binds directly to inactive calcium channels stabilizing their inactive conformation. Since arterial smooth muscle depolarizations are longer in duration than cardiac muscle depolarizations, inactive channels are more prevalent in smooth muscle cells. Alternative splicing of the alpha-1 subunit of the channel gives isradipine additional arterial selectivity. At therapeutic sub-toxic concentrations, isradipine has little effect on cardiac myocytes and conduction cells.

toxicity

Symptoms of overdose include lethargy, sinus tachycardia, and transient hypotension. Significant lethality was observed in mice given oral doses of over 200 mg/kg and rabbits given about 50 mg/kg of isradipine. Rats tolerated doses of over 2000 mg/kg without effects on survival.

biotransformation

Hepatic. Completely metabolized prior to excretion and no unchanged drug is detected in the urine.

absorption

Isradipine is 90%-95% absorbed and is subject to extensive first-pass metabolism, resulting in a bioavailability of about 15%-24%.

half life

8 hours

route of elimination

Approximately 60% to 65% of an administered dose is excreted in the urine and 25% to 30% in the feces.

drug interactions

Artemether: Additive QTc-prolongation may occur. Concomitant therapy should be avoided.

Lumefantrine: Additive QTc-prolongation may occur. Concomitant therapy should be avoided.

Quinupristin: This combination presents an increased risk of toxicity

Tacrolimus: Additive QTc-prolongation may occur increasing the risk of serious ventricular arrhythmias. Concomitant therapy should be used with caution.

Telithromycin: Telithromycin may reduce clearance of Isradipine. Consider alternate therapy or monitor for changes in the therapeutic/adverse effects of Isradipine if Telithromycin is initiated, discontinued or dose changed.

Thiopental: The CYP3A4 inducer, Thiopental, may increase the metabolism and clearance of Isradipine, a CYP3A4 substrate. Monitor for changes in the therapeutic/adverse effects of Isradipine if Thiopental is initiated, discontinued or dose changed.

Thiothixene: May cause additive QTc-prolonging effects. Increased risk of ventricular arrhythmias. Consider alternate therapy. Thorough risk:benefit assessment is required prior to co-administration.

Tipranavir: Tipranavir may decrease the metabolism and clearance of the calcium channel blocker, Isradipine. Monitor for changes in Isradipine therapeutic and adverse effects if Tipranavir is initiated, discontinued or dose changed.

Toremifene: Additive QTc-prolongation may occur, increasing the risk of serious ventricular arrhythmias. Consider alternate therapy. A thorough risk:benefit assessment is required prior to co-administration.

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.

Trimipramine: Additive QTc-prolongation may occur, increasing the risk of serious ventricular arrhythmias. Concomitant therapy should be used with caution.

Voriconazole: Voriconazole, a strong CYP3A4 inhibitor, may increase the serum concentration of isradipine by decreasing its metabolism. Additive QTc prolongation may also occur. Consider alternate therapy or monitor for changes in the therapeutic and adverse effects of isradipine if voriconazole is initiated, discontinued or dose changed.

Vorinostat: Additive QTc prolongation may occur. Consider alternate therapy or monitor for QTc prolongation as this can lead to Torsade de Pointes (TdP).

Ziprasidone: Additive QTc-prolonging effects may increase the risk of severe arrhythmias. Concomitant therapy is contraindicated.

Zuclopenthixol: Additive QTc prolongation may occur. Consider alternate therapy or use caution and monitor for QTc prolongation as this can lead to Torsade de Pointes (TdP).