For the management of mild to moderate essential hypertension. It may be used alone or concurrently with thiazide-type diuretics.
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.
Mode 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.
Hepatic. Completely metabolized prior to excretion and no unchanged drug is detected in the urine.
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.
Fletcher H, Roberts G, Mullings A, Forrester T: An open trial comparing isradipine with hydralazine and methyl dopa in the treatment of patients with severe pre-eclampsia. J Obstet Gynaecol. 1999 May;19(3):235-8. Pubmed Ganz M, Mokabberi R, Sica DA: Comparison of blood pressure control with amlodipine and controlled-release isradipine: an open-label, drug substitution study. J Clin Hypertens (Greenwich). 2005 Apr;7(4 Suppl 1):27-31. Pubmed Hattori T, Wang PL: Calcium antagonist isradipine-induced calcium influx through nonselective cation channels in human gingival fibroblasts. Eur J Med Res. 2006 Mar 27;11(3):93-6. Pubmed Johnson BA, Roache JD, Ait-Daoud N, Wallace C, Wells L, Dawes M, Wang Y: Effects of isradipine, a dihydropyridine-class calcium-channel antagonist, on d-methamphetamineês subjective and reinforcing effects. Int J Neuropsychopharmacol. 2005 Jun;8(2):203-13. Pubmed
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