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Pharmacology: Sorbinate-SR tablet is an oral extended-release formulation of isosorbide mononitrate, the major active metabolite of isosorbide dinitrate: most of the clinical activity of the dinitrate is attributable to the mononitrate. The principal pharmacological action of isosorbide mononitrate and all organic nitrates in general is relaxation of vascular smooth muscle, producing dilatation of peripheral arteries and veins especially the latter. Dilatation of the veins promotes peripheral pooling of blood, decreases venous return to the heart, thereby reducing left ventricular end-diastolic pressure and pulmonary capillary wedge pressure (preload). Arteriolar relaxation reduces systemic vascular resistance, and systolic arterial pressure and mean arterial pressure (afterload). Dilatation of the coronary arteries also occurs.
Pharmacokinetics: Isosorbide mononitrate also is readily absorbed from the GI tract. Following oral administration of extended-release isosorbide mononitrate tablets, peak plasma concentrations of isosorbide mononitrate are reached in about 3-4.5 hours onset of action occurs within 20 minutes and lasts for about 8-10 hours. Unlike isosorbide mononitrate does not undergo first pass hepatic metabolism and bioavailability is 77-80%.
Isosorbide mononitrate is widely distributed with a large apparent volume of distribution.
Isosorbide mononitrate is metabolised to inactive metabolites isosorbide mononitrate glucuronide. Only about 2% of isosorbide mononitrate is excreted unchanged in the urine. An elimination half-life about 4-5 hours has been reported.
Sorbinate SR tablet is a sustained release formulation of isosorbide-5-mononitrate. The active substance independently of pH, over a 10 hours. Compared to ordinary tablets the absorption phase of Sorbinate SR tablet is prolonged and the duration of effect is extended. The extend of Sorbinate SR tablet is about 90% compared to immediate release tablets. Absorption is not significantly affected by food intake.
