Isosorbide Mononitrate

Isosorbide Mononitrate is indicated for the prevention and treatment of angina pectoris due to coronary artery disease. The onset of action of oral isosorbide mononitrate is not sufficiently rapid for this product to be useful in aborting an acute anginal episode.

Isosorbide mononitrate is the major active metabolite of isosorbide dinitrate (ISDN), and most of the clinical activity of the dinitrate is attributable to the mononitrate. The principal pharmacological action of isosorbide mononitrate is relaxation of vascular smooth muscle and consequent dilatation of peripheral arteries and veins, especially the latter. Dilation of the veins promotes peripheral pooling of blood and 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, systolic arterial pressure, and mean arterial pressure (afterload). Dilatation of the coronary arteries also occurs. The relative importance of preload reduction, afterload reduction and coronary dilatation remains undefined.

Tablet: The usual oral dose is 1 tablet (20 mg) 2 times daily, first dose in the morning and another 7 hours apart. Although maintenance doses ranging from 20 mg to 120 mg (1-6 tablets), a dose of 10 mg (1/2 tablet) is suitable when lower dosage is used at the starting of treatment or as directed by a registered physician.

Sustained Release Capsule: The usual oral dose is 1 capsule (50 mg) daily or as directed by the registered physician.

• Concomitant use of Isosorbide Mononitrate with phosphodiesterase inhibitors in any form is contraindicated.
• Concomitant use of Isosorbide Mononitrate with riociguat, a soluble guanylate cyclase stimulator, is contraindicated.
• The vasodilating effects of isosorbide mononitrate may be additive with those of other vasodilators. Alcohol, in particular, has been found to exhibit additive effects of this variety.
• Marked symptomatic orthostatic hypotension has been reported when calcium channel blockers and organic nitrates were used in combination. Dose adjustments of either class of agents may be necessary.

Isosorbide mononitrate is contraindicated in patients who are allergic to it. Do not use Isosorbide Mononitrate in patients who are taking certain drugs for erectile dysfunction (phosphodiesterase inhibitors), such as sildenafil, tadalafil, or vardenafil. Concomitant use can cause severe hypotension, syncope, or myocardial ischemia. Do not use Isosorbide Mononitrate in patients who are taking the soluble guanylate cyclase stimulator riociguat. Concomitant use can cause hypotension.

Headache, feelings of dizziness, hypotension may occur sometimes.

Pregnancy Category B: Reproduction studies performed in rats and rabbits at doses of up to 540 and 810 mg/kg/day, respectively, have revealed no evidence of harm to the fetus due to isosorbide mononitrate. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, Isosorbide Mononitrate should be used during pregnancy only if clearly needed.

Nursing Mothers: It is not known whether isosorbide mononitrate is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when isosorbide mononitrate is administered to a nursing woman.

Severe hypotension, particularly with upright posture, may occur with even small doses of isosorbide mononitrate. This drug should therefore be used with caution in patients who may be volume depleted or who, for whatever reason, are already hypotensive. Hypotension induced by isosorbide mononitrate may be accompanied by paradoxical bradycardia and increased angina pectoris.

Nitrate therapy may aggravate the angina caused by hypertrophic cardiomyopathy. In industrial workers who have had long-term exposure to unknown (presumably high) doses of organic nitrates, tolerance clearly occurs. Chest pain, acute myocardial infarction, and even sudden death have occurred during temporary withdrawal of nitrates from these workers, demonstrating the existence of true physical dependence. The importance of these observations to the routine, clinical use of oral isosorbide mononitrate is not known.

Patients should be told that the antianginal efficacy of Isosorbide Mononitrate tablets can be maintained by carefully following the prescribed schedule of dosing (two doses taken seven hours apart). For most patients, this can be accomplished by taking the first dose on awakening and the second dose 7 hours later.

As with other nitrates, daily headaches sometimes accompany treatment with isosorbide mononitrate. In patients who get these headaches, the headaches are a marker of the activity of the drug. Patients should resist the temptation to avoid headaches by altering the schedule of their treatment with isosorbide mononitrate, since loss of headache may be associated with simultaneous loss of antianginal efficacy. Aspirin and/or acetaminophen, on the other hand, often successfully relieve isosorbide mononitrate-induced headaches with no deleterious effect on isosorbide mononitrate’s antianginal efficacy.

Treatment with isosorbide mononitrate may be associated with light-headedness on standing, especially just after rising from a recumbent or seated position. This effect may be more frequent in patients who have also consumed alcohol.

Symptoms: Most common symptoms are hypotension, throbbing headache, tachycardia, and flushing. Methemoglobinemia may occur with massive doses.

Treatment: Treatment consists of placing patients in recumbent position and administering fluids; alpha-adrenergic vasopressors may be required. Methemoglobinemia should be treated with methyline blue at a dose of 1-2 mg/kg IV slowly.

Nitrates: Coronary vasodilators.

Store at 20°-30°C.