Isosorbide mononitrate

What is Isosorbide mononitrate?

Isosorbide mononitrate is a prescription medication belonging to the nitrate class of drugs. It is primarily used to prevent chest pain (angina) in people with coronary artery disease and to treat heart failure. This medication works by relaxing and widening blood vessels, which improves blood flow and reduces the heart’s workload.

Uses

• Angina prevention: The primary use is preventing chest pain episodes in patients with stable angina pectoris, particularly for long-term management of coronary artery disease.
• Heart failure treatment: Used in combination with other medications to treat chronic heart failure by reducing the heart’s workload and improving symptoms.
• Esophageal spasm: Sometimes prescribed off-label to treat painful spasms of the esophagus by relaxing smooth muscle tissue.
• Pulmonary hypertension: May be used as part of treatment for certain types of pulmonary hypertension to help reduce pressure in lung blood vessels.
• Post-heart attack care: Occasionally used in the management of patients following myocardial infarction to prevent future cardiac events.

How it works

Isosorbide mononitrate is converted in the body to nitric oxide, a powerful vasodilator that relaxes the smooth muscle in blood vessel walls. This causes both veins and arteries to widen, reducing the amount of blood returning to the heart and decreasing the pressure against which the heart must pump. The result is improved blood flow to the heart muscle and reduced oxygen demand, which helps prevent angina attacks.

Side effects

Common side effects:

• Headache (often severe initially)
• Dizziness or lightheadedness
• Flushing or warmth in face and neck
• Nausea
• Fatigue or weakness
• Low blood pressure
• Rapid heartbeat
• Blurred vision

Serious side effects requiring immediate medical attention:

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• Severe drop in blood pressure with fainting
• Chest pain that worsens or doesn’t improve
• Irregular or very fast heartbeat
• Severe persistent headache
• Signs of methemoglobinemia (bluish skin, difficulty breathing)

Warnings and precautions

• Erectile dysfunction medications: Never take with sildenafil, tadalafil, or other PDE5 inhibitors as this combination can cause life-threatening drops in blood pressure.
• Pregnancy and breastfeeding: Use only when clearly needed during pregnancy; consult healthcare provider about breastfeeding safety as excretion in breast milk is unknown.
• Heart conditions: Use with caution in patients with severe heart valve disease, recent heart attack, or conditions that limit cardiac output.
• Tolerance development: Extended continuous use can lead to tolerance; nitrate-free intervals may be recommended to maintain effectiveness.
• Sudden discontinuation: Do not stop abruptly after long-term use as this may worsen angina; gradual tapering may be necessary.

Interactions

• Phosphodiesterase inhibitors (sildenafil, vardenafil, tadalafil): Dangerous blood pressure drop; combination is contraindicated.
• Blood pressure medications: Enhanced hypotensive effects with ACE inhibitors, beta-blockers, and calcium channel blockers requiring dose monitoring.
• Alcohol: Increases risk of dangerous blood pressure drops and enhanced side effects like dizziness and fainting.
• Tricyclic antidepressants: May increase risk of low blood pressure and require careful monitoring of blood pressure.
• Dihydroergotamine: May reduce the effectiveness of nitrates and potentially worsen angina symptoms.
• Heparin: Nitrates may reduce the anticoagulant effect of heparin, potentially requiring dose adjustments.
• Riociguat: Combination may cause severe hypotension and is generally not recommended.
• Alteplase: Nitrates may reduce the thrombolytic effectiveness of alteplase in heart attack treatment.

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Dosage

The typical adult dosage for angina prevention ranges from 20mg to 40mg twice daily, usually taken in the morning and early afternoon to allow for a nitrate-free period overnight. For heart failure, dosing may start at 10mg twice daily and be gradually increased to 20-40mg twice daily as tolerated. Extended-release formulations may be taken once daily, typically 30-60mg in the morning. The specific dose and schedule should always be determined by a healthcare provider based on individual patient factors, response to treatment, and other medications being taken. Doses should be spaced to provide a nitrate-free interval of 10-14 hours to prevent tolerance development.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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