Monosor (isosorbide mononitrate): Uses, Dosage & Side Effects

What it's for (Indications)

Isosorbide mononitrate is primarily indicated for the prophylaxis and long-term treatment of angina pectoris due to coronary artery disease.
It is not intended for the acute relief of anginal attacks.
Its extended-release formulations are particularly beneficial for maintaining sustained anti-anginal effects and improving exercise tolerance in patients with chronic stable angina.
This medication helps to significantly reduce the frequency, severity, and duration of anginal episodes by improving the balance between myocardial oxygen supply and demand, thereby enhancing the quality of life for individuals suffering from recurrent chest pain.

Dosage Information

Type	Guideline
Standard	The typical starting dosage for isosorbide mononitrate extended-release formulations (e.g., Monis XR) is 30 mg or 60 mg orally once daily, usually in the morning upon awakening, to ensure an eccentric dosing regimen that allows for a necessary nitrate-free interval to minimize tolerance development. The dosage may be carefully titrated based on individual patient response and tolerability, with a maximum recommended dose of 120 mg once daily. It is critical for patients to swallow extended-release tablets whole without crushing, chewing, or dividing them, as this can lead to rapid drug release and potentially dangerous hemodynamic effects. For immediate-release formulations, dosing is typically twice daily with an appropriate interval (e.g., 7 hours apart) followed by a 17-hour nitrate-free period.

Type

Guideline

Standard

The typical starting dosage for isosorbide mononitrate extended-release formulations (e.g., Monis XR) is 30 mg or 60 mg orally once daily, usually in the morning upon awakening, to ensure an eccentric dosing regimen that allows for a necessary nitrate-free interval to minimize tolerance development. The dosage may be carefully titrated based on individual patient response and tolerability, with a maximum recommended dose of 120 mg once daily. It is critical for patients to swallow extended-release tablets whole without crushing, chewing, or dividing them, as this can lead to rapid drug release and potentially dangerous hemodynamic effects. For immediate-release formulations, dosing is typically twice daily with an appropriate interval (e.g., 7 hours apart) followed by a 17-hour nitrate-free period.

Safety & Warnings

Common Side Effects

Common side effects associated with isosorbide mononitrate therapy are predominantly related to its potent vasodilatory properties.
These frequently include headache, which can be severe but often lessens with continued treatment, dizziness, lightheadedness, facial flushing, and hypotension (low blood pressure).
Nausea, vomiting, and dyspepsia are also reported.
Less common but potentially serious adverse events include syncope (fainting), reflex tachycardia (increased heart rate in response to low blood pressure), and severe orthostatic hypotension, particularly upon initiation of therapy or during dose escalation.
Patients should be counseled on these potential effects and advised on strategies to mitigate them, such as rising slowly from a sitting or lying position to prevent dizziness and falls.

Serious Warnings

Black Box Warning: Isosorbide mononitrate does not carry an FDA-mandated Black Box Warning. However, critical safety warnings are paramount for its safe prescribing and patient education to prevent serious adverse outcomes. The most significant safety concern is the profound and potentially life-threatening hypotensive interaction that occurs when isosorbide mononitrate is administered concurrently with phosphodiesterase-5 (PDE5) inhibitors (e.g., sildenafil, tadalafil, vardenafil), as well as with riociguat. This interaction can precipitate severe hypotension, leading to myocardial ischemia, syncope, and potentially fatal cardiovascular events. Patients must be unequivocally warned against taking these medications together. Additionally, caution is strongly advised in patients with circulatory failure, severe hypotension, or conditions that could be exacerbated by vasodilation, such as hypertrophic obstructive cardiomyopathy, where it may worsen outflow obstruction. Close monitoring for orthostatic hypotension, particularly upon treatment initiation or dose adjustments, is essential. This medication is exclusively for the prevention of angina and is ineffective for acute angina relief.
Isosorbide mononitrate should be used with extreme caution in patients with severe hypotension, restrictive cardiomyopathy, constrictive pericarditis, or conditions associated with low cardiac filling pressures, as profound hypotension and reduced cardiac output may occur.
The development of tolerance to nitrates can occur with continuous, uninterrupted exposure; therefore, an eccentric dosing regimen (e.
g.
, once-daily dosing for extended-release preparations) is crucial to provide a nitrate-free interval and maintain therapeutic efficacy.
Concomitant use with phosphodiesterase-5 (PDE5) inhibitors, such as sildenafil, tadalafil, or vardenafil, is strictly contraindicated due to the potential for severe, life-threatening hypotension and cardiovascular collapse.
Patients must be explicitly warned about this critical interaction.
Abrupt withdrawal of isosorbide mononitrate may exacerbate angina, necessitating a gradual tapering of the dose.
It is not indicated for the acute relief of angina.

How it Works (Mechanism of Action)

Isosorbide mononitrate, the active metabolite of isosorbide dinitrate, exerts its therapeutic effects by serving as a source of nitric oxide (NO) within vascular smooth muscle cells. Nitric oxide activates guanylate cyclase, an enzyme that catalyzes the synthesis of cyclic guanosine monophosphate (cGMP) from guanosine triphosphate. Increased intracellular cGMP levels lead to a cascade of events resulting in the dephosphorylation of myosin light chains and subsequent relaxation of vascular smooth muscle. This vasodilation primarily affects venous capacitance vessels, leading to a reduction in venous return to the heart (preload), which significantly decreases myocardial oxygen demand. At higher doses, it also causes arterial and arteriolar dilation, reducing afterload and further decreasing myocardial oxygen consumption. This combined effect improves the balance between myocardial oxygen supply and demand, thereby preventing angina pectoris.